A remotely controllable position indicator system

A remotely controllable position indicator system arranged to determine the relative position of two bodies and their relative orientation. A movable remote control device is controllable to transmit command radiation signals. A fixed reference station executes commands represented by the command radiation signals. The remote control device has a transmitter while the reference station has a receiver or receivers which monitors the intensity of the radiation received and distinguishes the source of the radiation. A computer is programmed to determine the direction of the reference station from the remote control device using a comparison of monitored intensity of radiation received from the transmitter to give the direction of the receiver from the directional transmitter. One or more of the transmitters is controllable to transmit command signals and the receiver is arranged to receive the command signal. A switch for the transmitter or transmitters initiates radiation command signals to enable an operator to selectively point at a target and then issue a command radiation signal for execution by the reference station.

This invention relates to locating systems for use in a wide variety of 
applications. 
Many applications are primarily directed to the domestic market and 
particularly for use with video games where interaction is required 
between targets on a screen and a toy gun or other toy weapon, and 
possibly the relative location of players of the games and the screen 
during the playing of the game. Other main interest arises where a user of 
a video screen wishes to interact with images on the screen to respond to 
interrogation by or to control those images, for example to select items 
on a menu displayed on the screen by remotely pointing towards chosen 
regions of the screen. In this context a shopping list could be compiled, 
that is programmed into a machine, by selectively pointing to items in 
turn which appear amongst a displayed list of available items. 
In specific applications of interest it is necessary for a remotely hand 
held implement (toy gun, etc.,) or for a remotely situated body to be able 
to determine the relative position of the implement or body. The fixing of 
the relative location also enables decisions to be made at the remote 
position to alter that position as may be required or if relayed to the 
target or screen for the target or screen to respond accordingly, for 
example, when the gun is pointing at a target on the screen. 
According to the invention there is provided a locating system for a body 
in which the body is movable relative to a fixed reference station, the 
system including two transmitter and receiver pairs in which the 
transmitters form one directional transmitter and are situated at the body 
and the receivers form one directional receiver and are situated at the 
reference station, means for monitoring the intensity of radiation 
received by each receiver and means for synchronising the radiation of 
each transmitter with the monitoring of the intensity, and computer means 
programmed to determine the direction of the body from the reference 
station (angle B) and the direction of the reference station from the body 
(angle A), using a comparison of radiation received between each receiver 
of the directional receiver from a single transmitter to give the 
direction of the transmitters from the directional receiver and using a 
comparison of radiation received by one receiver of the directional 
receiver from two transmitters of the directional transmitter to give the 
direction of the receivers from the directional transmitter, in which one 
or more of the transmitters is controllable to transmit radiation command 
signals and the receivers are arranged to receive the command signals, 
including switching means for the transmitter or transmitters to initiate 
radiation command signals to enable an operator to selectively point at a 
target and then issue a command radiation signal for execution by the 
reference station. 
The locating system may include three or more transmitters at the body and 
three or more receivers at the reference station forming two or more 
different directional transmitters and two or more different directional 
receivers respectively arranged to form a number of transmitter and 
receiver pairs for two or more planes in which the computer means is 
programmed to determine the direction of the body from the reference 
station and the direction of the reference station from the body in three 
dimensions. 
The computer may be programmed to determine the distance of the body from 
the reference station using a summation of the radiation received from the 
transmitters. 
The radiation may be pulsed infrared radiation. 
The transmitter may be arranged to transmit in four directions positioned 
equally around a central pointing axis of the body each at approximately 
15.degree. to the central axis and the receivers comprise four directional 
elements positioned equally around a central axis with each element 
positioned at approximately 15.degree. to a central receiving axis. 
In many applications knowledge or calculation of the actual relative 
positions will be required but in some applications only an approximate 
determination is sufficient or only the position in respect of one plane 
need be determined. Thus for example, embodiments may be arranged to be 
sensitive to measure locations only in respect to the one plane and/or 
determine only a relative direction of an object and not its distance from 
a target, screen or the like. 
