Real time video perspective digital map display method

• US 4,660,157 A
• Filed: 11/13/1984
• Issued: 04/21/1987
• Est. Priority Date: 10/02/1981
• Status: Expired due to Term

• Current Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Original Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Inventors: Bascle, Kent P., Pearce, Jeffrey B., Beckwith, Paul B.
• Primary Examiner(s): Gruber, Felix D.
• Application Number:
  US06/670,933
• Time in Patent Office: 889 Days
• Field of Search: 364/521, 364/522, 364/518, 364/731, 358/103
• US Class Current: 345/421
• CPC Class Codes: G06T 15/20 Perspective computation
• CPC Class Codes: G09B 9/301 by computer-processed or -generated image

Abstract

A digital system for producing a real-time visual display in perspective of the terrain over which an aircraft is passing on the basis of compressed digital data stored on a cassette tape includes a perspective processor for transforming the addresses of points in a two-dimensional data pattern to the addresses these points occupy in a three-dimensional scene and for a filing in points between the transformed points to provide a complete display of the terrain in perspective.

Claims

1. A method for storing and retrieving digital information in a system producing a perspective display, comprising the steps of:

storing digital data representing a two-dimensional pattern of elevation information in addressable memory locations of a memory;

generating signals representing the parameters of the desired perspective display including the height and location of the viewing point and the angle of the display with respect to the two-dimensional pattern;

reading elevation data from selected addressable memory locations of said memory through the generation of address signals and applying said address signals to said memory; and

transforming the address of each elevation data read out of said memory from the address of that point in the two-dimensional pattern to the address of a respective pixel position in the perspective display.

2. A method according to claim 1, wherein said digital data is stored in said memory with said pattern having a fixed orientation and wherein said reading step includes selectively generating said address signals so as to read out pattern information in a direction which may be selectively different from said fixed orientation.

3. A method according to claim 2, wherein said transforming step includes generating a signal Δ

E representing the difference in height between the viewing point of the perspective display and each elevation point in said elevation pattern, generating a signal R representing the distance parallel to said fixed orientation between each elevation point and the viewing point in said two-dimensional elevational pattern, and generating a signal Δ

W representing the distance between each elevation point and a line through the viewing point parallel to said fixed orientation.

4. A method according to claim 3, wherein said transforming step further includes generating transformed addresses a,b for each pixel according to the relationship:

##EQU9## where α

is the angle of the perspective display with respect to said two-dimensional elevational pattern and K is a constant.

5. A method for storing and reading out digital information use in generating a perspective display of terrain over which a vehicle is moving on the basis of digital data representing a two-dimensional elevation terrain pattern which is addressable in relation to the coordinate position of each point in said terrain pattern, comprising the steps of:

storing said elevation data representing at least a portion of the terrain pattern of the terrain over which the vehicle is passing in memory;

providing signals representing the angle of heading of said vehicle with respect to a fixed geographical orientation, the angle of the perspective display with respect to said two-dimensional elevation terrain pattern, and the elevation and current position of said vehicle with respect to said terrain;

reading elevation data out of said memory through the generation of address signals and the application of said address signals to said memory; and

transforming, in response to said provided signals, the address of each point read out of said memory from the address of the point in the two-dimensional terrain pattern to the address of a respective pixel position in said perspective display.

6. A method according to claim 5, wherein said transforming step includes generating a signal Δ

E representing the difference in elevation between the vehicle and each elevation point in said terrain pattern, generating a signal R representing the distance parallel to the vehicle heading between each elevation point position and the vehicle position in said terrain pattern, and generating a signal Δ

W representing the distance between each elevation point and a line through the vehicle position parallel to the vehicle heading in said terrain pattern.

7. A method according to claim 6, wherein said transforming step includes further generating transformed addresses a,b for each point according to the relationships ##EQU10## where α

is the angle of the perspective display with respect to said two-dimensional elevational terrain pattern and K is a constant.

8. A method according to claim 5, wherein said terrain pattern of data is stored in said memory with a fixed geographical orientation, and said reading step includes selectively generating said address signals so as to read out pattern information in a direction which may be selectively different from said fixed geographical orientation.

9. A method according to claim 5, wherein said terrain pattern of data is stored in said memory with a north-up orientation, wherein said reading step includes selectively generating said address signals so as to scan said elevation data in said memory either in a north-south or an east-west direction depending on which is closest to the direction of heading of the vehicle with respect to said terrain.

10. A method according to claim 5, wherein said reading step includes means for selectively generating said address signals so as to scan an area of said memory in successive lines which extend from a line through the point position corresponding to the position of the vehicle in the general direction of heading of the vehicle with respect to the terrain.

11. A method according to claim 5, wherein said reading step includes selectively generating said address signals so as to scan a generally diamond-shaped area of said memory, said area being positioned within said memory with one edge thereof being substantially transverse to the direction of vehicle heading with respect to said terrain pattern and the scanning of said area being in the direction parallel or transverse to the geographical orientation of said data in the scene memory, whichever makes the smallest angle with said vehicle heading.

