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FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to an airborne arrangement for the combined
display of a topographical moving map and navigational data.
Our invention is applicable to aerial-navigation systems, in which a
moving-map display shows the pilot of an aircraft a topographical map
which generally corresponds to the region being flown over. In this case,
the positioning of the map in the cartesian X and Y directions and the
rotational or angular orientation .theta. is controlled automatically as a
respective function of the longitude, latitude and heading of the
aircraft. The appropriate data (latitude, longitude, heading, etc.) are
supplied by the navigational system of the aircraft. The moving-map
display includes a computer which carries out servo-control operations in
the X, Y and .theta. directions on the basis of the navigational data.
In addition to displaying a topographical or other kind of map, the system
also produces an optically projected marker which generally indicates the
present position of the aircraft, or else the aircraft's intended
destination, or any other desired point on the map.
It is often useful to display other information for navigational purposes,
such as speed, fuel consumption, or the course to be followed. This
information is generally displayed by a cathode-ray trace employing random
scanning in order to form the symbols or alphanumeric characters to be
visualized.
According to a known technique, the image of the navigational data
displayed on the screen of a cathode-ray tube is mixed optically with that
of the movable map, the latter being produced by optical projection and
the mixing being performed by means of a semi-reflective mirror. The
assembly is arranged to project the two images at infinity and to perform
the function of an optical collimator whereby the pilot can look through
an optical pupil without the need for accommodation. In another known
system, the images are displayed on the screen of a cathode-ray tube, the
navigational data and the movable map being projected optically through
the rear of the tube. Systems of this nature necessitate the use of a very
special tube known as an optical-window tube.
In both of the above arrangements, the opto-mechanical assembly concerned
with the projection of the movable map must be situated at only a short
distance from the plane of display. Such equipment is heavy, bulky and
expensive and takes up a considerable amount of space on the instrument
panel, inasmuch as it is usually situated in a low-down viewing position.
OBJECT OF THE INVENTION
The general object of our present invention is to overcome such drawbacks
by providing a display arrangment which operates by alternating electronic
scans to combine the display of the map with that of the navigational
data.
SUMMARY OF THE INVENTION
In accordance with a feature of our invention, an airborne arrangment for
the combined display of a moving map and aerial-navigation data comprises
a television monitor for displaying a movable image of a map stored on a
film, servomechanical means for controlling the position of the image as a
function of the latitude, longitude and heading of the aircraft, a
generator assembly for producing video map signals corresponding to the
image to be displayed along with line and frame synchronizing signals
conforming to a line-by-line scan, and a symbol generator for producing
the navigational data in the form of synthetic video signals conforming to
a random scan. The monitor includes switching circuits operated by the
frame signal to change over between the video signals and the scan signals
and to allow the aerial-navigation data to be displayed, following each
display of the image of the map, during the frame blanking period.
BRIEF DESCRIPTION OF THE DRAWING
The above and other features of our invention will now be described in
detail with reference to the accompanying drawing in which:
FIG. 1 is a simplified diagram of a display arrangement according to the
invention;
FIG. 2 is a diagram of part of the arrangement of FIG. 1 showing ancillary
members forming a corresponding electronic navigational display system;
FIG. 3 is a more detailed view of a preferred embodiment of a video map
generator illustrated in block form in FIG. 1;
FIG. 4 is a table serving to explain the principle of subdividing a map to
form a film;
FIG. 5 is a view of part of a film showing the regions which are examined
with the generator shown in FIG. 3; and
FIG. 6 is a diagram of another embodiment of the video map generator of
FIG. 1.
SPECIFIC DESCRIPTION
The display arrangment generally illustrated in FIG.1 includes an assembly
1 for generating a composite map signal VCC. This signal is designed for a
line-by-line display of television type and consists of a video map signal
VC, a line synchronizing signal SL and a frame synchronizing signal ST. An
extractor circuit 2 enables the video signal and the synchronizing signals
to be separated. During the working period of the frame cycle, the video
signal VC is transmitted to an oscilloscope comprising a cathode-ray tube
3. A scan circuit 4 converts the synchronizing signals SL and ST into the
deflection signals DX and DY required for the line-by-line scan which is
to be produced. These deflection signals are applied to electrostatic or
electromagnetic deflecting members such as the coils indicated at 5.
