CA1116277A - Method and means for determining positions of reflectors with fan-shaped beams - Google Patents

Abstract

Abstract of the Disclosure The positions of target reflectors at a distance from a measuring station are measured with fan-shaped annularly sweeping beams of radiation emitted from the measuring station and reflected back to a detector there when each beam is intercepted by a reflector. Expected reflector distribution is analyzed to ascertain, as between adjacent reflectors at equal distances from the station, the minimum projected distance expectable between such reflectors in a separation direction in which separation can be maximum and the maximun projected distance between then in the transverse direction. Each of at left two beams has its long cross-section dimension oriented to be at an angle to that of the other and at an angle to the separation direction which is such that its tangent value is greater than the ratio of said maximum distance to said minimum distance. Each of those beams is swept to move between intersection with an origin point on one side of a solid angle space swept by the beam and intersection with another point that is on the opposite side of said space and is spaced in the separation direction from the origin point. Angular positions of both beams are aligned increasing magnitudes with increasing distance from the origin point, for unambiguous measurement of target posi-tions. For a given orientation of long cross-section dimensions of each beam, targets at like distances from the station must each be in an hour-glass-shaped region of isolation related to that beam orientation.

Description

7~
.-- 1 --~ETHOD AND MEANS FOR
DETERMINING POSITIONC OF RE~LECTORS
~ITH FAN-SHAPED B~IS

~ Field of the Invention `~ This invention relates to a method and means for ascertaining the position of a ~ody that is at a distance from a measuring location; and the invention is more . 5 pa~tict~l æ ly onc~rned with measurement of the loca~ion .~ of each o~ a pluxality of such bodies with the us~ o~ .

~an-shap~d beam3 of radiation that ar~ swept ~la~7~se .

" angularly.

:
Syst~ms for de~ermining ~he position o~ a radiation-reflec~i~g body ha~e been proposed wherein two fa~-shaped ~` beams of radiatio~, such a~ laser ~adiation, were swept flàtwise angularly across a solid angle ~hat had ~he emitter of the rad-iation at its apex~ By reason of the anwise di~ergence of each beam in ~he direction a~Jay from . ~he e ~ tter~ each beam had a long dimension in cross-section and-a transverse narrow or.e. In most such prior systems.
~ach ~eam had.its said long dimension oriented at right -~
angles ~o that of ~he other and was swept ~ransversely to 20 tha~ l~n~ d~men~ionO U~ually the beams were sw~pt alt~r- ~
. ~nat~ly in a repetitive sweep cycle. By taking note of the ~;
angular position of ~ach beam in its sweep at ~he instant .:
when a reflection from a body was received at ~he emitter location, two o th~ ~hree o~ordinates tha~ de~ine the 25 position o~ the body in the space ~wept by the be~ms could ~;
be Xnown.
' ~
.. . .

-. , ~ .: ; , - , . .
.. .. .. ., ., ,. ., . : "
..

,;, ,:
. . . ~ . . , . . ,..; . ,, . ;,. , 7'7

- 2 -:; .
It is also readily possible to obtain information . about the distance between a radiation emitter and 2 reflecting body by measuring the ti~e interval bet~teen emissi~n o~ radiation and reception of the reflected 5 radiation at the emltterO ~hat time interval is of - - cou~s~ a simpl~ ~unction of ~he distance to b~ measured, eretofore ~hes~ ~heoretical possi~ilities ~or de~er- .-~ . ~in~n~ th~ locatio~ o~ a reflecting body ~y means o~ a pair ~`
.. ` . ~f ~an-~hap~d, ~latwis~ swe~p~g beam~ o~ radiatio~ could ~`
.. . . .; . . .
.~ .; - 10 be sa~isfa~b~r~ly realized only on the conai~ion ~ha~

~ t~er~ wa~ n.Q moxe tha~ one such body i~ ~he space swep~ ~y .. :
. . .
;- .: .:- th~ beams. A~ soon as two or more snch boaies were-pre~en~

. in t~at 3pace, they gav~ rise to a probl~m of .ambiguitY .~ . -:, . . . .
.~ . to which the~:e wa~ no comple~el~r satisfacto~ solution.
15 ~ . The.natu~ of the :am~iguitv problem is pointed out i~ U.~;. Pate~ts Nos. 2,514,617 and 3,056,129, both issuea to W. J. Albersheim. The problem can be more fully . `
~naerstood fr.om a considera~ion c:E Fig. 1 o~ the accom-,. . ;. . .. :
~n~ng drawi~gs,.wherein.fan-shaped be~ms x and y are shown ... . ................ . . . -` 20 in crs:~ss-~ec~ion. Those two bea~s alterna~ely sweep acxos~ - ~
a~spàc:e ~', the be~ x being swept 1atwise ho~zon1:ally an~ :
the ~eam y being~ swept :Elatwise ver1:icall~. If xelec:ting .
.. . . . , ~ . . .
bodie3 are pres~t ~n ~he 5pa~e at the positions ~enoted .by A an~ B, ~hen a ~eflection will be dete~ed at t~e~

beam em~tte~ locatlon at the i~stant whe~ the x ~eam is a~ - .
. ' ' ~L ., the posi~ion o its swe~p designated by x and again when .it is at the.posi~ion ~esignaged b~ x . 5Iml1ar1~, re~lec-. . . . . . . . . , - ~
tions of the y b~am will be recei~ed at ~he instan~ when .

` ?

- - . . . , . . ~
- , ': ' :

"
. :;

~ ` ~
7t7

- 3 -it is in its angular ~ositions of sweep that are respectivelydesignated by yl and ~ y . These received reflections correspond to four possible positions A, B, C, D at which reflecting bodies may be present in the s~ept space, and f~om the available in~ormation it is equally as probable ~hat bodie~ are present at positions ~ and D as at positions A and B~
In ~eneral, such an ~m~lguity ca~ arise whene~er ~he numbe~ of re1ecto~s in a space swept by fan-shaped beams is equal to or gre~ter ~an ~he num~er of beams sweeping ~he paca. The ~mplication of this principle is that ambiguities coul~ be resolved by the employment of a sufficiently large n~mber o discrete beams. But it is ob~ious that if the pre--sence of numerous reflecting bodie$ could be expected, it would e difficult to generate a suficient num~er o~ beams, all oriented at different angles~ ahd~to synchronize their sevèral sweeps ana ~alculate the measurement results obtained ~ith them.
~e two Albers~eim patents suggast the employment o .
so-called range gat~ng ~y which indications are ~ccepted onl~ ~rom those targets that are at a predetermlned dis~ancs ~:
from t~e measuring station, or within a predetermined~ ~ -range o distance~ from that station. Range gating can reduce the number of bodies that ~ust be identified, ~ut it is o no avail whe~ two reflecting bodies are at the same distance f~om the measuring station and gi~e rise to the ambiguity problem just explained. Albersheim Patent No. 2,514,617 pr~posed an expedient for xesolving ~at -- ,.

`: '' : . , ': - ', ., .. . .

