GB2247585A

GB2247585A - Tracking an object

Info

Publication number: GB2247585A
Application number: GB9018710A
Authority: GB
Inventors: Peter Caleb Frederi Wolfendale
Original assignee: AUTOMATIC SYST LAB Ltd
Current assignee: AUTOMATIC SYST LAB Ltd
Priority date: 1990-08-25
Filing date: 1990-08-25
Publication date: 1992-03-04
Also published as: GB9018710D0

Abstract

A method and apparatus for tracing and locating the varying position of a mobile object relative to an origin. The position is established by measuring spatial angles between a reference direction which is fixed relative to the origin and a first and second line of sight of prescribed radiation transmitted from the mobile object. <IMAGE>

Description

TRACKING AN OBJECT This invention relates to a method of, and apparatus for, establishing the position of a remote object.

According to the present invention there is provided a method of tracking and logging the varying position of a mobile object relative to an origin, by measuring the spatial angles of first and second lines of sight of prescribed radiation between the mobile object and a reference direction which is fixed relative to the origin, the first line of sight extending between a first radiation transmitter and a first radiation receiver, and the second line of sight also extending, but at an angle to the first line of sight, between a radiation transmitter and a radiation receiver, the transmitted radiation being modulated and the or each radiation receiver being tuned to said modulation so as to discriminate between background radiation and the prescribed radiation, the method-including the steps of calculating the position of the object from a measurement of the said angles, and recording the calculated positions in material form.

Conveniently, the radiation is visible radiation and the or each detector is an optical detector steered by servo drives. The detectors are programmed to recognise the specific modulation of the light source from all background visible radiation. The modulation could be amplitude modulation (flashing the light) or a positional modulation such as a small cyclic movement around the basic position of the light source.

The detector element in each steerable detector system could be akin to a television camera with photoelectric equipment capable of responding to an image focussed by the optical systems. Alternatively, a four quadrant photocell could be used to indicate when the image of the light spot departs from an origin at the centre of the four quadrants, any such detected discrepancy prompting appropriate drive signals to servo motors to adjust the direction of the optical detector system so as to restore the image to the required origin position on the photocell.

In one embodiment, the remote object would be a vehicle, located for example within a given area, for example, a square of ground with side 1 km. Two detectors placed about 1 km apart from each other would be capable of locating the target within such a square, by triangulation techniques. Of course, if ever the object were to lie on a line between the two detectors, a third detector would be needed in order to establish its position uniquely.

For a better understanding of the present invention, and to show more clearly how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawing which is a sketched perspective view of one embodiment of the tracking system of the invention.

In the drawing, a wheeled vehicle 10 carries a flashing light 11 which emits visible light 12. A first telescope 13 directs light from the light source 11 on to a first four quadrant photocell 14 and output signals from the photocell 14 are passed along first input line 15 to a controller 16. This is receptive to data delivered along the line 15 indicative of a discrepancy between the position of the image of the light source 11 on the photocell 14, and the origin of the photocell 14. Any such discrepancy prompts the generation of output signals along one or both of command lines 17 and 18. Line 17 commands a first azimuth control motor 19 and line 18 commands a first elevation control motor 20. These motors control the direction of telescope 13 in azimuth and elevation respectively.

In like manner, some of the radiation 12 is directed by a second telescope 23 onto a second four quadrant photocell 24 and signals from the photocell are delivered by line 25 to the controller 16. Second command lines 27 and 28 actuate second azimuth control motor 29 and elevation control 30. Processor 16 delivers to store 31 along output line 32 data representative of the position of the vehicle 10 on the ground relative to the fixed positions of the telescopes 13 and 23.

In one application of the system, the vehicle 10 can be caused to move in a specified pattern of movement over the area in question, for example, to take ground samples at known points within the area. This would be useful in a case of radiactive contamination of a ground area, when a multitude of samples has to be taken, and the position of each known with a high degree of certainty.

In other embodiments, radiation could be brought onto the focal plane of a fixed orientation telescope by the use of steerable mirrors, the controller 16 computing the position of the light source 11 from the positions of the steerable mirrors.

In other embodiments, the relative position of the light and detector can be reversed so that a steerable detector may be carried on the vehicle, and two or more fixed light sources, each with suitable modulation, observed in sequence by the same detector.

A further variation is to have an array of lights fixed relative to each other, each of which has a unique and recognisable modulation. In this manner one or more detectors may align to each in turn and measure the relative angular orientation of each. Since the spatial relationship of each light is known, it is possible to determine the distance between light and detector by a readily available process of trigonometrical calculation.

The difference in modulation between the lights might be one of sequence in which each is flashed in turn. A set of logic instructions in the detector controller - would enable the detector to identify which light was being observed and thereby determine the distance, bearing and relative height of the lights with respect to the detector: In order that the orientation of the light array does not affect the measurement it may be necessary to have a spatial arrangement of the lights in three dimensions to avoid ambiguities in measurement.

In this manner a survey of an area can be carried out automatically by systematically moving either the light array or the detector system over the terrain to be mapped together with any other parameter detectors which provide the desired survey information.

Claims

1. A method of tracking and logging the varying position of a mobile object relative to an origin, by measuring the spatial angles of first and second lines of sight of prescribed radiation between the mobile object and a reference direction which is fixed relative to the origin, the first line of sight extending between a first radiation transmitter and a first radiation receiver, and the second line of sight also extending, but at an angle to the first line of sight, between a radiation transmitter and a radiation receIver, the transmitted radiation being modulated and the or each radiation receiver being tuned to said modulation so as to discriminate between background radiation and the prescribed radiation, the method including the steps of calculating the position of the obJect from a measurement oL the said angles, and recording the calculated positions in material form.

2. A method according to claim 1 wherein the first and second lines of sight share the sare radiation receiver, but have separate radiation transmitters spaced from eacn other.

3. A method according to claim 2 wherein the transmitters are on the mobile object.

4. A method according to claim 2 wherein the receiver is on the mobile object.

5. A method according to claim 1 wherein the first and second lines of sight share the same radiation transmitter, but have separate radiation receivers spaced from each other.

6. A method according to claim 5 wherein the transmittcr is on the mobile object.

7. A method of tracking and logging the varying position of a mobile object, substantially as hereinbefore described with reference to the accompanying drawing.