During the flyback period of the frame cycle, symbols or alphanumeric
characters are displayed with the aid of a random scan. The appropriate
video signal for this presentation is generally termed synthetic video and
is designated VS in the FIGURE. The VS signal and the appropriate
delfection signals DX and DY for each trace to be produced are supplied by
a symbol generator 6. Two switching circuits 7 and 8, which are operated
periodically by the frame signal, and more specifically by the leading
edge of the frame blanking signal, enable the switching of the video and
beam-deflection channels, respectively.
It is understood that this diagram is a general one which allows the
functional structure to be shown at the expense of a certain amount of
simplification. In particular, the video map signal VC is applied to a
grid of the cathode-ray tube 3 after passing through reception circuits
which are not shown, and the video-symbol signal VS is applied in the form
of a brightening signal to the electron-emitting cathode. The
corresponding amplifying circuits are also not shown.
The volume of the generator 1 is considerable since it contains the map
stored on a positive film, feed means for transporting the film past
optical devices, and other components described below. FIG. 1 shows that
the generator 1 may advantageously be positioned remote from the tube 3
and thus away from the aircraft's instrument panel. The display
arrangement proper may consist of a conventional monitor or receiver which
incorporates the elements 2, 3, 4 and 5 supplemented by the switchover
means 7 and 8.
The circuitry indicated in broken lines consists of a generator 9 producing
video overlay signals VI which it is desired to show superimposed on the
video map signal VC. These superimposition or overlay signals are combined
with signal VC in a video mixing circuit 10. The signals VI produce a
predetermined amplitude change (increase or decrease) of signal VC so as
to cause one or more symbols of predetermined configuration to appear at
selected locations on the screen, these symbols representing for the
viewer information additional to that which is formed elsewhere by means
of the symbol generating circuit.
The arrangement as a whole is controlled from a block 11, which represents
a control unit and which includes in particular a display computer. In
FIG. 2 we have shown the computer at 15; element 16 represents a command
post on which the pilot's controls are grouped and element 17 represents a
memory of the read-only type. The latter is intended to indicate during
the flight which superimposed and symbol information is to be displayed
and at what times. This memory 17 is programmed, accordingly, before the
flight as dictated by the mission to be performed and may take the simple
form of a magnetic-tape cassette or a semiconductor store, for example. On
the basis of the flight program, the commands given by the pilot, and the
positional and orientation information received from the navigation system
(not shown), the display computer produces signals to control the
aforementioned generators 1, 6 and 9 so as to cause the combined display
required by the pilot to appear. Provision is also made for the map video
channel VCC to be switched out at a command from the pilot and to be
replaced by another video channel VR produced by an ancillary generator
18. The switching device, shown at 19, also has an off position. The video
signal VR may, for example, be supplied by an airborne radar system or an
infra-red camera.
FIG. 3 shows a preferred embodiment of the generator 1 producing the video
map signal.
In this embodiment a dot-by-dot optical examination is performed by using a
flying-spot scanning tube 25 provided with line-by-line scan circuits 26
and circuits 27 for generating the line and frame synchronizing signals SL
and ST. The light radiation from the spot produced is picked up by an
optical objective 28 and converted by the latter into a beam of parallel
rays for the purpose of optical separation by a semi-reflective mirror 29
inserted in the optical path. This mirror is treated in such a way that it
produces a second optical channel for monitoring the position of the scan,
this second channel carrying only a small fraction of the light energy
contained in the incident beam, for example a few percent. The remaining
major fraction forms the principle channel which is used for scanning the
map and in this instance is the channel reflected by the mirror. A second
optical objective 30 acts to focus the beam and recreates a point of light
representing the spot at the level of the image of the map to be analyzed.
The map is produced on a film 31 which is wound on spools 32 and 33. The
film is obtained by taking successive shots of parts of the mapped area to
be recorded, using a breakdown as shown in the diagram of FIG. 4. The
breakdown into m rows and n columns involves the production of mn images,
which are recorded photographically in the indicated order I.sub.1 to
I.sub.m and then I.sub.m+1 to I.sub.2m and so on, which amounts to placing
end-to-end the n successive vertical strips resulting from the breakdown.
Two image areas I.sub.j and I.sub.j+1 have been specifically illustrated
in FIG. 3.
The scanning tube 23 performs a line-by-line scan which on the film results
in a corresponding scan of a restricted zone Zj of the image I.sub.j
concerned (FIG. 5). The film also includes, in accordance with known
techniques, coded lateral tracks 34 to indicate the number of the image
currently being scanned and the position of scan.