Embodiments of the invention make use of courses of radiation and sensing 
radiation emitted at different places and as such the radiation can take 
virtually any form including electromagnetic radiation and sound. 
According to which form of radiation is chosen, but as will be well 
understood by those skilled in the art, certain specific characteristics 
associated with the chosen form of radiation will affect calibration of 
equipment, natural dispersment patterns of that form of radiation and so 
on. For various reasons including the present relative cost of available 
component devices, relative ease of processing the information especially 
as ambient variations are then easily discounted, in embodiments of the 
invention pulsed infrared radiation is generally preferred. 
The above systems enable relative angles or relative directions from 
imaginery lines connecting the source and the body to be determined. For 
many applications such information is sufficient, for example whether a 
toy gun, or body, is pointing towards the target can be determined simply 
by determining the relative angle or direction of the body in relation to 
the source, which is adjacent the target. If the actual location is 
required to be determined, that is the distance of the body from the 
source, then the intensity of radiation received by one of the detectors 
or the mean intensity of the two or three detectors may be used. Radiation 
intensity falls off with distance so that the actual intensity received is 
used as a measure of distance. In most embodiments this is normally and 
more easily achieved by periodic calibration of the system. 
In the embodiments where both orientation and direction are determined, the 
system can be used for fitting one part to another, say for an airborne 
refuelling application. Both the so-called "body", say the fuel line, and 
a support for the source, say the airborne tanker outlet hose, can be 
manipulated so as to mate, control means which responds to the relative 
orientation and position signals being arranged to move the fuel line into 
position. If a similar system is used on the outlet hose of the tanker, 
that is detectors are also mounted on the hose and a radiation source is 
mounted on the fuel line, the outlet hose can also be controlled to move 
into a suitable mating position. The attraction of such a duel system is 
that any discrepencies in the operations of the two systems will tend to 
cancel out and make the mating more efficient. It will be noted that no 
communication channels as such are necessarily required between the two 
parties, each party can make its own controlled adjustment. Thus, failure 
in communication channels between the tanker and the plane being fuelled 
cannot affect the successful mating.

In FIG. 1 a locating system 1 comprises a first body 2 and a second body 3 
which are in the same plane directly opposite to each other with the 
second body 3 pointing in a direction towards the first body 2 at an angle 
A. The first body 2 is provided with a directional radiation detector 4 
comprising two infrared photodetectors 5, 6 spaced by a fixed distance L. 
The second body 3 is provided with a first radiation source which is an 
infrared LED 7 having a wide field of radiation represented by the line 8 
showing the relative intensity of the radiation of the LED with angle, and 
a second radiation source which is another infrared LED 9 having a narrow 
field of radiation represented by the line 11. 
In FIG. 2 the second body 3 is in another position such that a line through 
the centres of the bodies subtends an angle B to the transverse axis of 
the first body 2. 
In FIG. 3 the field of radiation of the two LEDs is shown on a polar 
diagram to illustrate the relative intensities of light received at the 
photodetectors 5, 6. 
In use light from the first LED 7 is detected by the directional detector 4 
to determine the angle B. For example, in FIG. 1 where the angle B is zero 
since the second body 3 is directly opposite the first body 2, an equal 
intensity of light is received at the two photodetectors 5, 6. In FIG. 2 a 
greater intensity of light will be detected at photodetector 6 than at the 
photodetector 5 so that the angle B can be calculated from the relative 
light intensities at each photodetector 5, 6 with a knowledge of the fixed 
separation L and a knowledge of the shape and fall-off characteristic of 
the field of radiation 8 of the first LED 7. Light is then detected from 
the second LED 9 by the directional detector 4. Knowing the position of 
the second body 3 due to angle B, and knowing the shape and fall-off 
characteristic of the field of radiation 11 of the second LED 9 the angle 
A can be calculated. 
