Cartographic indicator system

An indicator system satisfies multiple flight-mission requirements by providing an aircraft pilot with a visual display consisting of a movable map and navigational data. The map is stored in video form in a high-capacity compact mass memory consisting of a video disk. The system further comprises a symbol and character generator as well as an intermediate memory which has a capacity larger than required for the map-zone image to be displayed together with navigation symbols on a television monitor. The unit is controlled by a microprocessor on the basis of data relating to latitude, longitude and heading of the aircraft in order to refresh the intermediate memory and to obtain an image displayed with a "top-north" or "top-heading" orientation.

This invention relates to a cartographic indicator system for the combined 
visualization of a movable map and of navigational data. 
The invention is more particularly applicable to the construction of an 
electronic air-navigation indicator system. A cartographic indicator is 
primarily intended to provide an aircraft pilot with a geographical map of 
the land area over which his aircraft is flying. The map is intended to 
move continuously in relation to the flight of the aircraft and its 
position is controlled automatically in the two directions of cartesian 
axes X and Y as a function respectively of the longitude and latitude of 
the aircraft. Furthermore, the course of the aircraft can be taken into 
account in order to control the position of the map in rotation .theta.. 
Data relating to latitude, longitude and course are supplied by the 
navigation system of the aircraft (sensors, inertial navigation unit and 
so on). The cartographic indicator comprises computing means (airborne 
computer, specialized computing circuits and so on) which utilize 
navigational data in order to control servo systems for positioning the 
map visualized at X, Y and .theta.. 
In addition to visualization of a geographical map or the like, the 
indicator system produces a reference mark or representative point 
indicating the position of the aircraft or alternatively of a target to be 
hit or any other particular point. 
It has proved useful in practice to visualize other items of information 
relating to navigation such as speed, fuel consumption, course to be 
followed and so forth. Such items of information are fairly frequently 
produced by CRT (cathode-ray tube) display, the line being plotted in 
accordance with the so-called random-scanning mode so as to form the 
symbols (vectors, circles and so on) or the alphanumeric characters to be 
displayed. 
It is a common practice to produce navigational and other information such 
as tactical data combined with the information provided by the 
geographical map of the region traversed by the aircraft and displayed on 
a single CRT (cathode-ray tube). In accordance with a corresponding 
technique which is already known and described in particular in U.S. Pat. 
No. 3,507,993, the map information is pre-recorded as a function of the 
course to be followed and stored in video form on a magnetic tape in the 
case of the geographical areas to be traversed during a particular mission 
under consideration. The video tap is placed on board the aircraft in a 
readout device which is synchronized with the forward travel of the 
aircraft with respect to the ground in such a manner that both the 
tactical and navigational information combined with the map information 
are produced in superimposition on the screen of the cathode-ray tube. 
Reference is also made to commonly owned U.S. Pat. No. 4,138,726. 
This design solution is subject to disadvantages arising from the fact that 
the recording remains fairly substantially limited to flight over land 
areas corresponding to the mission. Since a different route corresponds to 
each new mission, a fresh recording must therefore be performed. Recording 
of a geographical map covering a very large area and corresponding to a 
plurality of routes and missions cannot be contemplated, mainly on account 
of the excessive access times and the greater complexity of coding. 
One aim of the present invention is to overcome these limitations by 
employing in particular a high-capacity fast-access mass-memory unit of 
the video disk type which makes it possible to record a map of a very 
large area and permits high flexibility of operation. 
In accordance with a distinctive feature of the present invention, there is 
provided a cartographic indicator of the type comprising means for storage 
and reading of the map which is recorded in the form of a video signal 
adapted to the visual display envisaged and of coded position signals, 
means for generating symbols and especially an aircraft position signal, 
and means for combined visual display of the map video and of the symbols. 
Computation and management means are also provided for controlling as a 
function of the aircraft position, on the one hand the reading of the 
stored map and the selection of the video corresponding to the ground area 
being traversed by the aircraft and, on the other hand, the symbol 
generator for extraction of the desired symbols. In accordance with the 
invention, storage and reading means are designed in the form of a video 
disk device in which the map is recorded zone by zone while subdividing 
the map into two sets of adjacent bands parallel to a first reference 
direction Y. Said sets of bands are relatively displaced in the second 
reference direction X at right angles to the first so that the respective 
bands overlap in the direction of relative displacement. The coded 
position signals correspond to the latitude and to the longitude of each 
zone and the map video signal is transmitted to the display unit via an 
intermediate memory or storage device having a capacity which is larger 
than that of the image to be displayed.