Downstream of the film lies an opto-electrical detection device consisting
of an optical focusing objective 35 and a photodetector 36 which emits the
video map signal VC. This signal is combined with the synchronizing
signals SL and ST in a mixing circuit 37 to produce the signal VCC
intended for the display assembly, which may thus be remotely situated.
The position of the scan on the tube is difficult to establish with the
accuracy required to identify a reference point, generally the centerpoint
of the zone Zj, which is normally selected to indicate the present
position of the aircraft. We therefore prefer to check on the position of
the scan by means of the second optical channel whose beam is focused by
the objective 40 and impinges on a photodetector 41 which may be preceded
by a diaphragm 42. The position of the photodetector corresponds to that
of the reference point which in the present case is assumed to be situated
at the center of the screen of the tube. The cell 41 thus detects the
passing of the spot during each frame scan. The corresponding detected
signal is applied to a comparison circuit 43 which receives from the
synchronizing generator pulses whose position in time corresponds to the X
and Y co-ordinates of the reference point concerned. When the position of
the scan varies from one frame scan to the next, circuit 43 emits error
signals representing the longitudinal Y shift, i.e. the number of lines of
displacement, and the transverse X shift, i.e. the displacement along the
reference axis, which in the present case is the centerline. The
comparison circuit may for example consist of a counting circuit to enable
the periods of a high-frequency clock signal to be counted, in known
fashion, to give an accurate indication of the displacements.
Corresponding error signals are fed back to the scan circuit 26 to alter
the deflection signals accordingly and to keep the center of the scan
aligned with the center of the screen.
The cell 41 is set up beforehand so that its position coincides exactly
with the planned reference point.
In the event that a color film is to be scanned, the elements 35 and 36 are
supplemented by an optical chrominance discriminator to separate the
various color channels, there being as many photodetector cells as there
are color channels.
The position and the angular orientation of the scanned zone Zj relative to
the scanned map section I.sub.j ; are slaved to the movements of the
aircraft but can also be controlled by the pilot, as by manual shifts of
the map. An on-board computer 45 receives data on the position and
orientation of the aircraft from the display computer 15, representing the
latitude, longitude and heading to be shown. On the basis of these data,
the computer produces signals for controlling rotation .theta. and
position in directions X and Y. The servo-control of position in direction
Y comprises circuits 46 which feed a device 47 for driving the spools
carrying the film. Rotation of the spools shifts the film parallel to
direction Y in a sense corresponding to the sign of the positional error
and for a distance sufficient to cancel out the error. The servo-control
of position in direction X similarly comprises circuits 48 which feed a
driving device 49. The latter acts on the angular position or tilt of the
mirror 29 relative to the optical axis Z. The result is a transverse
movement of the zone Zj in such a direction and to such an extent as to
cancel out the error in the X position. The Y-position reference is
supplied from information carried by the tracks 34. This information is
read by making use of the scanning tube 25 during the frame blanking
periods to produce a second scan in the lateral area of the film where the
coded tracks are carried, these being shown in detail in FIG. 5. During
the frame blanking period, which is made sufficiently long, the scan
circuit 26 produces other deflection signals so that the spot of the tube
is moved off center and scans a lateral zone Zk. The coding of the tracks
is such as to identify the image number and the position. It consists of a
coarse coding for the image number and reference positions on one track,
and a precision coding for indicating position by means of a train of
pulses on another track. Zone Zk is preferably examined by scanning the
two coding tracks 34 in the Y direction as illustrated. The Y-position
signals which are detected in this way by the cell 36 are transmitted to
the computer 45 by means of a switching circuit 50, inserted in the output
of the detector 36, which is controlled by the frame signal ST.
The X-position reference is supplied by an angular-position sensor, which
may consist of a potentiometer 53 whose moving contact is shifted by the
driving device 49 in synchronism with the rotary movement of the mirror
29. The voltage measured between the moving contact and a reference
potential (ground) is representative of the angular position of member 29
and is applied to the on-board computer 45 to allow it to produce an error
signal, by making a comparison with the received data on the position of
the aircraft, which is applied to the servo-circuitry 48.