The calcuation to determine A and B depends upon the different radiation 
characteristics of the light being emitted by the LED 9 to that of LED 7. 
Because the light of LED 9 is confined or focussed the intensity of 
radiation is more concentrated along its central axis than the radiation 
of the LED 7. The intensity of light measured at the directional detector 
4 from the LED 7 is therefore relatively independent of the angle A. 
Referring to the polar diagram shown in FIG. 3 it can be seen that 
approximately equal amounts of light are received from the LED 7 at the 
photodetectors 5, 6 indicating that B is equal to zero, whereas the 
intensity of light from the LED 9 measured at the photodetector 5 is 0.96 
compared to 0.4 at the photodetector 6, allowing the angle A, here equal 
to 25 degrees, to be calculated. 
In FIG. 4 a first body 30 has first directional detectors 31 and a detector 
32. A second body 33 has a first LED 34 having a wide field of radiation 
36 and a second directional radiation source 37 comprising two separate 
LEDs 38, 39 both having narrow fields of radiation 38A, 39A, with one LED 
mounted on each of the two front faces of a block 40. The block 40 is 
shown in more detail in FIG. 4A, in which the two LEDs 38, 39 are mounted 
on two opposed sloping faces at approximately 5 degrees to the line 
transverse to the long longitudinal axis of the block 40. This makes the 
two fields of radiation 38A, 39A point in different directions separated 
by a mean angle of 10 degrees as shown in FIG. 4. 
The angle B is determined by measuring the light from the first LED 34 
using the directional detector 31 as hereinbefore described. The direction 
in which the second body 33 is pointing is determined by angle A measured 
by the intensity of light at the detector 32 from each of the two LEDs 38, 
39 on the directional source 37. 
In an alternative arrangement of the locating system of FIG. 4 the two LEDs 
38, 39 have a very wide field of radiation acting as point sources. The 
angle of the faces on the block 40 are arranged so that the fields of 
radiation 38A, 39A overlap in such a manner that the average intensity 
from the two LEDs 38, 39 is independent of the angle A. The LED 34 is 
therefore not required, since the angle B can be determined by the 
difference in the combined intensities from 38, 39 as they are pulsed at 
the same time. The LEDs 38 and 39 are then pulsed in succession to 
determine angle A as before. 
In many applications it is sufficient simply to calculate the angle A 
assuming the angle B is zero, or to calculate the angle B assuming the 
angle A is zero. In either case this could be carried out using the source 
37 in conjunction with the detector 32, without the requirement for the 
LED 34 and the detector 31. 
In FIG. 5 a first body 41 has a first directional detector 42 and a first 
LED 43 having a narrow field of radiation 44 and a second body 45 has a 
second directional detector 46 and a second LED 47 having a narrow field 
of radiation 48. In this embodiment each directional detector 42, 46 
comprises a two segment photodetector 49 with a focusing lens 50 in front 
of the detector 49 so that the segments respond to different fields of 
vision. 
Light from the first LED 43 is received at the second directional detector 
46 to give the angle B approximately and light from the second LED 47 is 
received at the first directional detector 42 to give the angle A 
approximately. Information relating to the angle B is then transmitted to 
the first body 41, using the LED 47 as the transmitter and the detector 49 
as the receiver. 
In FIG. 6 both a first body 51 and a second body 52 have a photodetector 53 
and a directional radiation source 54. Each directional radiation source 
54 is as described with respect to FIG. 4. Light from the source 54 on the 
first body 51 is detected at the second body 52 by the detector 53 to give 
the angle B approximately. Light from the source 54 on the second body 52 
is then detected at the first body 51 by the detector 53 to give the angle 
A approximately. Information relating to the angle B is then transmitted 
to the first body 51, using the source 54 as the transmitter and the 
detector 53 as the receiver. 