In the general diagram of FIG. 1, the cartographic indicator system 
comprises in combination: means 1 for storage and reading of the map 
recorded in the form of a video signal adapted to the display envisaged 
such as, for example, a television image resulting from a line-by-line 
scan of the screen of a monitor; symbol-generating means 2 for producing 
in particular a reference mark representing the aircraft position in the 
display image; means for combined display of the map video and of the 
symbols represented by a display device 3 such as a television monitor, 
and a mixing circuit 4 or the like for combining the map video and the 
symbol video to be displayed; means for computation and management of the 
complete assembly in order to control on the one hand the device for map 
reading at 1 and selecting the map video corresponding to the overflight 
zone or ground area traversed by the aircraft and, on the other hand, the 
symbol generator for extraction of the desired symbols as the flight 
proceeds: these means are designated schematically by a block 5 which can 
essentially consist of a microprocessor which receives the 
aircraft-position data SX, SY and S.theta. from ancillary instruments 6 
installed on board and forming part of the navigation system. The signals 
SX and SY correspond to the latitude and to the longitude and the signal 
S.theta. corresponds to the course of the aircraft. 
In accordance with the invention, the memory device shown at 1 and employed 
for storing the map is designed in the form of a video disk 7 which is 
read according to requirements. The block 1 represents a video disk device 
with its means for reading and driving of the video disk. 
In accordance with another particular feature of the invention, the map 
signal extracted by controlled readout of the disk is not transmitted 
directly to the display device 3. An intermediate memory device 8 is 
interposed in this link. Said intermediate memory has a higher capacity 
than that of the image to be displayed on the screen at 3 as well as 
providing random access to writing and providing sequential readout at the 
same frequency as the display. The management unit 5 produces 
corresponding command signals for reading and writing control of the 
memory 8 as a function of the data X, Y and .theta.. As will become 
apparent hereinafter, introduction of the memory 8 in the combination 
makes it possible to limit the video-disk readout since only the 
memory-refreshment video signals are to be extracted as a function of the 
flight evolution of the aircraft. This memory introduction also makes it 
possible to solve the problem of continuity of display and to take into 
account the course parameter .theta.. 
The combination is completed by a circuit 9 for analog-to-digital 
conversion and coding of the information extracted from the video disk for 
subsequent writing of said information in the intermediate memory 8. 
Similarly, a circuit 10 for decoding and digital-to-analog conversion is 
provided for processing the data extracted from the intermediate memory 8 
in order to display the map on the indicator 3. The connections between 
the blocks 5 and 8 represent in schematic form the read/write controls of 
the intermediate memory 8. 
The cartographic indicator system makes use of the mass-memory unit 1 of 
the video-disk type which is read according to requirements by means of a 
suitable control signal generated by the management and computation 
circuits 5 as a function of the aircraft position parameters. The 
advantage thus secured is undeniable since the number of images stored on 
a video disk 7 is very large and can amount to 50,000 images, thus 
endowing the memory unit 1 with a very high density. By way of example, in 
order to display on the screen of the indicator 3 images 13.times.18 cm in 
size of a map having a scale of 1/25000, the video disk is capable of 
storing a total map covering a ground area of approximately 
8500.times.8500 km. In one non-limitative embodiment, the disk 7 which is 
usually of plastic material permits recording of the map which is 
accordingly written thereon in the form of grooves forming a spiral. The 
disk is driven in rotation at a speed of 25 revolutions per second, for 
example; one revolution corresponds to the recording of one video image. 
Writing of the video signal is performed in a succession of micro-cups of 
variable length and spacing along each turn, thus constituting a groove. 
The pitch of the spiral is approximately 1.6 .mu.m and the width of each 
micro-cup is approximately 0.6 .mu.m. A disk 30 cm in diameter can consist 
of 50,000 recording turns. 