The objective 30 is designed to provide a sufficiently large field to cover
the possible movements of zone Zj in the image in direction X. A more
elaborate structure may be devised with an objective 30 of more restricted
field provided that its linear position in direction X is servo-controlled
in relation to the angular rotation of the mirror 29.
Another possibility is to hold the mirror 29 stationary and to move the
film and spools as a whole in direction X. The X position is then fed back
by means of a potentiometric sensor, for example, which is mounted on a
carriage carrying the film and spools.
The angular reorientation .theta. of the map is caused by rotating the
direction in which the spot sweeps across the screen, which results in an
identical rotation of the zone of the scanned film about the reference
point (FIG. 5). The servo-control of the position of this point ensures
that the center of rotation remains fixed in transposition.
The degree of rotation specified by the display computer 15 is transmitted
to the on-board computer 45, which controls the scan circuits 26 via a
connection 51 to produce the appropriate deflection signals.
This rotation can be canceled by action on the part of the pilot. An order
from the control station 16 is transmitted from the display computer 15 to
computer 45, which cancels out the rotation.
The map can be shown on different scales by increasing or decreasing the
dimensions of the zone Zj being scanned, this zone being spread over the
entire face of the screen of the display tube 3.
The order for enlargement is given by the pilot and is transmitted via the
control station 16 and the display computer 15 to the computer 45, which
in turn controls the scan circuits 26 via a connection 52, to produce the
appropriate deflection signals.
Provision may also be made for the displayed area to be off-centered so
that its midpoint does not coincide with reference point, the offset being
produced by video overlay using generator 9 and mixer 10 (FIG. 1).
The rotation, enlargement and off-centering of the scan are brought about
by modifying the deflection signals by well known techniques, and the
servo-control of the position of the reference point may similarly be
performed by conventional techniques.
FIG. 6 shows another embodiment of the component 1 (FIG. 1) generating the
video map signal. The zone Zj to be scanned is illuminated by means of a
light source 55 which is positioned at the focus of an objective 56. An
image of the zone is formed on the target of a television scanner tube or
pick-up tube of a camera 57. The output signal of camera 57 is fed to the
display tube or oscilloscope 3 of FIG. 1 via switches 7, 8. The light
source 55 may consist of light-emitting diodes. The film 31 is placed in
the focal plane of a second objective 58 which forms an image of this
plane at infinity. This image is picked up by an entry objective 59 which
precedes the scanner tube and which is focused on the target of the tube.
The optical path includes a semi-reflective mirror 60 and a reflective
mirror 61 deflecting the incident light rays onto the tube 57. The mirror
60 enables position-reference information produced by a second optical
channel formed by a light source 62, a diaphragm or mask 63 and an optical
objective 64 to be combined with the rays from the first optical channel
described above. The combination of elements 62 and 63 produces a point of
light or an illuminated reticle at the focus of the objective 64. This
point is superimposed on the image projected upon the target and forms the
visible reference point, which generally represents the position of the
aircraft. As described in the case of FIG. 3, the X and Y movements of the
film 31 are produced by rotating the mirror 60 and driving the spools. The
frame blanking period, utilized for the display of navigational data as
described above, is generated within tube 57 by the usual sweep Circuits
replacing the scanning unit 26 of FIG. 3 and generating the sync signals
SL, ST shown in FIG. 1.
The rotation of the map is brought about by an optical device, such as a
so-called Pechan prism 65, which is rotated about the optical axis Z by a
driving device 66 which may be controlled from the on-board computer (45,
FIG. 3). The scanner tube may be of the vidicon type or may be a
semiconductor matrix forming a charge-coupled device. The objective 59 may
be of variable focal length to produce a desired enlargement.
In the case of a source 55 formed by light-emitting diodes, the diodes may
emit in separate spectral bands corresponding to different colors. In
conjunction with a color film it is possible, by selecting the diodes, to
show only the parts of the map appearing in certain chosen and selectively
allotted colors, with for example roads in yellow, waterways in blue, etc.
It will be understood that many modifications may be made without exceeding
the scope of the invention, which is particularly distinguished by the
combined presentation of a topographic moving map and aerial-navigation
data on the screen of a cathode-ray tube or equivalent equipment, the
image of the map being converted into a video signal.
By way of example, the prism-equipped rotating system 65, 66 of the
embodiment shown in FIG. 6 may be introduced into the embodiment of FIG. 3
in which a scanning tube 25 is used in lieu of pick-up tube 57.
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