In FIG. 7 a first body 60 has a directional detector 61 comprising two 
ultrasonic receivers 62, 63 and a second body 64 has a source of radiation 
provided by an ultrasonic transmitter 65 having a narrow field of 
radiation 66. In order to determine the angle B the phase of the 
ultrasonic radiation is measured between the two detectors 62, 63. For 
example, where B is equal to zero the phase difference is zero since the 
radiation takes the same time to propagate to both detectors 62, 63. The 
phase difference is independent of the angle A. The angle A is determined 
by the difference in the intensities measured at the two detectors 62, 63 
and the range between the two bodies 60 and 64 is calculated by the 
absolute intensity measured at the detector 61. 
In FIG. 8 a video game is shown in which a first body in the form of a gun 
70 having a trigger 71 is used to aim at and "shoot" targets, generated by 
a computer (not shown), on a second body in the form of a television 
screen 72. Attached to the gun 70 is a ultrasonic source of radiation 73 
having a narrow field of radiation as described with reference to FIG. 7. 
Equally spaced about the periphery of the television screen 72 are four 
ultrasonic receivers 74. The orientation and position of the gun 70 with 
respect to the centre of the television screen 72 are calculated as 
described with respect to FIG. 7. The distance of the gun 70 from the 
screen 72 can be calculated from the absolute intensity of radiation 
received from the transmitter 65. Knowing the angles A and B and the 
distance it is possible to calculate where the gun 70 is pointing on the 
screen 72. 
The carrier frequency of the transmitter is 40K Hz modulated at a frequency 
of 500 Hz to produce a pulse train of sound waves. This enables the 
orientation given by angle B in FIG. 7 to be determined to an adequate 
accuracy for use with a 50 cm screen 72 with the gun 70 held typically up 
to 3 meters away from the screen 72. When the trigger 71 is pulled the 
modulation frequency changes to 550 Hz, which enables the computer to 
determine when the trigger is pulled and hence to indicate on the screen 
whether a target is "hit". 
By calculating where the gun 70 is in relation to the centre of the screen 
72 it is possible for the computer to take defensive steps to protect the 
targets. For example, the gun 70 could be used with a screen 72 where a 
target is hidden behind a movable obstruction. If the computer has 
determined where the gun 70 is, it can move the obstruction appropriately 
to defend the target. 
In FIG. 9 a gun 70 is used in conjunction with a television screen 72 as 
hereinbefore described with reference to FIG. 8. The gun 70 has a 
directional source 75 comprising 3 LEDs 76 mounted in the matter of the 
LEDs 38, 39 in FIG. 4A, pointing in three different directions towards the 
screen 72, to generate information in two plates. A directional detector 
77 having a three segment detector 78 and a lens 79 is mounted on the 
television screen 72. 
To determine the angle B the relative intensities of light from the LEDs 76 
is measured on the three detectors 78. To determine the angle A the LEDs 
76 are multiplexed in time together with a blank interval of time for 
synchronisation, to determine the intensity from each LED 76 in turn. When 
the trigger 71 is pulled the pulse frequency changes. 
Where it is necessary to distinguish the information sent from more than 
one source of radiation, time division multiplexing may be used as 
hereinbefore described. Alternatively the different sources may be pulsed 
at different frequencies or the different sources may be arranged to 
transmit at different wavelengths of radiation. Furthermore it is possible 
to use polarized light to distinguish between two sources of radiation. 
In the aforementioned arrangements it has been shown that it is possible to 
determine the direction of the second body from the first body angle B and 
the direction of the first body from the first body Angle A. It is noted 
that angles A and B depend on the arrangement of the directional detectors 
or directional dispositions of the bodies so that the relative orientation 
of the bodies is determined by angles A and B. 
Turning now to FIGS. 10 to 12, by way of background, in conventional 
display systems a joystick or mouse is often used to move a cursor about 
on a visual display unit. This allows, for example, graphics, menu 
selection and video games to be used in conjunction with the display 
system. A remote controller can be provided which allows considerably more 
freedom of action than a joystick or mouse for example. 
