GB1605201A

GB1605201A - Target tracking arrangements

Info

Publication number: GB1605201A
Application number: GB825178A
Authority: GB
Original assignee: Elliott Brothers London Ltd
Current assignee: Allard Way Holdings Ltd
Priority date: 1978-03-02
Filing date: 1978-03-02
Publication date: 1983-05-25

Description

(54) IMPROVEMENTS IN OR RELATING TO TARGET TRACKING ARRANGEMENTS (71) We ELLIOTT BROTHERS (LONDON) LIMED, a British Company, of Marconi House, New Street, Chelmsford, Essex CMl lPL, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to target tracking arrangements.

As is known, one approach to tracking a target is to provide a view of the target, by infra-red, television or other means on a display and to monitor the extent of control necessary in order to maintain the position of the target within the display.

In other cases it is required to generate control signals which will actually physically control the aim of the imaging system of the arrangement in order to ensure that the display follows a particular target.

In such arrangements, if these are to be automated, the need arises for what is commonly called an automatic picture monitor which will provide monitoring signals relating to movement of, or within, the display.

One object of the present invention is to provide an improved target tracking arrangement.

According to this invention, a target tracking arrangement comprises means for selecting a patch (hereinafter referred to as the "inner patch") of a display area, means for sampling said inner patch in a plurality of elemental areas, means for storing signals representative of the brightness of the elemental areas of said inner patch, means for sampling at a later time, the display within a larger patch (hereinafter referred to as the outer patch) encompassing said inner patch in a plurality of elemental areas, means for comparing, area by area the elemental areas of said inner patch with re spective corresponding elemental areas of said outer patch for one possible position of said inner patch within said outer patch to produce at each comparison a signal of amplitude re lating to the degree of correspondence between compared elemental areas, means for applying all of said produced signals for one possible position of said inner patch within said outer patch to an accumulative store and means for comparing the result stored in said accumula tive store with the result stored in other accumulative stores in respect of corresponding comparisons carried out in respect of other possible positions of said inner patch within said outer patch to provide an indication of the movement of said inner patch within said outer patch and thus an indication of the movement of any target encompassed by said inner patch.

Said elemental brightness signals may be quantised or, whilst not preferred, both quan- tised and digitised.

Preferably said accumulative stores and sak means for storing signals representative of tW brightness of elemental areas are realised by charge coupled devices (C.C.D.'s).

Preferably said means fortsampling comprises a C.C.D. or similar imaging device.

Preferably again said signals produced as a result of the comparison of elemental areas are in binary form, that is to say a binary "I" 0r a binary "0" is produced is dependence upon the degree of co-incidence between compared elemental areas.

Typically said inner patch is sampled in a rectangular array of elemental areas, twelve by eight, and said outer patch is sampled in a rectangular array of elemental areas, sixteen by twelve.

The invention is illustrated in and further described with reference to the accompanying drawings in which, Figures 1 to 7 are explanatory daagcsnas, Figure 8 is a simplified circuit diagram of a picture matching arrangement in accordance with the present invention.

Referring to Figure 1, this illustrates a target selected in a television automatic tracking r" system for a missile. As will be seen the target is a fighting tank. The aiming point of the miS sile is shown at 1 and a television "auto lock follow" (ALF) system is provided on the mist sile to provide a tracking facility. To be effective the aiming point I is required to be main- tained on the boresight of the television camera.

To enable this to be done, motion of the aiming point 1 together with a relatively small surrounding portion of the target lying within what will hereinafter be called an "inner patch" 2 is monitored with respect to a larger area 3, which will hereinafter be referred to as an "outer patch". From this can be derived motion of the aiming point 1 relative to the camera boresight.

Where the missile tracking system requires the actual presentation of a television picture, normally an area larger than the inner patch 2 will be displayed.

In order to maintain the aiming point 1 on boresight the extent and direction of the relative motion of the inner patch 2, from the television frame in which it was selected to a subsequent television frame is detected by comparing the inner patch as selected with the outer patch in that subsequent frame in order to generate signals indicative of the relative movement of the inner patch 2 within the outer patch 3.