. . : ' l '.'.,, ' :, ' : .
:, . , ~' `: ' . ' ' ': ' ' . ' :.' , , ; , .
.,',. ' , ' !
~ ~ . . ' ' ' ',, ~

' . - a -.` am~iguity, but as s~ated in the later Albersheim patent, the system o~ tha~ earlier Datent required the performance of a nu~er of ti~e co~su~ing operational ste~s and was ; therefore unsatisfactory in applications where time was o~
S ~he essence. The later Albersheim patent proposed an ~` ex~edient which reguixed more complicated and costly appara-tus ana ~-hich, although faster, was still rather slcw ~n th it required th3 per~ormance o~ several calculating operations for the pu~po~ Of o~taining inormatio~ abou~ actualre~lec~or 1~ locàtion9. T~e~è is al~o r@ason to doubt ~hat ~he system of the later Albersh~l~ patent could produce un ~ iguous resul~5 , under all circumstance~. -~ hose slcilled in this field o:E art will recognize that `~h~re are`a ~arioty of applications in which fan-shaped flatwis~ sweeping beams could be used for complete measurement .o~ re1ecting.body. : loca~ions, given a ~olution to ~he..
problem of unambiguous ide~ti~ication o~ individual bodies w~en plural ~odies~ appear in the space swept by the ~eams and particularly ~7hen two or more bodies in that space are at the same distance from the ~easuring station, As examples of such applications, mention can be made o~ sys~
tems for sup~rvision and control o~ taxiing ai~cra~t on an -airport, measurement of air or water cur~ents by tracking of balloons or floats that move with the cur~2n~, a~d con~
tinuous measure~ent of positions of boats in a sailing - `
competition.
~n application which is of particular concer~, and .. . ........ . . . . .
which particularl~ exemQliie5 the utility o~ ~he prese~t : . .

:

-, ' ~ . .

; - 5 ~
~;
invention, is that of measurement of target location in - simulated weapons fire scoring systems. One such system is disclosed in U.S. Patent No. 3,832,791, wherein a beam . , having a substantial amount of divergence was emitted from -i 5 the weapon location so that any target at which the weapon - was aimed could reflect radiation back to the weapon location, notwithstanding gun elevation and aiming lead to - compensate for target movement. A first emission o~ the beiam~ occuring at the instant of simuLatea firing, was employed to obtain a ranging fix on the targPt: and after an interval equal to the calculated time re~uired or a round of ammunition to arrive at the target, a second emission of the beam was-modulated to encode information . .
about ammunition type ~;point of impact of the simulatea round in relation to the target, so that hit effect could - be evaluated at the target O Because of the divergence of ` the beam, it was necessary to have a specialized and relatively ex~ensive detector that could distinguish be-tween reflections from target reflectors that were at the same range and relatively close to one another, and trans-missions could not be made on the beam exclusively to a - detector co-located with a particular one of such reflectors.
Therefore there were many tactical situations in which`
`. accurate scoring results could not be obtained. As a 25 further result of the divergence of the beam and the con- ;
sequent diffusion of its radiation, the system had rela-.
tively poor range for a given i~mount of radiation energy ` and had a poor ratio of signal to background aisturbance.

. . ~

~ ' .. . .., .. ~,i, , By contrask, the general ob~ect of the pre~ent inven-tion is to provide a measuring system wherein beamed radi--.~. ation is employed for accurate determination of the position -. of a reflecting target, which system is be-tter suited to `- 5 simulated weapons fire scoring applications than prior :- such systems, and is also very advantageously applicable to many other types of equipment for r~mote measurement of positions of objects.
Application of the present invention to a system for ; 10 scoring simulated gunnery practice requires the solution of certain further problems, and with respect to these the present dis~ osu ~ is supplemented by the disclosures of two copending~applications, Serial No~ ~7~ 9 y and Serial No. ~
Serial No. 3~7, 5~ ~ relates to a method and means for effecting selective delivery of information encoded in the modulations of flatwise sweeping fan-shaped beams, so that information intended only for one of a plurality of bodies in the space swept by the beams will be delivered exclusively to that one body.
~he other copending application, Serial No. 3~7~7~59 ~ ~
is somewhat more closely related to the subject matter of `~
.~ . the present invention, inasmuch as it disclose~ a gunnery practice scoring system which, in one of its operating ` 25 modes, employs periodically sweeping fan-shaped beams for making measurements of target position from and after the instant of simulated firing of a weapon, and simul-taneously makes a calculation of the position of an imagin-ary projectile in its trajectory. The trajectory calcul-ation simulates the flight that a selected type of real :

3~7-- 7 projectile would have had if fired from the weapon with its - barrel axis oriented as at the instant of simulated firing.
At the instant when the calculated ~osition of the imaginary projectile brings it to a distance from the weapon location :~ 5 that is equal to the weapon-to-target distance, or when the -Lmaginary projectile reaches a predetermined elevation relative to target elevation, the calculation can stop and results can be scored at the weapon location on the basis of the relationship between projectile position and target position at that instant.
In such a scoring system, each target comprises a reflector by which intercepted radiation emitted from the weapon location is`reflected back to that location.
The beams are pulsed so that reflected radiation, detected 15 at the weapon location, can be employed there for measur- ~`
ing distance to the reflector. Target reflector azimuth - and elevation relative to the weapon location are measured by taking account of the momentary angular position of each beam in its sweep at the .
. . - ~ , . .
.

':

- ' ~ " , ' ' ' ! . ! ~ ;' :, . ~

;. ~ ', ' " ': " . `

', : `'' ' ' '~ `. . .1 '' ,, ` ~' '7~7 time its radiation, reflected from the reflector, is detected at the weapon location.
It will be apparent that accurate and realistic utilization of such a scoring system requires that when reflections are received during the course o~ a beam sweep `` f~m two or m~re target re~lectors that are at equal dis-tances from the weapon position, the scoring apparatus shall not respond to spuIious target positions created by the above described ambigui~y probl~m and should be capabl~ o~ dis-crIminat~g ~etwe~n adjacent reflectors. This reguixement i6 impo~ed ~ecau~e there are many tactical situations -- for . .
example,` t~nX maneuvers -- in which two or more target re- -~lectors may be pres nt in proximity to one ano~her and at , su~stantially ~qual distances from a weapon that has them . 15 in its field o fire, and such ~actical.si~uations should ~e reproduced during training exercises in the interests of training effectiveness. Obviously range gating would~ :
not be satis~actory for unambiguous determination Qf the `-positions o~ithe targets in isuch a si-tuation.
With the ~oregoing considerations in mind, the general`ob~ect o~ the ~resent in~ention can be more fully . -- ~ated as bein~ to provide a method and means fo~ unambig uously a~certainlng at a measuring station, by means of fan-shaped, flatwise sweeping beamg emitted therefr~m, the position relati~e to said station of eac~ of a plurality of reflectors that may be present in a solid angle which is - . !

:`.' .' ., ' ~' :: , "` :'~ '` ' ' ; ., ' ,' ' . , " '' ' '':

`, , , `:` . ` ' . . , .' ` : ' ~,' ` ` , . : `' ' ' ' ',' ., , ` ' ' ` :' '' ' , '' '' ' .' ' ' ` ~ , , , , , , ',; ~ '. ~.. ' , . ' .:' : " : ' : : : :

g swept by the beams and which has the station at its apex.
A more specific object of the invention is to provide a measuring system wherein fan-shaped beæ~s of radiation are emitted from a measuring station and are swept flatwise angularly across a solid angle space that has the measuring - station at its apex, wherein said beams are employed to .
ascertain the position within said space of 2 re~lector of beam radiatio~ that is at a distance from the measuring station, and whereby an unambiguous determination can be . 10 made of the position of each of a plurality of such reflectors that may be present in said space.
, Bnother specific object o th.is i~ventio~, and a very -- ` important one, is to provide a me~hod and means ~or rapidly and e~icien~ly resolving the ambiguity ~hat has here-15 .to~ore arisen with the use of flat~Jise-sweeping fan-shaped beams used for measurement of the positions of reflectors .
in ~he`s~ace swep~ by the beams when the number of reflec- ~`
. ~ tors in that space was equal to or greater than the number f beams employed.
. ` 20 Other objects of the invention include ~he provision of a fas~ methad`of measurement wherein radiation em~t~ed frcm a measuring station is employed to o~tain an unam-biguous measuremen~ of ~he position of each of a group of reflectors in a~ ar~a remote xom the measuring station, `` 25 or of the position of a selected one of such re~lectors, and whereby such position measurements can be obta~ned as functions of range, azimuth and eleva~ion relatiYe to ~he measuring station, which method can be pra~ticed with .
simple aut~matic equipment, ensures good range and high`
.