Referring to FIG. 10, the remote controller arrangement comprises an 
infrared light emitting diode 80 mounted on a visual display unit 81, a 
lens 82 fixed inside at the front of a pointing device 83 and an optical 
directional detector 84, also mounted inside the pointing device 83. The 
pointing device 83 is in the form of a toy-gun and has sights 85 and a 
trigger 86. The diode 80 is positioned in the middle of the top of the 
visual display unit 81. 
The remote controller is arranged so that when the pointing device 83 is 
aimed at the centre of the visual display unit 81, radiation from the 
diode 80 impinges on the centre of the detector 84. The axis of the lens 
82 is offset from the axis of the pointing device 83 to compensate for the 
diode 80 not being at the centre of the screen of the visual display unit 
81. 
Means for transmitting return signals to the visual display unit 81 are 
provided by a second infrared light emitting diode 87 located on the 
pointing device 83, and a second optical directional detector 88 located 
on the visual display unit 81 adjacent the diode 80. A second lens 89 is 
mounted in front of the second detector 88. The axis of the second lens 89 
is offset from the axis of the second detector 88 so that when the 
pointing device 83 is pointing at the centre of the screen, radiation from 
the second diode 87 impinges on the centre of the second detector 88. 
FIG. 11 shows the four segments of a quadrant photodetector 83 or 88, 
labelled A, B, C and D. An image 90 of the radiation from a diode 80 or 87 
is shown to be impinging on the centre of the detector 83 or 88. 
Referring to FIG. 12 there is shown a geometric representation of a remote 
controller, in which the pointing device 83 is positioned perpendicularly 
to the centre of the visual display unit 81. The lens 82 is at a distance 
z from the centre of the visual display unit 81. The gun 83 is pointing at 
a position X.sub.1, Y.sub.1, on the screen of the visual display unit 81 
with respect of the centre 0, 0 of the visual display unit 81. The centre 
of the image 90 of the radiation from the diode 80 impinges on the 
detector 84 at a position X.sub.2, Y.sub.2 with respect to the centre 0, 0 
of the detector 84. The detector 84 is located at a distance L from the 
lens 82. 
By similar triangles the relationship between the location X.sub.1, Y.sub.1 
on the visual display unit 8 and the location X.sub.2, Y.sub.2 on the 
detector 84 is X.sub.1 =Zx.sub.2 /L, Y.sub.1 =ZY.sub.2 /L. 
These relations are only true if the gun 83 is directly in front of the 
centre of the visual display unit 81. If the gun si at any other position 
in front of the visual display unit 81 the calculation of the position 
X.sub.1, Y.sub.1, on the visual display unit 81 must be compensated for by 
calculating the position of the gun 83 with respect to the centre of the 
visual display unit 81. This is achieved using the second diode 87 and the 
second detector 88, using the same reasoning given above, to give a 
location for the gun 83 of z, X.sub.3, Y.sub.3 with respect to the centre 
0, 0, 0 of the visual display unit 81. 
The operation of the remote controller is now described, in which the gun 
83 is used with a video game displayed on a TV minitor 81. 
The distance z is related to the total intensity of radiation from the 
second diode 87, detected by the second detector 88. In practice the gun 
83 is held initially a known distance from the TV monitor to allow the 
system to be calibrated. The diode 80 is adapted to give a viewing angle 
of almost 180.degree., so that the pointing device may be used at a large 
angle from a central axis of the TV monitor 81. The second diode 87 has a 
viewing angle of approximately 30.degree. to conserve optical power, and 
the gun 83 is used at a typical distance of 2 meters from the TV monitor 
81. 
The location X.sub.2 is related to the intensity of radiation impinging on 
the segments A, C divided by the total intensity of radiation impinging on 
all four of the segments. 
The location Y.sub.2 is related to the intensity of radiation impinging on 
the segments A, B divided by the total intensity of radiation. 
In order to transmit return signals to the normal control system of the TV 
monitor 81, the diode 80 is pulsed in phase with the faster 
synchronisation pulses for the line and field scan on the TV monitor 81. 