In accordance with FIG. 2, the turns SP.sub.1 to SP.sub.n constituting the 
disk groove are spaced at intervals between the first turn SP.sub.1 having 
the longest radius OA and the last turn SP.sub.n having the shortest 
radius OD. One sector of each turn is reserved for the purpose of 
recording signals other than the video image such as, for example, the 
image number information and the frame synchronization. This sector is 
represented by the portion BC of the turn SP.sub.1, the video image and 
the line synchronization being recorded on the portion AB in accordance 
with known techniques, with or without image interlacing. 
The cartographic indicator system in accordance with the invention is 
intended to form the geographical map image corresponding at each instant 
to a well-defined region traversed by the aircraft with a representative 
point corresponding to the aircraft position and indicated with a high 
degree of precision. The map is oriented in a predetermined direction, for 
example in the direction of the geographical meridians corresponding to 
the vertical axis of symmetry of the display screen (North representation 
at the top of the image, vertical North-South axis) or the direction of 
the course of the aircraft in the same direction (Course representation at 
the top, vertical route). In consequence, the map image must be capable of 
undergoing three independent movements: vertically in the direction of the 
Y-axis and horizontally in the direction of the X-axis (cartesian 
movements) and angularly at .theta. (polar movement for the top Course 
representation). 
In order to obtain these results, the map is recorded zone by zone. The 
zones are successive in one of the reference cartesian directions such as 
the Y-axis and overlap partially from one zone to the next in the second 
reference direction X. 
FIGS. 3 and 4 illustrate the method adopted for subdividing the map into 
zones at the time of recording. This operation is performed in accordance 
with known techniques by means of a television camera, the map being 
placed on a table which is displaced along the X and Y axes. The direction 
Y corresponds to the direction of the geographical meridians. The map OTVG 
is considered as subdivided into two sets of adjacent bands parallel to 
one of the reference directions, the sets of bands being relatively 
displaced in the second reference direction so that the bands overlap to a 
partial extent from one band to the next. A first band B1 corresponds to 
the area OEFG, the second band B2 corresponds to the area MNPQ containing 
the area MEFQ which is common with the first band, and so on. The 
odd-numbered bands B1, B3 . . . form the first set and the even-numbered 
bands B2, B4 . . . form the second set. The double subdivision or map 
breakdown produced by these bands has been differentiated by indicating 
the odd-numbered bands B1, B3 . . . in full lines and the even-numbered 
bands B2, B4 . . . in dashed lines. Recording is carried out in a 
line-by-line scan, the lines being in the direction X at right angles to 
the direction of the bands. The successive zones (each zone corresponds to 
one television image of the recording) can be picked-up by passing from 
one band to the next in the direction of the X-axis or else by first 
recording the contents of the band B1 followed by the contents of the band 
B2 and so on in the direction of the Y-axis. The version just mentioned is 
shown in FIGS. 3 and 4 which show two successive zones Zj and Zj+1 of the 
band B1, each zone being constituted by n scanning lines. One image 
recorded on one turn of the video disk corresponds to each zone. Recording 
of the band B1 is represented by a segment PL1 on the disk; the segment 
PL2 corresponds to the following band B2 and so on in sequence. If the 
width of the bands in the direction X is designated by the letter D, the 
overlap is preferably chosen so as to be equal to D/2 for reasons of 
symmetry. The overlap makes it possible in cooperation with the 
intermediate memory to ensure continuous display on the indicator at the 
time of zone traversal as will become apparent hereinafter. 