~ ` -- 10 --sensitivity by reason of lo~ radiation diffusion, and affords the eapability for discri~inating between re~lec~ors tha. are relatively cl.ose to one another.
Su~mary of the Inyention The objects o~ the invention ar~ achie~ed in apparatus .
by which the position of any one of a plurality of re~le~-- tors can be unambiguously determined in relation to a meas~rin~ station at the apex`of a solid angle spa~e in which the reflectors are located, each o~ said reflectoxs being of the type whereb~ intercepted radiation is re~lected in the direction dir~ctly opposite to the one from w~ich .-it arrived at the re~lector~ and the refleckors being so distributed in said space that adjacent reflectors at equal distances frcm ~aid station will always be sepàrated by at least a minlmum projected distance in a separation dixec-tion and will be separated by no more ~han a maximu~ pro- :
jQcted distance in a direction transverse to said separation direction, said apparatus being of the type ~omprising a .
radiation emitter at the measuring station for emitting a ~0 pl~rality of fan-shape~ beams o~ radiation, each of whi~h has a long cross-section dLmension and a short cross-se~tion ~ :
d~mension,.said emitter being arranyed to ~weep each beam angularly, substantially transversely to its said long .
dimension, acros~ said solid angle space, said apparatus - .. ~`;
being characteri~ed by: sald emitter bein~ further arranged to emit at least two o~ said beam~ wi~h their said lqng .
. ~ , . .
dimen~ions oriented at an angle to one another`and at an ~ .
i'` ' ' ". ' ' '' .~.'' ' "~ ' ' ~: . ' !

~, , . :
.`

y~

angle to said separation direction which is such as to have a tangent value at least equal to the ratio of said maximum distance to said minimum distance, and to sweep each of said at least two beams in a direction such that each is carried between its intersection with an origin - point at one side of said space and its intersection with another point which is at the opposite side of said space ; and which is spaced in said separation direction from the origin point. For each of said at least two be~ms, increasing magnitudes are consistently assigned to angular positions at increasing distances from the origin side~
Whenever a re~lection of one of said two beams is detected at the measuring station, the magnitude of the angular ~`~ position of that beam at that instant is stored, and 15 reflector positions are unambiguously ascertained ~y coupling `
stored values for each of said two ~eams, in a consistently progressive order of magnitude, with those for the other, taken in the same orderO
Brief Description of Drawings In the accompanying drawings, which illustrate embodî-ments of the invention now regarded as the pre~erred modes of practicing its principles:
Fig. l is a view in cross-section of a space swept by a pair of fan-shaped beams, illustrating the problem~of measurement ambiguity that is solved by the present invention;
Fig. 2 is a perspective view of a simulated tactical situation illustrating the application of the principles of the present invention to the scoring of simulated weapon fire;
"` ' ` ':

Fig. 3 is a perspective view illustrating a reflector mounted on a target body, shown in relation to a region around that reflector in which no other reflector is to be present in accordance with the principles of this invention;
Fig. 4 is a block diagram of apparatus embodying the principles of this invention;
Fig. i is a view generally similar to Fig,. 1 but illustrating a beam arrangement that embodies the prin-ciples of this invention and is suitable for cooperationwith the re~lector arrangement shown in Fig. 3;
Fig. 6 is a view of a pair of radiation beams, taken transversely to their direction of propagation, that are in another arrangement which is in accordance with the 15 principles of this invention; '"' Fig. 7 is a view in cross-section of the space swept by the beams shown in Fig. 6;
Fig. 8 is a diagrammatic view explaining how, wi~h tha application of the principles of this invention, unam-`2~ biguous measurements can be made on target reflectors thatare closely adjacent to one another;
~igO 9 is a view generally similar to Fig. 6 but ~' illustrating another beam arrangement that is in accordance with the principles of this invention;
~` 25 Fig. 10 is a diagrammatic view illustrating certain relationships of beam positions to targets and explaining ~` how target positions are unambiguously ascertained; ~, , Fig. 11 illustrates still another beam arrangement that is in accordancc with the principles of this invention;

~`~
`

7 ~

Fig. 12 is a diagrammatic view showing how criterion beams are oriented in relation to expectable reflector distributions;
Fig. 13 is a diagr~m illustrating direction of sweep of criterion beams; and Fig. 14 is a diagram of various permissible arrange-- ments in relation to one another of reflector pairs at like distances from the measuring station.
~etailed Description of the Invention "` 10 Referring now to the accompanying drawings, Fig~ 1 ` illustrates a training exercise involving use of a weapon `~`~
5 carried by a tank 2 for simulated firing at one of a ` group of real or dummy target bodies 10, 10', 10".
Aiming and simulated firing of the weapon 2 are in - .
all respec~s carried out as for firing of a real projec-tile, but for training purposes the weapon 5 is equipped with measuring apparatus that ~omprises (see Fig. 4) a radiation emitter 3 which preferably comprises a laser, a radiation detector 4, and a control device 6 that coordinates operation of the radiation emitter 3 and detector 4 with the firing mechanism of the weapon S.
Each of the target bodies 10, 10', 10" is e~uipped with at least one reflector 13, in each case a so-called corner ~eflector or retroreflector by which radiation that falls ` 25 upon the reflector is reflected in the direction directly opposite to the one from which it arrived. (For clarity - Fig. 4 shows the path of reflected radiation as somewhat divergent from that of emitted radiation.) Thus, upon simulated firing of the weapon 5, the emitter 3 is caused i';
to emit radiation towards the target bodies 10, 10', 10", `` '' ..

and such radiation, reflected back to the weapon location 2 and detected by the detector 4, is employed for measuring target positio~ in range, azimuth and elevation in relation to the weapon location. Since measurements are always made - 5 to a reflector, rather than to a target body gene~ally, the terms target and reflector are herein used synonymously.
For explanation of how measurements made with radia-tion rom the emitter 3 are employed in scoring the results obtained with simulated firing, reference-may be made to the above-mentioned copending application, Serial No. ~5~ owever, without further details it will be apparent that for vaild and accurate scoring results such measurements must be made unambiguously, and must not be made on spurious reflector positions such as would arise with prior systems as a result of the presence of a plurality of reflectors in the target area.
It will be understood that weapon fire scoring apparatus is merely illustrative of the many possible ~` applications for the present invention, and that the weapon location exemplified by the tank 2 typifies any . ~ measuring station from which the position of each of a -~
,~ plurality of remote reflecting objects or bodies can be unambiguously ascertained with the use of radiation in ~`~ accordance with the principles of his invention.

:':

'` , ' '' .~
!