The pulses are detected by the detector 84 and reproduced at the gun 83 
and phase shifted in accordance with the information from the detector 84, 
related to the location X.sub.2, Y.sub.2. The second diode 87 is then 
pulsed with this information, together with a signal from the trigger 86. 
The second detector 88 receives the information which is then used to 
calculate the location X.sub.1, Y.sub.1 on the visual display unit 8 
according to the equations X.sub.1 =Zx.sub.2 /L and Y.sub.1 =ZY.sub.2 /L, 
taking into account the position Z, X.sub.3, Y.sub.3 of the gun 83. If the 
location corresponds to a target on the visual display unit 81 and if a 
signal is coterminously received from the trigger 86, then the target is 
`hit`. 
Alternative methods of providing the return signals could be used. For 
example, the gun 83 could be wire connected to the TV monitor 8 to allow 
electrical transmission of the return signals. Alternatively a 
retro-reflective mirror arrangement could be mounted on the gun 83, 
together with an optical modulator to modulate the optical return signals 
to the control system of the TV monitor 81, in accordance with the 
location X.sub.2, Y.sub.2. The modular could be a chopper. The mirror 
could also be mounted at an angle on a rotating disc. 
It should be appreciated that for the remote controller to operate 
correctly the X-axis of the pointing device and the X-axis of the visual 
display unit should be kept at least approximately parallel. 
FIGS. 13 to 17 show a locating system for use for a video game or to move a 
cursor across a television screen. The system comprises a gun 100 having a 
trigger 101 for use with a television screen 102. The gun has a 
directional transmitter 103 comprising four infra-red LEDs, of the type 
V394P III made by AEG-Telefunken, which are not focused. The four LEDs 
include a left pointing LED 106 a right pointing LED 107, an upward 
pointing LED 108 and a downward pointing LED 109 (see FIG. 14) in the 
direction towards the television screen 102. The LEDs are mounted on the 
faces of a square based pyramid having sloping faces at an angle of 
approximately 15.degree. to the base of the pyramid. The gun is battery 
powered having a mercury switch inside which switches the gun on when the 
gun is held upright. 
A directional receiver 111 is positioned on top of the television screen 
102 and comprises four infra-red detectors having wide receiving angles. 
The directional receiver 111 includes a left pointing detector 112, a 
right pointing detector 113, an upward pointing detector 114, and a 
downward pointing detector 116, in a direction towards the gun. The 
detectors are mounted on the inside faces of an open square based pyramid 
having sloping faces at an angle of approximately 15.degree. to the open 
base. 
FIG. 14 shows the circuit details inside the gun 100, and FIG. 15 shows the 
waveforms generated. 
An oscillator 117, running at 25 kHz is used to clock a pulse sequence 
generator 118 to provide signals B, C, D and E which are used to control 
the output of the four LEDs 106, 107, 108 and 109 respectively through a 
power driver 119. 
A three-pole switch 121 is connected to the trigger 101. It has an off 
position 122 and two controlling positions 123, 124. 
Referring to FIG. 15 the LEDs are pulsed in turn over a period of four 
cycles of the oscillator. When the trigger 101 is in the first controlling 
position 123, a pulse is generated to drive all four LEDs at the same time 
on a sixth cycle. When the trigger 101 is in the second controlling 
position 124 a pulse is generated to drive all four LEDs on a seventh 
cycle. After the eighth cycle the sequence is repeated. 
The waveforms H and J show the signals that are received at the left 
pointing detector 112 and the right pointing detector 113 respectively. 
The aim of the gun 100 relative to the receiver, which gives the 
previously referred to angle A see for example FIG. 1 is determined from 
the relative strengths of the signals received from pairs of LEDs by any 
one of the detectors. In this example the gun 100 is aimed downwards and 
to the left of the centre of the television screen 102. The signal 
received at each of the detectors from the left pointing LED 106 is 
therefore greater than the signal received from the right pointing LED 107 
and the signal received from the upward pointing LED 108 is less than that 
from the downward pointing LED 109. 