12. A method for generating a perspective display of terrain over which a vehicle is moving, comprising the steps of:

storing, in memory, digital data representing a two-dimensional elevation terrain pattern which is addressable in relation to the coordinate position of each elevation point with respect to a selected geographical orientation;

providing signals representing the heading angle of said vehicle with respect to said selected geographical orientation, the angle of the desired perspective display with respect to said two-dimensional elevation terrain pattern, and the elevation and current position of said vehicle with respect to said terrain;

reading-out of memory, in response to said provided signals, elevation data for respective ones of said elevation points through the generation of address signals and the application of said address signals to said memory;

in response to said provided signals, transforming the address of each point read out of said scene memory from the address of that point in memory to the address of a respective pixel position in said perspective display;

storing the elevation data read out of said memory in a matrix of memory positions in a display memory, which form storage locations corresponding to said transformed addresses; and

displaying the elevation data stored in said display memory to produce said perspective display.

13. A method according to claim 12, further including

storing the data read out of said memory including the transformed address of each elevation in storage locations of a buffer storage corresponding to the storage locations occupied by said elevation data in said memory;

and

transferring said data from said buffer storage to storage locations in said display memory in accordance with said transformed address.

14. A method according to claim 13, wherein said reading-out step includes selectively generating said address signals so as to scan a generally diamond-shaped area of said memory along lines substantially parallel or transverse to said selected geographical orientation depending on which makes the smallest angle with the vehicle heading, said area being positioned within said memory with one edge thereof transverse to said vehicle heading.

15. A method according to claim 13, wherein said reading-out step includes selectively generating said address signals so as to scan a generally diamond-shaped area of said memory along parallel lines substantially in the direction of the heading of the vehicle.

16. A method according to claim 15, wherein said buffer storage includes a column buffer memory having a plurality of columns for storing respective lines of data read out of said memory by said reading-out step in positions corresponding to the locations of said data in said memory.

17. A method according to claim 16, wherein each column in said column buffer memory has a capacity to store data associated with at least the number of points which occupy the diagonal of said generally diamond-shaped scan area of said memory, and further including the steps of storing the address locations for each column of said column buffer memory at which data begins and ends and, in response to said address locations storing step, reading plural data from adjacent columns of said column buffer memory.

18. A method according to claim 16, wherein said transferring step includes reading out plural data including the transformed addresses thereof in groups from adjacent columns of said column buffer memory by scanning said columns, in response to the data read out of said column buffer memory, generating additional elevation data representing data occupying positions extending along lines between data points of each group in accordance with the transformed addresses thereof, and transmitting said data and said additional data in said display memory.

19. A method according to claim 18, wherein said transferring step includes inhibiting, in response to the elevation data of each pixel to be transferred to said display memory, such transfer in connection with any pixel along a given column in said matrix of memory positions of said display memory which has an elevation value which is less than the elevation value of a pixel from the same column which has already been transferred to said display memory.

20. A method according to claim 19, wherein said inhibiting step includes storing in a column max memory an elevation value for each column of data stored in said display memory comparing the elevation value for each point read out of said column buffer memory and for each point generated by said additional data generating step with the elevation value stored in the column max memory for that column in which the data is to be written into said display memory, in response to said comparing step, storing, in the column max memory, the elevation value of the point when that value is greater than the value previously stored and inhibiting transfer of said data to said display memory when the elevation value thereof is less than that previously stored.

21. A method according to claim 18, wherein said additional data generating step includes storing the transformed addresses of two adjacent points, incrementing one of said addresses in first and second coordinate directions toward said other address by calculated stepping values, generating an additional data value at each incremented step, and controlling the storing of transformed address of the next points read out of said column buffer memory when the one address has been incremented until it corresponds to said other address.

22. A method according to claim 21, wherein said storing step includes storing the transformed addresses of four adjacent points read out of said column buffer memory, and said incrementing step includes comparing said addresses in predetermined combinations of pairs and incrementing said addresses in said predetermined combinations of pairs only when said comparison thereof indicates that the one address of the pair has a selected relationship to the other address.

23. A method according to claim 22, wherein said comparing step includes determining whether the line extending between the pair of points will face in a predetermined direction with respect to the orientation of data in said display memory.

24. A method according to claim 13, wherein said transferring step includes writing into said display memory along successive scanning lines only those data values which represent a different value of slope from the previous data value stored in said display memory on the same scanning line.

25. A method according to claim 24, wherein said displaying step includes reading pixel data out of said display memory, including the step of generating pixels for storage locations containing zero information in accordance with the value of the last pixel read out along the same scanning line.

26. A method according to claim 25, wherein said display memory includes first and second display memories, and said further including the step of writing pixel data into one of said first and second display memories while pixel data is being read out of the other.

27. A method for storing and reading out digital information for use in generating a real-time perspective display of terrain over which a vehicle is moving on the basis of stored digital data representing a two-dimensional elevational terrain pattern and signals indicating the instantaneous heading, geographic location and elevation of the vehicle and the desired angle of view of the resultant perspective display, comprising the steps of:

storing in a scene memory said digital data in addressable coordinate positions related to a selected geographic orientation of the terrain;

in response to signals representing heading, geographic location and angle of view, reading data out of said scene memory through the generation of address signals to address a selected area of said scene memory on the basis of the heading and geographic location of the vehicle and the desired angle of view with respect to the terrain represented by said digital data;

in response to signals representing heading, elevation, geographic location and angle of view, transforming the address of each data value read out of said scene memory from the address of its associated point in the two-dimensional terrain pattern to the address of a respective pixel in said perspective display; and

in response to the transformed addresses, generating a real-time perspective display of said terrain.