' ~ ` ` . ~ ` ' ; ' ' ' " .. ' ' ' '; .: " ' ,., ~ ` ' ' . :' ':" ~ ' ' ., ' ' ' ' ` :

`. . , ` , :: ,, ` ~ . . , ~

In accordance with the invention, -the radiation emitted from the laser 3 is formed into fan-shaped beams 7' and 7" in a ~nown manner. As shown in Fiy. 1 there - are only two beams, but it will be understood that the radiation could be formed into three or more beams.
- In cross section ~ e., transversely to the direction o~ propagation, as the beams are shown at 8', 8" -- each ~`
beam has a long dimension and a relatively short dimension that is transverse to its long dimension. Thus each beam diverges in the direction of propagation in its long cross-section dimension but has very little such divergence in the transverse cross-section dimension.
Each of the beams into which the radiation is formed should have its long cross-section dimension at an angle to that of every other beam. Although not essential, it is usually advantageous if the beams have a symmetrical relationship of their long cross-section dimensions to one .- another, as for example two beams can have their long `` cross-section dimensions at equal but opposite oblique 20 angles to the vertical, and if there is a third beam it `
can be oriented either vertically or horizontally, -depending upon sweep direction.

1, :

By means of a deflection device 11 that is associated . with the emitter 3 and the detector 4, each beam is swept . angularly, substantially transversely to its long dimension, so that the beams collectively sweep a solid angle space that has the measuring station 2 at its apex. The object or objects to which measurements will be made by means of the beams will of course be located in that solid angle space, in this case in a target area 9.
The de~lecting device 11 by which sweeping motion of the beams is produced can comprise optical wedges that move relative to one another and are located in an optical path that is common to the emitter 3 and the detector 4. The deflection device 11, the laser 3 and the detector 4 can . be built as a unified assembly that is detachably mounted . 15 on or in the barrel of the weapon 5.
- The beams may be swept either sequentially or simul-. ~ taneously, and each beam may sweep either back and forth . or always in one direction, but in any case it will be ~`. - preferable for the beams to have a consistent pattern of . - 20 sweep and to make their respective sweeps in the course . of a repetitive sweep cycle having a predetermined ~uration.
' ' ' -' . ':
. ................................................ ' .

`'~, ~.
.~ . ~, ~ .
. ;~
.~

"~ " , .;`~ ' ..

:., . . , , :
.
. ..

2'~f~7 For the purpose of distance measurement, the beam radiation is pulsed. Such pulsing can take the form of a modulation by which information is encoded in the beam for transmission to all bodies that intercept the beam or : 5 for transmission to a particular one of such bodies, as ' explained in the copending application, Serial No.36~J~9 ~.
When a pulse of radiation is emitted, a signal is sent from the emitter 3 to a calculating device 12, and sub-seguently, when a reflection of the emitted radiation is detected by the detector 4, the detector converts it into an electrical impulse which is also sent to the calculating device 12. Distance from the measuring station to the target is thus measured on the-basis of time elapsed between emission of radiation and receipt of its reflection. The output of the calculating device 12 is fed to a suitable display device 14. The contro- device 6 that is connected . , .
, ' ~',~

:
` j '~

~ ~ .

- 18 - .
with the firing mechanism of the weapon times the emission of radiation pulses from the laser 3 and the cycling of the . deflection device 11 and controls the feediny of signals to the calculating device 12.
As the deflection device 11 causes the beams to swing in their sweeps, it issues signals which, at every instant, correspond to the momentary angular position of each beam in its sweep. Thus, when a reflection from a target is detected by the detector 4, the control device 6 cause.s 10 the then-prevailing signal from the deflection device 11 .- to be fed to the calculating device 12. Acccordingly, if reflections of each beam in .its sweep are received from a .: reflector during the course of a complete sweep cycle, the ii . .
,~ calculating device 12 receives information from which it , 15 can calcùlate functions of the azimuth and elevation of the " ~ .
target as well as its range, thus completely defining the .

` position of the target in relation to the measuring . : station.

According to the present invention, the heretofore existing problem of ambiguity in the ~easurement of target positions in azimuth and elevation is avoided by a propex .~. . :
~`~ ` ralationship between the orientations of the . `:`
. . .
long dimensions of the two beams (or of at ~` least two of the beams if there are more than two), ~.

:

; . ~`,.
"~ ~ .

~ ~ .
~;, .. ' "

` '~, ;~' , : . ' . , - 18a -and by assinging a proper direction of sweep movement to each of those two beams, all in relation to the expectable distribution of targets or reflectors in the solid angle space swept by the beams. Of particular concern is the relationship between any two adjacent reflect~rs that are at substantially the same distance from the measuring station 2. Reflectors at measurably different distances from the measuring station present no significant problem because it is possible to dis-.
~inguish them from one another at the measuring stationby range gating or by range measurements.
The first step in establishing the beam arrangement, therefore, is to determine the direction in which there is most likely to be a maximum projected distance between adjacent re~lectors that are at the same distance ~rom the measuring station, and that direction of possible maximum separation is herein referred to as the separation direc-` tion. Assuming that the tanks 10, 10' and 10" in Fig. 3 are a' the same distance from the measuring station 2, there can be a maximum separation between them in a hori-zontal or substantial~y harizontal direction beaause they are on the surface of the earth. In this case, therefore, the separation direction can be taken as horizontal.
' Aircraft following a taxiway that leads to an elevated : 25 con~rol~tower comprising a measuring station would tend to `"` have maximum separation in a separation direction that could be regarded as vextical.
`' ` ' . .

.

!
.. ~.,' ~.

. ` ', ~ .

.,`', . , ' ' ~ .. . ' ' . .' . . " . ';' ' : , "

Y7t ~ 18b -In each case the projected distance between reflec-~ors in the direction transverse to the separation direction will vary between zero and sor.le more or less easily ascertainable maximum value. Thus vertical separation between the reflectors 13 and 13' on the respec-tive tanks lO and lO' in Fig. 2 is substantially zero, - and maximum vertical separation would be attained between reflectors 13 and 13" if the tank lO" carrying refle~tor 13" were on the crest of the hill on which it is shown.
~0With the separation direction established, it will - ` ~sually be found that as between adjacent reflectors at the same distance from the measuring station there is an ascertainable minimum projected distanse in that directionO
In the case of the tanks 10, 10', 10" in Fig. ~, each of lS which has its reflector mounted midway between its front and rear ends, the least possible projected distance between reflectors in the horizontal separation directiQn ~s of course substantially equal to the length of a tankO
assumin~ ~hat the tanks will always present their side ~` 20 proiles to the measurin~ station 2 when measurements are to be made. If they may be oriented in any direction, and a reflector is mounted midway between the sides of each ~ tank, the.width of a tank would ~e taken as the minimum `"`' spacing in the measurement direction, since reflectors would be nearest one another with the tanks side by-side.
~'` . ` ' ' . ' ' ' .

".
` ,.
- ~ .
: .
. . : . , ~ . ~ ' ".' ' ' 7~7 ~.8c -Still having regard only to reflectors at the same distance from the measuring station, the orientations of at least two of the beams are established on the basis of the minimum probable projected distance between adja-cent reflectors in the separation direction and the : - maximum probable projected distance between such re~lectors in the transverse direction~ ~ig. 12 depicts these : relationships for two cases that can exist under the s~me .-arbitrarily chosen set of conditions but at different t-i~es. Reflectors E and E' are assumed to be adjacent to on~ another and at the same distance from a measuring station (not shown)~ and they are illustrating as being as cIose to one another as they can get in the separation - .-direction S ~which is here illustratPd as hori~ontal~ and .
as ~ax apart às they can get in the transverse direction ~i.e., vertically3. Hence, the minimum projected dis-tance between them in the separation direction S is given by L and the maximum projected distance be~ween them in ~he ~ransverse direction is given by M. Alternatively~
20- under these same conditions, two adjacent reflectors coula occupy the positions designated by F and F',.but `.` in the natu~e o~ the situation the reflectors Fl F' cou~d /~ not be ~resent at the same time as the reflectors E, E'.
According to this invention, at least t~70 of the beams 7', 7" of the sweeping beam system must have ~heir long ~` cross-section dimensions so oriented that each is at such an angle ~ , ~ , respectively, to the separatio~ direction S that the value of the tangent of that angle i~ g-rea~e~ t~.an the ratio of the minimum projected distance L in the separa- ~ :

.