The intermediate memory 8 has a predetermined capacity for storage of a 
plurality of base images, the base image being intended for visual 
display. The number of memory cells is equal to N. l.p.b.c., where N is 
the number of base images, l is the number of lines of the base image and 
p is the number of points per line, b is the number of luminance bits and 
c designates the number of chrominance bits in the case of a color 
display. The memory 8 can be of the semiconductor type with either random 
or sequential access to writing and to reading of data stored in lines and 
points by lines. The number of layers of N.l.p points is a function of the 
number of bits b and c. For example, four layers make it possible to 
record four luminance levels and twelve chrominance values. The capacity 
of the memory 8 takes into account the image rotation to be introduced by 
the course parameter .theta. (navigation on a course "at the top") as 
shown in FIG. 5; the number r of lines stored per layer corresponds at 
least to the number which is necessary in order to contain the information 
of the diagonal line D1 of the image, the dimensional value of which is 
given by .sqroot.L.sup.2 +H.sup.2, where L is the width of the image 
displayed and H is its height. In the example shown in the figure, it is 
considered that the number r of lines corresponds to one or a number of 
"zone Zj" images recorded on the disk and that the dimension D of the 
bands corresponding to the width of the lines is chosen so as to be equal 
to three times the width L of the displayed image; in the case of a ratio 
L/H equal to 4/3 for example, r=5/3 1 and the number N of base images 
stored in the memory will be equal to five. 
The number r of stored lines is greater than the number l of the displayed 
image, thus providing a range of displacement for the movement of the 
displayed map along the Y-axis. Depending on the direction of motion, the 
memory is refreshed with data derived from the adjacent zone Zj-1 or Zj+1. 
Thus, in the case of a movement on the Y-axis in the direction OY, the 
zone Zj+1 will be progressively introduced in memory instead of the top 
lines on the zone Zj which have become useless. This result is obtained by 
reading the corresponding turns of the video disk and selecting the l 
useful lines in the successive recorded images. 
Similarly, it is apparent that the capacity of the intermediate memory 
permits a range of variation in the case of the movement along the X-axis 
which can be determined by 3L-2h, where h is equal to HL/D1.sup.2 in order 
to ensure that the image to be displayed remains within the stored zone 
irrespective of the course .theta.. When one of these lateral limits has 
been reached, it becomes necessary to refresh the memory with the data 
corresponding to the following overlap zone. Thus, in the case of a 
movement in the direction OX, the data of the zone Zj of the band Bk+1 are 
extracted and replaced by those of the zone Zj of the band Bk. Taking the 
band overlap into account, the refresh operation corresponds to the first 
half of the lines and does not produce any discontinuity of display. 
The stored lines each comprise 3p points by analog-to-digital conversion 
and coding at 9 of the signals derived from the video disk. As a function 
of the parameters X, Y and .theta. which represent the flight evolution of 
the aircraft, the computation and management unit 5 determines the 
fractions of lines to be extracted from the memory 8 in order to 
constitute the moving-map image to be displayed for the readout operation, 
as well as the lines or fractions of lines of successive zones to be 
introduced at the time of writing in order to refresh the memory 
continuously. 
In the diagram of FIG. 6, the memories are shown in greater detail. In the 
video-disk or mass-memory device are grouped together the video disk 7 
with its circuit 15 for driving the disk in rotation at constant speed, 
the read head 16 and an associated control circuit 17 for controlling the 
positioning of the read head and the collection by optical reading of 
information recorded on the disk. The circuit 17 produces mechanical 
control of the radial positioning of the head 16 by means of a mechanical 
coupling M1 and electronic control of the instant of collection via the 
output S1. The instant of collection may be located at the beginning of a 
turn, namely on the first line of a recorded image or during a turn, 
namely on a predetermined line of a recorded image. The version last 
mentioned corresponds to the operation which consists in carrying out a 
fine relative displacement along the Y-axis at the level of the video 
disk, the relative displacement zone by zone being produced by the 
mechanical drive M1. Line selection may be performed just as readily at 
the write input level of the intermediate memory in the case of disk 
reading at the beginning of each turn. Depending on the design solution 
adopted, corresponding control signals S2 and S3 are generated by the 
computation and management circuit 5; this circuit can be designed in the 
form of a microprocessor which receives the information SX, SY, S.theta. 
in digital form from an ancillary airborne computer (not shown). The 
processor 5 thus permits practically random access to the mass memory and 
the circuit 17 permits access to a particular image or to a particular 
image line. 
The intermediate memory is represented schematically by an addressing and 
writing circuit 18, an addressing and reading circuit 19, a sequencing 
circuit 20 and the memory 21 proper. The output S4 of the video disk is 
converted to digital representation point by point in the case of each 
line by the circuit 9 which carries out coding of the luminance and of the 
chrominance. The data S5 thus produced are transmitted to the circuit 18 
which associates with each coded point a memory address, the evolution 
algorithm of which is predetermined by the management processor 5 in the 
form of the signals S3. The sequencer 20 distributes the priorities of 
access to the memory in the form of periodic control signals S6, S7, S8. 