The position of the gun 100, that is the direction of the gun from the 
receiver 111, which gives the previously referred to angle B, is 
determined from the relative strengths of the signals received from one of 
the LEDs between pairs of the detectors. 
FIG. 16 shows the circuitry that is used at the directional detector 111. 
The signal received at each detector is first amplified in the 
pre-amplifiers 130. The amplified signals are then fed into individual 
filters 131, rectifiers 132 and integrating circuits 133 and at the same 
time each of the amplified signals are fed into a mixer circuit 134. The 
output of each of the integrating circuits 133 from each of the detectors 
is used to determine the position of the gun 100 relative to the 
television screen 102. 
The mixer 134 combines the signals from each detector and then the output 
of the mixer 134 is divided into a pulse amplifier 136 and a zero crossing 
detector 137. The output of the pulse amplifier 136 is used to determine 
the aim of the gun 100. By combining the signals using the mixer 134 the 
descrimination of the detector is improved. The error due to the fact that 
a single detector at the centre of the pyramid is not used is also 
reduced. The output of the zero crossing detector 137 which has the 
waveform k is used to feed two monostables 138 and 139 which are used to 
synchronize the detector, with the pulses from the four LEDs. 
FIG. 17 shows a circuit in the receiver to amplify the detector signal. 
FIG. 18 shows the receiver waveforms of the synchronisation. 
A computer is used to receive the signals from the detector circuit and 
process them to control the television screen 102. The fact that the 
directional detector is not mounted at the centre of the television screen 
102 is taken into account in the processing software of the computer. 
The distance of the gun 100 from the screen 102 is calculated from the 
combined intensity received by the receiver 111 from all of the LEDs. The 
calculations of the range and angles A and B are then used to compute 
where on the screen 102 the gun is pointing, as described with reference 
to FIG. 12. The greater the distance of the gun from the screen the more 
the point position moves over the screen for each unit of angular change 
of aim. 
It is important to note that the gun 100 can be placed almost anywhere in 
front of the screen 102 and its direction and aim relative to the screen 
102 can be determined. The output of the detector is analogue so that 
pointing position can be anywhere on the screen 102. 
In another embodiment it would be possible to use laser LEDs instead of 
ordinary LEDs to increase the range of the locating system. 
The locating system enables the possibility of the use of, for example, a 
toy-gun with an information display, displaying a video game in three 
dimensions, because information as to the position of the toy-gun is known 
by the control of the information display. This information could be used, 
for example, to put up defences for a target against the toy-gun. 
Further examples of uses for the remote controller of the present invention 
include, an interface for handicapped people with a display system to 
create drawings or music. The remote controller could be used by an 
operator, such as a lecturer, at a distance from an information display. 
The signal from the pointing device could have two levels, for example, to 
select the cursor and to execute a command from a menu. A well engineered 
version of the remote controller could be used for target practice and 
training to replace a conventional firing range. 
In the specification the terms "directional transmitters" and "directional 
receivers" are used. A directional transmitter is capable of transmitting 
in two or more directions and for three dimensional location at least 
three directions are required in at least two planes. At least the 
approximate location of the transmitting elements, that is the sources of 
transmission must be known and also the mean plane between diverging 
transmissions or separated elements relative to the movable body or fixed 
body (or reference station) must be known. The mean planes of response of 
each pair of detector elements of the directional receiver must be known 
relative to the movable body or the fixed body with whichever the receiver 
is associated. 
It will be noted that where the aim of a gun or direction of movement of an 
object relative to a third or fourth object is to be determined or 
controlled, it is only necessary to know the relative position of the 
third or other object relative to a reference station (say, the first of 
the two objects in the early description). The gun (or second object) can 
then be located and/or directed with reference to the reference station to 
aim at or travel towards the third or fourth objects.