' ... . . . . .

..
,.. : . . ., ~. i:

- 18d -tion direction to the maximum projected distance M in the transverse direction. The angle just ~entioned must ^ be sufficiently greater so that neither criterion beam can ` be intercepted by more than one reflector at a time, assum-ing either of the "worst case" re~lector arrangements E, E' or F, F' shown in Fig. 12.
; If the system has more than two beams, other beams may be oriented at other angles, but there must always be at }east two beams oriented as just explained, and those two beams are hereinafter referred to as the criterion beamsO
Each of the two criterion beams must of course sweep across a solid angle space in a direction or directions sub-stantially transverse to its long cross-section dimension, but in accordance with the principles of the invention the ;
direction of sweep must-be so chosen that in its sweep (see ~` Fig. 13) each beam moves between intersection with an origin point O which is on one side of the solid angle space and intersection with another point P which is on the opposi~e side of that space and which is spaced in the separation .~; 20 direction S from the origin point. Within this constrain~
it is immaterial whether either beam sweeps from tha origin ~; point 0 to the other poin-t P, or in the opposite direction, ~` or back and forth. The origin point O can be at either side of-the solid angle space, so long as the other point P is ~, 2~ at the opposite side of that space and spaced from it in the separation direction.
~; With the criterion beams oriented and swep-t as ex-plained above, magnitudes are assigned to angular positions of each beam that increase with increasing distance of the beam from its intersection with the origin point O.

: , ~;:

Assu~e, now, that measurements are to be made to reflectors on the two target bodies 10 and 10" in Fig. 2, and that the measurements are to be made with two beams x' and y', as shown in Fig. 5, that have their long dimen-S sions oriented at opposite 45 angles to the horizontal.
- - - The beam y' is shown as sweeping diagonally downwardly at right angles to its long dimension, and the beam x' is shown as sweeping diagonally upwardly, likewise at right angles to i~s long dimension, so that the beams sweep.a 10 -diamond.-shaped space and each beam moves bet~een inter-sec~ion with an origin point at the lef~-hand corner o~ the space swept by the beams and with another point-. . at the right-hand corner of tha~ figure. It is assumed ..
thàt the beams x' and y' are oriented and moved in acc~rdance wit~ ~le principles explained-above and that the reflectors 10, 10" are separated by a minimum possible ~.
distance horizontally and a maximum possible distance . vertically.
`` As t~e beams sweep across the diamond-shaped space, reflections of the beam x' are receiv~d at the mea~urin~
station when it is at its positions designated by xl and .~'` ` X2, ~nd re~lections of the y' ~eam are received when it .
s in its positions designated by yl and Y2l Apart from ~-.
"` . the.principles of this invention, these values, correspond-~ 25 ing to four beam intersections, would imply four possible '.~ . positions for the reflectors 10 and 10", precisely as in }-` the situation illustrated in Fig. 1. However~ because ~` ~ `' ~'`'~ ' ' ' ' ~:`". . ' . .

. -.
: ' .
. ~ ..
.
, .

the orientations and sweep directions of the beams have a known relationship to reflector positions, it is possible to ascertain true reflector positions ~n the situation illustrated~in Fig. 5 by examining the momentary positions of the beams at which reflections were received and com~
paring them for increasing values of the x and y coordin-ates. Observing that the first reflection of the x' beam wàs detected when it was in its sweep position designated by xl, it is evident that no reflector can be present that has a smaller x coordinate than Xi ( that is, to the left of and below the shaded position of the x beam);
and by .the same reasoning it is known that ~here can be no reflector with a y value between zero and-yi (that is, .
in the area above and t~ the right o~ the position of the y' beam that is designated yl). Since a reflection is ~; ` received with the beams in those positions, the reflector producing it could be thought to lie somewhere along the y~ beam in its yl position and somewhere along the x' beam `` .in its Xi position~ But it is known that there is no reflector to the left of the xl/yl position, and neither eam had to move ~o ~he right of that position for a ` :~
-. . reflection to be received from both beams. Hencet it is `~ . unambiguously established that there is a reflector at the -` x;/y; position. Furthermore, there can be no other ; 25 re~lector along the x' beam in its xl p~sition nor along the y' beæm in its yl position because any such other ~` . re~lector would be at less than the minimum possible .i,~ ............................ ' ' ,, . , . ~

.: . !
'`' ' ' ' ' `, ' ' ,~

. .'`' ' ;;` .. , ,' `' .
' , : :, ";'. ' ' . ' , '7~

distance in the horizontal separation direction from the reflector known to exist at xl/yi; and the intersections x2/yi and xl/y2 are thus known to be "empty". The position of the reflector 10 ls thus unambiguously established, and the position of the reflector 10" càn ky similar reaso~ing be unambiguously established at the intersection x2/y2.
- Generally, therefore, the positions of reflectors at the same distance from the measuring station can ~e unam .
biguously determined in a very simple manner, based upon the above described assignment of magnitudes to angular . beam positions. During the scanning sweep of each of i the criterio~ beams, each time a reflection of its radia-tion is received at the measuring station, a value corres-ponding to the momentary angular position of that beam in -15 its sweep is stored. At the con~lusion of a sweep cycle, the positions of the targets from which reflections were received can be unambiguously determined by coupling the `~ values stored for each of those beams during the sweep ~ycle, in the order of their increasing magnitudes -;~ 20 ~i.e., increasing-distance from the origin side), with `~ the respective values stored for the other criterion beam ~` or criterion beams~ taken in the same order.
- Thus, with respect to Fig. S the valwes stored for ~- the x' beam will be x; and x2, and the values stored for :
the y' beam will be yl and Y2. Coupling values from the two sets in the order of ascending magnitudes, lowest-with lowest, highest with-highest, gives reflector positions at xl/yl and x2/y2.

.
.

..
. , -.
;,' ` " , ': , '' ' . ' . :
j~' ' ",, .

Apparatus required for this procedure comprises a logic circuit with a memory having dif~erent memory posi-tions in which are stored the x and y coordinates that correspond to successively received reflections of each criterion beam and from which the coordinates are taken, upon reading of the memory~ in a consistent order of magnitude for every criterion beam.
It will be understood that for the purpose of the herein described coordinate coupling pr~cedure it is no~
necessary that every criterion beam sweep start on ~he or;gin siae of the swe~t space in every sweep cycle, nor ~ven ~hat all criterion beam-sweeps during a single cycle be in the same direction, but mereIy that the magnitude values assigned to angular beam positions be in a con-sistent re~lationship to an arbitrarily chosen originpoint at one side of the swept space. If there are be~ms ` other than the criterion beams, their orientations and directions of sweep ~ay be as desired. It is necessary - that there be an ascertained or ascertainable solid an~le that is swept b~ both criterion beam5 so that a target in ~hat space that gives rise to a reflection of one criteri~n beam will also produca a detected reflection of the other.
~5~ Nevertheless, this does not reguire the criterion beams .,i.~
to have identical cross-sections (i.e., they may have different lengths); much lass is it necessary for the ~i criterion beams to be oriented at right angles to one another or to their respective directions of ~vee~

'-`; - `

. . ~ . . . - . . . .