The comparison technique employed will now be described with reference to Figures 2 to 7.

The image within the inner patch 2 derived during that television scan in which the inner patch is selected is sampled by a C.C.D. imaging device in 96 elemental areas (in a matrix of 12 x 8) so that for each elemental area an analogue signal sample is provided which represents the mean density or contrast within that elemental area. Such a technique is well known per se.

The position of the inner patch is determined by the selection of a desired aiming point, again as known per se. The information derived as a result of sampling the inner patch 2 is stored in an inner patch store.

In each subsequent television frame the image within the outer patch 3 is similarly sampled, but in 192 elemental areas (a 16 x 12 matrix), each elemental area in the outer patch corresponding in size to each elemental area in the inner patch.

The said outer patch sampled information is first passed through a picture matching device such as the one shown in Figure 8 and described below. The sampled information relating to the outer patch is stored temporarily in an outer patch store.

The inner patch 2 is compared in the picture matcher with the outer patch 3, element by element in order to determine the location of the inner patch within the outer patch which gives optimum match.

It will be noted that the elemental areas in the inner patch 2 shown in Figure 2 have been numbered 1 to 96, whilst the elemental areas in the outer patch 3 shown in Figure 3 have been numbered 1 to 192. A series of 25 groups of comparisons then takes place as graphically illustrated in Figures 4 to 7, where the inner patch 2 is shown overlaid upon the outer patch 3.

In the first comparison group, as represented by Figure 4, the comparisons are as follows: Inner Patch 2 Outer Patch 3 elements 1 to 12 elements 1 to 12 elements 13 to 24 elements 17 to 28 elements 25 to 36 elements 33 to 44 elements 37 to 48 elements 49 to 60 elements 49 to 60 elements 65 to 76 elements 61 to 72 elements 81 to 92 elements 73 to 84 elements 97 to 108 elements 85 to 96 elements 113 to 124 In the second comparison group, as represented by Figure 5 the comparisons are as follows:: Inner Patch 2 Outer Patch 3 elements 1 to 12 elements 2 to 13 elements 13 to 24 elements 18 to 29 elements 25 to 36 elements 34 to 45 elements 37 to 48 elements 50 to 61 elements 49 to 60 elements 66 to 77 elements 61 to 72 elements 82 to 93 elements 73 to 84 elements 98 to 109 elements 85 to 96 elements 114 to 125 In the third comparison (not illustrated) the inner patch 2 is moved one further step to the right (as viewed) compared to its position in Figure 5 and so on until the inner patch 2 reaches the extreme top right hand corner of the outer patch 3. The inner patch 2 is then returned to the left hand side of outer patch 3, but moved downwards by one row of elemental areas in the outer patch 3. This represents the sixth comparison group as represented in Figure 6.In the seventh comparison group the comparisons are: Inner Patch 2 Outer Patch 3 elements 1 to 12 elements 17 to 28 elements 13 to 24 elements 33 to 44 elements 25 to 36 elements 49 to 60 elements 37 to 48 elements 65 to 76 elements 49 to 60 elements 81 to 92 elements 61;to 72 elements 97 to 108 elements 73 to 84 elements 113 to 124 elements 85 to 96 elements 129 to 140 The comparison groups then continue until every position of the inner patch 2 within the outer patch 3 has been covered. The final comparison group, with the inner patch 2 at the extreme bottom right hand corner of the outer patch 3, is as illustrated in Figure 7. This is the 25th comparison group with comparisons as follows: Inner Patch 2 Outer Patch 3 elements 1 to 12 elements 69 to 80 elements 13 to 24 elements 85 to 96 elements 25 to 36 elements 101 to 112 elements 37 to 48 elements 117 to 128 elements 49 to 60 elements 133 to 144 elements 61 to 72 elements 149 to 160 elements 73 to 84 elements 165 to 176 elements 85 to 96 elements 181 to 192 At each comparison of an elemental area in the inner patch with an elemental area in the outer patch, a binary signal is generated which depends upon the levels of the two signal samples representing the brightness or contrast of the elemental areas. Thus if both of the compared elemental areas are similar within a small error allowance e (which may be either adjustable or preset) the result of comparison will be a binary 1.On the other hand, if the elemental areas are dissimilar by more than the allowance e the result will be a binary zero.