The read circuit 19 serves to collect images to be displayed at the rate 
of any television standard, the starting address in the memory being 
initialized by the management processor 5 and represented schematically by 
the connection S9. The output S10 of the intermediate memory is 
transmitted to the circuit 10 for reconstituting the video signal with the 
frame and line synchronization signals and the chrominance in order to 
supply the television monitor 3. 
Simultaneous display of symbols can be carried out, for example, by 
incrustation by means of the mixer 4. The symbol generator 2 is controlled 
by the output S11 of the processor 5 so as to deliver the signals of the 
various parameters to be displayed during flight. Data relating to 
identification of the different symbols and characters to be produced 
during the mission as well as their respective positions in the image are 
stored beforehand in a working memory 22. The aircraft reference mark can 
be produced, for example, at the center and at the bottom of the displayed 
image so that this latter may correspond mainly to the geographical region 
which is directed towards the front of the aircraft. 
Construction of the computation and management unit 5 and of the 
intermediate memory 8 is considered as carried out in accordance with 
known techniques. In particular, programming depends on the mode of 
subdivision and recording of zones and on the organization of the 
intermediate memory. The computing means such as a microprocessor receives 
the navigational data such as aircraft position (SX, SY), course (S8) as 
well as other data, in particular the speed SV of the aircraft and the 
choice made by the pilot in regard to the mode SM of North representation 
or Course "at the top". On the basis of these data, the pilot plots the 
coordinates X, Y of the center of the image to be displayed, the polar 
angle of the representation, and identifies the zones or portions of zones 
to be extracted from the video disk. 
By way of indication, FIG. 7 is a general arrangement diagram of the video 
disk control system. The information S20 relating to the image to be 
selected or in other words to the turn SPj on which said image is recorded 
is delivered by the processor 5 to an identification logic circuit 30 such 
as a bidirectional counter in which the datum S20 is compared with the 
corresponding information S21 delivered by the read head. The datum S21 
includes the image number written on a reserved portion BC of the turn 
(FIG. 2) and represents the radial position of the read head. The digital 
output of the comparator 30 is converted to an analog signal S22 which 
supplies a servo circuit 32 for radial positioning of the head 16. When 
the head is positioned on the desired turn SPj, the error signal S22 is 
reduced to zero and the circuit 30 delivers a read permission signal S23 
which initiates production of the output signal S4 of the read head. The 
other circuits shown in the figure relate to line selection in the 
recorded image, this selection being considered as effected at the level 
of the video disk. The radial locking information is transmitted to the 
processor 5 by the signal S21 or in an equivalent manner by the output of 
the circuit 30. As soon as radial positioning has been completed, the 
circuit 5 delivers the information relating to the line number to be 
selected to a bidirectional counter circuit 33. The output S4 of the video 
disk is transmitted to a circuit 34 for extraction of the frame and 
synchronization signals S25 and S26 respectively. The frame signal 
initiates counting of the synchronization signals until coincidence with 
the line number to be selected. At this instant, the output 27 initiates 
closure of the switching circuit 35, thus permitting transmission of the 
signal S4 on the downstream side towards the intermediate memory 8. The 
signal S27 also trips and resets the circuit 33 to zero. Similarly, the 
end of collection of the recording can be initiated by transmitting fresh 
line information in an image considered to the circuit 33 and producing 
after counting a reverse action of opening of the switching circuit 35. 
The cartographic indicator system hereinabove described permits of many 
variants in accordance with the characteristics explained in the 
foregoing. One of these variants consist in particular in recording zones 
Zj corresponding to the image to be displayed, the bands being of width L. 
In this context, the capacity of the intermediate memory can be reduced 
and correspond to three base images by collection of two zones along Y out 
of two successive bands. Management of the system is determined in 
consequence and results in more frequent refreshments of the intermediate 
memory and therefore in more numerous accesses to the video disk. The 
solution to be adopted therefore results from a compromise in order to 
achieve operational reliability with a limited capacity of the 
intermediate memory.