t~7 A surprising and very important result of orienting and moving the criterion beams in accordance wi-th the principles of this invention is that it becomes possible for adjacent reflectors at equal distances from the measuring station to be arranged at substantially smaller distances apart in the separation direction that the minimum spacing for which the criterion beams are oriented, provided that such reflectors are arranged in accordance with another of the principles of this invention. Thus, ~0 two or more reflectors Gan be mounted rather close to .:
one another on the same side of one and the same object and -- provided they are arranged in conformity with the principle now to be explained -- unambiguous measurements can be made on each of them.
The requirement concerning reflector arrangement :~ applies only to such reflectors as are at substantially - equal distances from the measuring station, that is, such ~` reflectors as cannot be discriminated by range measurements, or range gating. The permissible arrangements of such '~ 20 reflectors in relation to one another are dependent upon the slopes of the criterion beams 7', 7" in relation to ` a ~ine S' ~see Fig. 1~) through the origin point O and thie opposite point P, which line of couse extends in the separation directionO Relative to the line S', the criter-ion beam 7' has the slope ~ and the criterion beam 7" has the slope e. A line K, K' or K" connecting any two reflec~
tors 13F, 13F' or 13G, 13G' or 13H, 13H', respectively, - that are at the same distance from the measuring station must have a slope in relation to the line S' that is out-.
.. ..
. : , . . . , .. . ,:
~, . .
. . , ~ .

6;2~7 - 23a -side the range of slopes between ~ and e, inclusive.
When this requirement is fulfilled as to every such pair of reflectors within the space swept by the criterion - beams, it will be found that every reflector 13 will be the only reflector occupying a region of isolation 17 which is depicted in Fig. 3 and which is related to the orientations of the criterion beams and to the separation direction.

. ~
~` - In the direction of propagation of the beams, the region of isolation 17 has a depth b which is at least .~ , equal to the resolving power of the distance measuring apparatus, that is, at least equal to the smallest incre-~, mental distance to which distance measurements can be made, so that any reflector which is measurably closer to the ;:' 15 measuring station or measurably farther from it than thè reflector 13 will be outside the region of isolation `~ for the reflector 13.

~ .
~ .

~, :

. ' ,;:
';

, , , : . ,: ::, ; :

Z"~'7 - 2~ -Thus, the distance zone within which the region of iso-la-tion lies is defined by a pair of imaginary spherical surfaces which are centered on the measuring s-tation ; and which are spaced equal distances to opposite sides :5 of the reflector 13, the distance between said imaginary `.~surfaces being at least equal to the resolving power .: .
.;value of. the distance measuring apparatus.

Within that distance zone, the region of isolation 17 is defined on the assumption that the two criterion .:10 beams are simultaneously in angular positions of their ~ .~
~sweep such that both are intercepted by the reflector ; 13.. (i.e.r they are assumed to intersect at the reflector), :. and the region of isolation constitutes the part of the .~aforesaid zone that is then occupied by those beams, .. ;

together with that part of sai~ zone that extends between . those beams in the separation direction. The region of ..
.
isolation thus has approximately the shape of an hour-~. . glass with its neck at the reflector 13 that is exclusive `' to it.
It is of no consequence that the region of isolation for a given reflector may contain other surface or ele- :
- ments that reflect radiation generally, the important point being that the particular reflector to which the region is assigned must be the only one therein that can.
produce a reflection of beam radiation that is detectable at the measuring station~ There can be overlap between regions of isolation for adjacent reflectors at ~he same - , ' ~, .

: .. ~' ' , .'.... .. :, .- . , , . ' ., ' :i '`: :
- :: . ~ -, . .

. . . . ~ .

. - 25 -. distance from -the measuring station, provided no reflector intrudes into the region of is~ation for another. If such reflectors are so arranged that each mee~s the require-- ment that it is the only reflector in its region of iso-lation, then unambiguous measurements of reflector positions ;. .
are assured.

Turning back to Fig.~5, it will be seen that even if .: the reflectors 10, lO" are spaced apart by substanti~lly .
.
:~. less th~n the minimum distance in the separation direc-- 10 tion (i.er~ horizontally) with respect to which the beams are oriented, the positions o~ those reflectors can be unam~iguously ascertained if they are arranged in proper : . regions of isolation as just explained. Although th~
.. ~ s.ituation there depicted has caused four beam intersections-15 to be defined, signifying four supposedly possible re~lec-n tor positions, it is known that the reflectors~ 10 and 10"
are arranged in regions of isolation that are matched to the orientation and sweep direction of the beams, and ` accordiAgly two of these four possibie positions axe ~0 established as "empty". The position x2/yl is known to.be impossible becau~e a reflector in any of the other three , . possibla positions would have to be within the region o~ .
. .
." isolation of tha~ ona reflector, and therefore it would . ~ave to be the only reflector in the swept space, whereas 25 it is known that a least two reflectors are present. By similar reasoning it can be known that no reflector can be present at the position designated xl/y~. .;

,-' ` ` . '' `' : : '' ` ... . . .

~ , ! , ,, " ~, ,`.'. i ,: ' ` . ` :' ' . . ' .' '.': ; ' ` , i' 1 . ` ' . '` ,' .', ' `,, ` ~.' . , ' ' ~ 7t~

- Since there is an interdependent relationship between .~ beam orientation and sweep direction on the one hand, and :. the configuration of the regions of isolation on the other . hand, either can be taken as the starting point in the design of a measurement system according to the invention~
-.- If the distribution o~ target reflectors can be con-.- trolled only to the extent that it is possibla to ascertain ` . directions of probable maximum and minimum separation and ; probable "worst case" separations in ~hose directions, then 10 .orienta.tion and sweep direction of the criterion beams can be established on the basis of that information~ as explained bove. Note t~at if the "worst case" distribution o re-. flectors for which the beam arrangement is established is in fact the worst distribution ever encountered, then every re1ector will always be in its own unviolated regionof isolation 17.
If the distribution of target reflectors is more close-ly controllable, so that an hourglass-shaped region of iso- -~ation 17 can be defined and maintained for each reflec~or of every pair of adjacent reflectors that are at the same distance from the measurin~ station, all such regions ~eing of like shape, then the criterion ~eams can be o.riented by reference to that reyion of isolation.
- Speciflcal1y, the orientation of the long dimensions o~ the criterion beams must be such that those two beams, if th~y were simultaneously intersecting the target 13, would lie within its region of isolation-17. Preferably, as shown ;~
in Fig. 2, the criterion beams would be oriented to have , ~, .
. . . . .
. : ., ................. ~ . , - ,.