At each complete comparison stage the results of each comparison at elemental area level are added together in an integrating store.

The total in this last mentioned store will have a value which represents the degree of co-incidence between the inner and outer patches for that one group of comparisons.

Similar measures are provided for the remaining of the twenty five groups of comparisons so that for each group of comparisons a total is stored representative of the degree of co-incidence between the inner and outer patch at that group of comparisons.

The twenty five totals may then be compared and the highest selected. This will identify the stage of comparison at which the best picture match was obtained and thus the position of the inner patch 2 relative to the outer patch 3 at that stage of comparison.

From this, control signals are generated for use in controlling the position of the outer patch in the next television frame and/or the aim of the television camera to restore the target to boresight and/or the directional controls of the missile to guide it towards the target.

Referring to Figure 8, this is a schematic diagram of one picture matching arrangement in accordance with the present invention for carrying out the comparison functions above described. Throughout this diagram, C.C.D.

clocking arrangements have been omitted for clarity. A C.C.D. imaging device 4 is provided to generate the sampled signals representing the elemental areas of the outer patch.-The last mentioned signals are applied to a 69 stage serial store 5 and are clocked progressively therethrough. Each of 25 selected stages of the serial store 5 is connected to the input of an individual one of twenty five comparison circuits 6. The 25 selected stages are grouped in five groups of five adjacent stages, each group being separated from the next by eleven untapped stages of the register.

Each comparison circuit 6 has a second input connected to the output of an inner patch store 7. Inner patch store 7 is provided to store quantised signals representing the elemental areas of the selected inner patch and is arranged to output these sequentially. Signals appearing at the output of the inner patch store 7 are applied to all of the second inputs of the comparison circuits 6 simultaneously. The application of elemental inner patch signals to the comparison circuit 6 is synchronised to the clocking of the outer path sampled signals through the register 5 so that, in sequence, the comparison groups already described with reference to Figures 4 to 7 takes place. Thus the comparator (referenced 6') connected to the last stage of register 5 derives successively the results of the comparisons carried out in comparison group 1.The output of this last mentioned comparator is connected to one portion, referenced 8' of a C.C.D. (charge coupled device) output shift register 8. The comparator (referenced 6"), connected to the second-to-last stage of the register 5, will obtain the results of the comparisons carried out in the second cont- parison group described above. The output of this last mentioned comparator 6" is connected to a further portion, referenced 8" of the C.C.D. shift register 8. The C.C.D. register 8 contains twenty five stages each connected to a different one of the twenty five comparators 6 and each receiving all of the comparison results of a different one of the twenty five comparison groups.

A third input (not shown) is provided in parallel to all twenty five comparator stages.

This is used to strobe the comparators when- ever the outer patch information in register 5 is in a position to provide valid comparison results as required in the twenty five groups listed above. Invalid conditions related to the borders of the outer patch would otherwise corrupt the wanted information. The comparator output representing a binary "one" is a charge packet whose magnitude is about one hundredth of the saturation charge level of the corresponding output shift register stage. A binary "zero" is represented by an empty charge packet. Thus each portion of the C.C.D.

shift register 8 will accumulate a total signal depending upon the degree of picture matching in the comparison group with which it is associated. The output of store 8 is connected via an output amplifier 9 to an output terminal 10 at which appears timed analogue signals representing the required picture match information.

In order to select a required inner patch, terminal 10 is connected to a micro-processor (also not shown) from which control signals are derived for controlling the aim of the television camera and/or the missile as well as the position of the outer patch in the next T.V. frame, in dependence upon the determined relative motion of the inner patch 2.

Having traversed register 5, signals corresponding to the elemental areas of the outer patch are applied to the input of a serial store 11, which may be termed "the outer patch store". The output of the store 11 is applied to a transfer gate 12, the output of which is connected to an analogue refresh circuit 13, which in turn is connected to the input of the inner patch store 7.