28. A method according to claim 27, wherein said transforming step includes varying said transformed addresses in response to selected variations in the signal representing the desired angle of view.

29. A method according to claim 27, wherein said transforming step includes generating a signal Δ

E representing the difference in elevation between the vehicle and each point in said terrain pattern, generating a signal R representing the distance parallel to the vehicle heading between each point position and the vehicle position in said terrain pattern, and generating a signal Δ

W representing the distance between each point and a line through the vehicle position parallel to the vehicle heading in said terrain pattern.

30. A method according to claim 29, wherein digital data stored in said scene memory represents, for each point in the terrain, an elevation value E_i equal to the actual elevation of that point reduced by a base elevation E_b, and said step of generating the signal Δ

E includes multiplying the elevation value E_i read from said scene memory by a scale factor S_f and adding to the result of said multiplication the base elevation E_b, and subtracting the output of said multiplying step from the signal representing the elevation of said vehicle.

31. A method according to claim 29, wherein said transforming step includes generating transformed addresses a,b for each point according to the relationships ##EQU11## where α

is the desired angle of view with respect to the horizontal and K is a constant.

32. A method according to claim 27, wherein said reading-out step includes selectively generating said address signals so as to scan a generally diamond-shaped area of said scene memory, said area being positioned within said scene memory with one edge thereof being substantially transverse to the direction of vehicle heading with respect to said terrain pattern and the scanning of said area being in the direction parallel or transverse to the geographical orientation of said data in the scene memory, whichever makes the smallest angle with said vehicle heading.

33. A method according to claim 27, wherein said displaying step includes providing a column buffer memory having a plurality of columns for storing respective lines of data, including both elevation data and the transformed address of each point read out of said scene memory by said read-out means, in positions corresponding to the locations of said points in said scene memory, in response to groups of the data read out of said column buffer memory, generating additional data representing the elevation and addresses of points extending along lines between the points of each group in accordance with the transformed address thereof, and storing in a display memory, the elevation data of points processed by said step of generating additional data and points read out of said column buffer memory at locations corresponding to the transformed addresses of said points.

34. A method according to claim 33, wherein said displaying step further includes transferring data into said display memory by scanning said display memory in successive lines beginning with pixel data representing the bottom of the display, the storage locations in each line of pixel data in the display memory forming columns with the corresponding positions in the other lines.

35. A method according to claim 34, wherein said transferring step includes inhibiting, in response to the elevational data of each point to be transferred to said display memory, such transfer in connection with any pixel along a given column of said display memory which has an elevational value which is less than the elevational value of a pixel of the same column which has already been transferred to said display memory.

36. A method according to claim 35, wherein said inhibiting step includes storing, in a column max memory, an elevation value for each column of data stored in said display memory, comparing the elevation value for each point read out of said column buffer memory and for each point generated by said additional data generating step with the elevation value stored in the column max memory for that column in which the pixel is to be written into said display memory, in response to said comparing step, storing, in the column max memory, the elevation value of the pixel when that value is greater than the value previously stored and inhibiting transfer of said pixel value to said display memory when the elevation value thereof is less than that previously stored.

37. A method according to claim 33, wherein said additional data generating step includes storing the transformed addresses of two adjacent points, incrementing one of said addresses in first and second coordinate directions toward said other address by calculated stepping values, generating an additional data value at each incremented step, and controlling the storage of transformed addresses of the next points read out of said column buffer memory when the one address has been incremented until it corresponds to said other address.

38. A method according to claim 37, wherein said storing step stores the transformed addresses of four adjacent points read out of said column buffer memory, and said incrementing step includes comparing said addresses in predetermined combinations of pairs, and incrementing said addresses in said predetermined combinations of pairs only when the comparison thereof indicates that the one address of the pair has a selected relationship to the other address.

39. A method according to claim 38, wherein said comparing step includes determining whether the line extending between the pair of points will face in a predetermined direction with respect to the orientation of data in said display memory.

40. A method according to claim 33, wherein said displaying step further includes generating, with respect to each data value read out of said column buffer memory and each data value generated by said additional data generating step, the slope at the point of the terrain represented by that data value on the basis of the data values around that point, and transferring said slope data into said display memory at addresses provided by said additional data generating step in successive lines.

41. A method according to claim 40, wherein said slope generating step includes comparing each value of slope which is generated with the slope value previously generated for the preceding point, and in response to said comparing step, controlling the storage in said display memory only that data which represents a change in slope on a given scanning line in said display memory.

42. A method according to claim 41, wherein said display step includes reading pixel data out of said display memory, including generating pixels for storage locations containing zeros in accordance with the value of the last non-zero pixel read out along the same scanning line.