` - 27 -their long dimensions 8', 8" parallel to t~e diagonal boundaries of the region of isolation 17. The directions ~ . .
of sweep of the criterion beams will ~e so chosen that each will cross the reflector in movement from one to . r ;~- 5 the other of the "permitted" zones laterally adjacent to its region of isolation.
Under certain conditions it is advantageous for the .: .
beams ta move in a fixed relationship to one another like that shown in Fig~ 7. This permits the mechanism of the deflection de~ice 11 to be substantially simplified. I~
~` ; the arrangement shown in Fig. 7, th~ two beams ~5 and 26 ;~ have their long dime~sions oriented at different angles ;` oblique to the`horizontal, and they sweep horizonta~ly, as denoted by arrows 27, both always in the same horizontal direction and in a fixed spaced relation to one another~
` Because both beams sweep horizont`ally, it will be apparent that the solid angle or space that they ~ointly sweep can .
be substantially elongated horizontally~ as denoted by the shaded area in Fig. 7, making the arrangement especially ` 20 suitable for measurements on target bodies confined to the surface o~ land or waterO However, with this arrangement `` ~here are spaces 28~ 29 that are swept, in each case, by `- only one o the two beams. A target in one of those spaces would therefore give rise to only one reflec~ion ~uring a .
beam sweep cycle, and calculation of target positions, although possible, might be complicated. Therefore, to simpliy calculations, it is desirable that the optical system be provided with a shield, preferably placed in an , i ' ;
.;' ' ' : : :, : . ,: ~.,., : ~

2r7~7 intermediate image plane, for masking off the spaces 28 and 29, thus ensuring that a reflection from a targe-t will be received for every beam ~7henever a reflection i~ received .. from any beam.
- 5 If the beams make their sweeps successi~ely, the detector 4 can comprise a single channel, but if two or -~ more beams make their sweeps simultaneously, the deteckor .~ will have a channel for each such beam or the respective beams will be pulsed at different timRs~
With the arrangement as shown in Fig. 7, wherein the : beams 25 and 2~ make their sweeps simultaneously, reflections `from either beam might be detected at the measuring station . . .
- 2 by the detector channel associated wit~ the other beam.
- To prevent this, as shown in Fig. 6, the channels of ~he detector 4 at the measuring station 2 can have ~ields of response or scanning windows 30, 31 which are substantially matched to the cross-section shape and size of the respec-tive beams 25 and 26 with which the channels are associated and wnich move with their associated beams~ Fig~ 6 repre-- 20 sents the beams 25 and 26 and their respective fields of 'I
xesponse 30 and 31 as seen in cross-section at an arbitrary distance in front of the measuring station 2, The restricted scanning windows or fields of response 30 and 31 afford the further advanta~e o improving the 25 signal-to-noise relationship and consequently a~ording ::
a greater sensitivity an~ distance range than would be ~he càse if the detector 4 had a single field of reception that . covered both beams or the entire space swept by the beams.
.

,. ' ,' ~'~

:. - 29 -. When the spaces 28 and 29 that are swept by less than all of the beams are not masked off, unambiguous measure-; ments of reflector locations can be made by logical analysis.
: Fig. 8 illustrates a situation in which several reflectors ; 5 A-E are arranged in more or less horizontal alignment -~ with one another, and the figure indicates successive momentary angular positions of each of the~beams 25 and 26 of Figs. 6 and 7 at instants when reflections of their radiation, returned fxom the several reflectoxs, are .. }o detected at tha measuring station. If, within the portio~
of the solid angle that is swept by both beams, one beam has a target intercepting position at which it has only one point of intersection with the other beam, then that ; point of intersection desi~nates a valid target which is unambiguously ascertained, and the positions of the other targets can be unambiguously ascertained by logic. Thus, in Fig.-8 the beam 25, when it intersects the target D, is in a position in which it makes only one intersection with ::
the beam 26. It follows that the indicated position of target D is a real target position, and targets cannot .
exist at the beam intersection positions th~t are above and between targets C and D and below and bet~een targets . . ~ , .
D and E. Elimination of the impossible ta~get positions . de~ined by the last mentioned beam intersections enables the real positions of targets C and E to be unambiguously "~ ascertained, and so on, using the same reasoning as was . ~ :
~.`; employed in connection with Fig. 5.
`' ' '':
.~ , ' ` ' , ~
, . ;

. , : i . , , ~
- ; .. ,. :., . ..

.. : ,~.. ~;. . , 1`' If targets within the swept space are so close to one another that no such starting point as used in the last example is expectable, and if for some reason it is considered undersirable to mask the portion or portions of the solid angle swept by only one beam, then it is possible to employ the arran~ement shown in Fig. 9, usi~g three beams 34, 35, 36, each having its long dimension at an angle to that of each of the others and all havin~ .
movement in the separation direction with respect to an origin point. ~ere~ a region of isolation for each reflec-tor, such as is illustrated in Fig. 3, has its ~oundaries deined by any two of the beams, on the a~sumption ~hat those two criterion beams are simultaneously in positions of their angular motion such t~at both are intercepted by the reflector for the region o~ isolation. Thus.the re~ion of isolation could b defined by reference to the cross-sections of the two outer beams 34 and 36 r and the region of isolation illustrated in Fig. 3 would be so configured tha~ the cross-sections of those two beams would lie ~holely ~0 within the boundaries of its oblique side planes 20' 20"
and 1~' ~ 19". Alternatively, the middle beam 35 and eit~er of tXe outer beams 35 or 36 could define the boundaries of a narrower reyion of isolation, that i5, one having a smaller angle.between its oblique side planes 20' - 20" :~
.
.: 25 and 19' - 19". In principle, such reduction o~ the width of the region of isolation would be advantageous insofar as it would facilitate identification of "emp~y" beam ' . , '~

:;. -.~ ' ' ' . .

.~............. , , ; . . .

- . : , :, .: ~ : :

- 31 ~
intersection points which do not designate locations of real targets, but it would have the disadvantage of per-mitting adjacent reflectors to ~e closer to one ano.her and thus limiting the possibility for discrimination between them.
Fig. 10 illustrates how beam inters~ctions corres-ponding to real reflectors can be distinguished from "empty" intersections when three beams are used. As shown in Fig. 10, reflectors a~ b and c, which are assumed to be at equal distances from the measuring station, lie along a line extending generally in the direction of sweep of three beams oriented generally like the beams 34, 35, 36 of-Fig. 9. Both above and below the points of beam intersectio~ ~hat are deflned by re~lectors , ` 15 -a, b and c there are points at which all three beams intersect to signify apparent reflector positions. To distinguish real reflector positions from l'empty" ones, the scheme of beam intersections is examined for a valid one at which all three beams intersect. By reasoning like that applied in ~onnection with Fig. 3, is is eviden~ that reflector a is at such a position and ~hat there must be a real reflector at that position. It ~ollows tha~
positions d and e must be "empty" positions, since ref~ec-tors at those positions would be within the region of isolation of the reflector a, and from this! in turn, the positions of reflectors b and c are unambiguously ascer~
tained. ;
.` . . . .

.. "
. . . ..
.. . . . ..... . .
.~ . , , ; ,, ., .. , ~ :
. ., . ,,: , . ..
:, - . ,, . . ~: . ~. . ..

32 ~
In some cases it may be advantageous to employ a beam system such as is illustrated in ~ig. 11, comprising - four beams 37 having their long cross-section dimensions so oriented that if they in~ersected simultaneously at a point they would define a symmetrical star-shaped pattern.
In this case, all of the bea~s are swept in the sa~e direc-tion. Thus, assuming that all of ~he beams in Fig. 11 were swept hori~ontally, measurements made with the 'edgewise-sweeping horizontally oriented beam would be to disregarded because they would be meaningless. The region of isolation or each reflector would be matched to the orientations of a selected pair of cri~erion beams and in this case would be either 45 or 90. The advantage o~ the beam arrang~ment of Fig. 11 is that it permits any desired orientation of the beam system and its sweep direction, so that it can be readily converted from one '' application to another in which conditions are different. ' From the foresoing description taken with the accom-panying drawings it will be apparent th~t this invention ' provides a method and means for employing angularly sweep-ing ,fan shaped beams of radiation for unambiguous deter-, mination of the positions of reflectors in the space ,' ~wept by the beams that are at equal distances from a ,', measuring station from which the beams are emitted. ' -.~ 25 The invention is defined by ~be following claims: ' .~" ' ; .