The inner patch is selected as required by controlling the transfer gate 12. Once selected, signals representative of the elemental areas of the inner patch are circulated in a path which includes inner patch store 7, transfer gate 12 and analogue refresh circuit 13. In order to up date the signals corresponding to the elemental areas of the inner patch stored in inner patch store 7, switch 12 is operated for a given part of each field in order to provide access to inner patch representative signals which are passing through store 11 as a part of the total outer patch signal information. This last mentioned information is of course freshly obtained from the register 5 and the C.C.D. imaging device 4.

If required, a more complex switching function may be provided for gate 12 to merge selected percentages of inner and outer patch information as required, to form the new inner patch.

The analogue refresh circuit 13 is a multilevel quantising circuit which maintains the inner patch information with a defined number of levels and prevents it becoming corrupted by accumulated "dark current" and noise from the inner patch store 7.

WHAT WE CLAIM IS: 1. A target tracking arrangement comprising means for selecting a patch (hereinafter referred to as the "inner patch") of a display area, means for sampling said inner patch in a plurality of elemental areas, means for storing signals representative of the brightness of the elemental areas of said inner patch, means for sampling, at a later time, the display within a larger patch (hereinafter referred to as the outer patch) encompassing said inner patch in a plurality of elemental areas, means for comparing, area by area the elemental areas of said inner patch with respective corresponding elemental areas of said outer patch for one possible position of said inner patch within said outer patch to produce at each comparison a signal of amplitude relating to the degree of correspondence between compared elemental areas, means for applying all of said produced signals for one possible position of said inner patch within said outer patch to an accumulative store and means for comparing the result stored in said accumulative store with the result stored in other accumulative stores in respect of corresponding comparisons carried out in respect of other possible positions of said inner patch within said outer patch to provide an indication of the movement of said inner patch within said outer patch and thus an indication of the movement of any target encompassed by said inner patch.

2. An arrangement as claimed in Claim 1 and wherein said elemental brightness signals are quantised.

3. An arrangement as claimed in Claim 1 or 2 and wherein said elemental brightness signals are both quantised and digitised.

4. An arrangement as claimed in any of the above Claims and wherein said means for sampling comprises a C.C.D. or similar imaging device.

5. An arrangement as claimed in any of the above Claims and wherein said signals produced as a result of the comparison of elemental areas are in binary form, that is to say a binary "1" or a binary "0" is produced in dependence upon the degree of co-incidence between compared elemental areas.

6. An arrangement as claimed in any of the above Claims and wherein said inner patch is sampled in a rectangular array of elemental areas, twelve by eight, and said outer patch is sampled in a rectangular array of elemental areas, sixteen by twelve.

7. A target tracking arrangement substantially as herein described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. through store 11 as a part of the total outer patch signal information. This last mentioned information is of course freshly obtained from the register 5 and the C.C.D. imaging device 4. If required, a more complex switching function may be provided for gate 12 to merge selected percentages of inner and outer patch information as required, to form the new inner patch. The analogue refresh circuit 13 is a multilevel quantising circuit which maintains the inner patch information with a defined number of levels and prevents it becoming corrupted by accumulated "dark current" and noise from the inner patch store 7. WHAT WE CLAIM IS:

1. A target tracking arrangement comprising means for selecting a patch (hereinafter referred to as the "inner patch") of a display area, means for sampling said inner patch in a plurality of elemental areas, means for storing signals representative of the brightness of the elemental areas of said inner patch, means for sampling, at a later time, the display within a larger patch (hereinafter referred to as the outer patch) encompassing said inner patch in a plurality of elemental areas, means for comparing, area by area the elemental areas of said inner patch with respective corresponding elemental areas of said outer patch for one possible position of said inner patch within said outer patch to produce at each comparison a signal of amplitude relating to the degree of correspondence between compared elemental areas, means for applying all of said produced signals for one possible position of said inner patch within said outer patch to an accumulative store and means for comparing the result stored in said accumulative store with the result stored in other accumulative stores in respect of corresponding comparisons carried out in respect of other possible positions of said inner patch within said outer patch to provide an indication of the movement of said inner patch within said outer patch and thus an indication of the movement of any target encompassed by said inner patch.