. -- . .
'' '" , '' ' . ' ' '~

. ~ " , ~,~ ."s ;; , , , ~ " , . ,,,, , :, " , ~ ~ ,

Claims (13)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of unambiguously determining the position of each of a plurality of reflectors in relation to a measuring station at the apex of a solid angle space in which the reflectors are located and from which radiation is emitted into said space, each of said reflectors being of the type whereby intercepted radiation is reflected in the direction directly opposite to the one from which it arrived at the reflector, and the reflectors being so dis-tributed in said space that adjacent reflectors at equal distances from said station are always separated by at least a minimum projected distance in a separation direc-tion and by no more than a maximum projected distance in a direction transverse to said separation direction, said method being characterized by A. emitting said radiation in the form of at least two fan-shaped beams, each of which has a long cross-section dimension and a short cross-section dimension, said long dimension of each of said at least two beams being oriented (1) at an angle to that of the other and (2) at an angle to said separation direction which is such that its tangent value is greater than the ratio of said maximum distance to said minimum distance; and B. sweeping each of said two beams in a direction such that each of them moves across said space between intersection with an origin point at one side of said space and intersection with another point which is at the opposite side of said space and which is spaced in said separation direction from said origin point.

2. The method of claim 1, further characterized by:
C. assigning magnitudes to angular positions of each beam that increase with increasing dis-lance of the beam from said origin point.

3. The method of claim 2, wherein said measuring station comprises a detector by which beam radiation reflected back to said measuring station by a reflector can be detected, further characterized by:
D. each time a reflection of radiation of one of said two beams is detected at the measuring station, storing the magnitude of the then-existing angular position of the beam; and E. unambiguously ascertaining the position of each reflector from which reflections were received during a sweep cycle by coupling stared values.
for one of said two beams, taken in the order of their magnitudes, with those for the other of said two beams, taken in the same order.

4. A method of ascertaining, by means of radiation emitted from a measuring station, the locations relative to said station of reflectors that are remote thereform and towards which the radiation is emitted, each of said reflectors being of a type that reflects said radiation in the direction directly opposite to that from which it arrived at the reflector, and said radiation being emitted in fan-shaped beams, each having a long dimension and a transverse short dimension, both transverse to the direction of beam pro-pagation, every beam being swept angularly across a solid angle space that has the measuring station at its apex so that momentary reflections of its radiation can be de-tected by detector means at said measuring station, said method being characterized by:
A. orienting said long dimension of each of said beams at an angle to that of every other;
B. sweeping each of at least two of said beams substantially transversely to its said long dimension in a direction such that each moves across said space between intersection with an origin point at one side of said space and intersection with another point which is at the opposite side of said space and which is spaced in a separation direction from said origin point; and C. maintaining such relationship between the two reflectors of every pair thereof in said space that are at substantially equal distances from said station that each of such reflectors is in a region from which the other is excluded and which comprises the part of said space that would be occupied by said two beams if they were simul-taneously in positions of their respective sweeps at which both were intercepted by that reflector, together with the part of said space that would extend between the beams in said separation direction.

5. The method of claim 4 wherein said two beams have their long dimensions at equal and opposite angles to a plane which extends in said separation direction and bisects the apex angle of said solid angle space.

6. The method of claim 5 wherein radiation is emitted in a third beam which has its said long dimension at an angle to that of each of said two beams and moves across said space from intersection with one of said points to inter-section with the other of them.

7. The method of claim 4, further characterized by:
D. at the measuring station, masking the portions of said solid angle space that are swept by only one of said at least two beams, so that reflec-tions from reflectors in said portions of said space cannot be detected by said detector means.

8. The method of claim 6, further characterized by:
at the measuring station, masking the portions of said solid angle space that are swept by less than all of the beams so that reflections from reflectors in said portions of said space cannot be detected by said detector means.

9. The method of claim 4 wherein angular positions of each of said two beams are assigned magnitudes that increase with increasing distance of the beam from said origin point, further characterezed by:

D. each time a reflection of radiation of one of said two beams is detected by said detector, storing the magnitude of the then-existing angular position of that beam; and E. unambiguously ascertaining the position of each reflector from which reflections of each of said at least two beams have been detected by said detector by coupling stored values for one of said two beams, taken in the order of their magnitudes, with those for the other of said two beams, taken in the same order.

10. The method of ascertaining at a measuring station, by means of radiation emitted therefrom and reflections thereof detected by a detector at said station, the locations relative to said station of reflectors towards which the radiation is emitted and each of which is of a type that reflects radiation directly oppositely to the direction from which it arrived thereat, said radiation being emitted from said station in fan-shaped beams, each having a long cross-section dimension and a narrow cross-section dimension transverse to its said long dimension, each having its said long dimension oriented at an angle to that of every other beam, and each being swept angularly, substantially transversely to its said long dimension, across a solid angle space that is swept by every other beam and has the measuring station at its apex, said method being characterized by:

A. sweeping at least two beams in directions such that each moves between its intersection with an origin point at one side of said space and its intersection with another point which is at the opposite side of said space and is spaced in a separation direction from said origin point, so that the momentary angular positions of each of said beams can be assigned values that increase in magnitude with increasing distance from said origin point;
B. maintaining, as between the reflectors of every pair thereof in said space that are at substan-tially equal distances from said station, a relationship such that each of such reflectors is in a region from which the other is excluded and which comprises the part of said space that would be occupied by said two beams if they were simultaneously in positions of their respective sweeps at which both were intercepted by that reflector, together with the part of said space that would extend between said beams in said separation direction;
C. each time a reflection of radiation of one of said at least two beams is detected at said detector, storing the value of the then-existing angular position of that beam; and D. after each of said at least two beams has made at least one sweep across said space, unambig-uously ascertaining the position of each reflector from which reflections were detected by coupling the values stored for each of said at least two beams, taken consistently in order of magnitudes, with those for the other of said two beams taken in the same order of magnitudes.

11. The method of claim 10, wherein the reflectors are carried on the earth's surface, further characterized by:
(1) each of said two beams having its said long dimension at an angle to the horizontal; and (2) each of said two beams being swept substantially horizontally.

12. Apparatus by which the position of any one of a plur-ality of reflectors can be unambiguously determined in relation to a measuring station at the apex of a solid angle space in which the reflectors are located, each of said reflectors being of the type whereby intercepted radiation is reflected in the direction directly opposite to the one from which it arrived at the reflector, and the reflectors being so distributed in said space that adjacent reflectors at equal distances from said station are normally separated by at least a minimum projected distance in a separation direction and by no more than a maximum projected distance in a direction transverse to said separation direction, said apparatus being of the type comprising a radiation emitter at the measuring station for emitting a plurality of fan-shaped beams of radiation, each of which has a long cross-section dimension and a short cross-section dimen-sion, said emitter being arranged to sweep each beam angularly, substantially transversely to its said long dimension, across said solid angle space, said apparatus being characterized by:
said emitter being further arranged A. to emit at least two of said beams with their said long dimension oriented (1) at an angle to one another and (2) at an angle to said separation direction which is such that its tangent value is greater than the ratio of said maximum distance to said minimum distance; and B. to sweep each of said two beams in a direction such that the beam moves between intersection with an origin point at one side of said space and intersection with another point which is at the opposite side of said space and which is spaced in said separation direction from said origin point.

13. The apparatus of claim 12, wherein the slope of said long dimension of one of said beams relative to a separation direction line connecting said points has a first value and the slope of said long dimension of the other of said beams relative to said line has a second value, further characterized by:
said reflectors being so arranged that a line through any two reflectors that are within said space and at substantially equal distances from the measuring station has a slope in relation to said separation direction line that is outside the range of values which lies between and includes said first and second values.