High accuracy coordinate conversion method for air traffic control applications

• US 4,899,161 A
• Filed: 07/21/1988
• Issued: 02/06/1990
• Est. Priority Date: 07/21/1988
• Status: Expired due to Term

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: International Business Machines Corporation
• Inventors: Wasser, Barry, Morin, Wilfred W. Jr.
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): Issing, Gregory C.
• Application Number:
  US07/222,588
• Time in Patent Office: 565 Days
• Field of Search: 342/176, 342/178, 342/180, 342/450, 342/451, 342/456, 364/514, 364/516, 364/439, 364/456, 364/459, 364/731, 364/460, 364/461
• US Class Current: 342/451
• CPC Class Codes: G01S 13/91 for traffic control G01S13/93 takes precedence
• CPC Class Codes: G01S 7/2955 Means for determining the position of the radar coordinate system for evaluating the position data of the target in another coordinate system G01S7/24 takes precedence; sighting devices adapted for indirect laying of fire F41G3/16; inertial navigation G01C21/16

Abstract

A computer method is disclosed for accurately transforming multiple radar observations of aircraft into a common coordinate system for air traffic control applications. The method involves a transformation from radar observables of the target slant range, azimuth and altitude to the target position coordinates in a stereographic system plane for display. The method includes a conformal coordinate conversion process from geodetic to conformal spherical coordinates followed by a conformal stereographic projection process onto a system display plane. The resulting display of aircraft position on the system plane is more accurate than has been available in the prior art.

Claims

1. In an air traffic control system, including a plurality of radar stations, located on the surface of the Earth, operatively connected to a data processing system, a computer method for displaying the location of aircraft detected by said radar stations, comprising the steps of:

receiving the slant range, azimuth and altitude measurements of an aircraft at a first one of said radar stations;

computing the geodetic latitude and longitude of said aircraft in an ellipsoidal reference system;

computing the conformal latitude and longitude of the aircraft in a conformal spherical reference system;

projecting the conformal latitude and the longitude of said aircraft from said conformal spherical reference system to a system plane by means of a stereographic projection;

whereby aircraft positions are depicted accurately and all angles are preserved.

2. The method of claim 1, which further comprises:

said step of computing the geodetic latitude is an iterative step to obtain a more accurate value for the geodetic latitude of the aircraft.

3. A computer method for transforming multiple radar observations of aircraft into a common coordinate system for air traffic control, comprising the steps of:

initializing the radial distances to the radar and the aircraft and converting measured azimuth values to radians;

calculating the angular separation between the vectors from the Earth'"'"'s center to the radar and to the aircraft;

calculating the elevation angle of the aircraft above the radar geocentric horizontal;

calculating the radar azimuth relative to the radar;

initializing values of measured azimuth;

calculating the geocentric latitude of the aircraft;

calculating the longitudinal separation of the radar and the aircraft;

calculating the deviation from the normal at the aircraft;

calculating the geodetic latitude of the subtarget point of the aircraft;

calculating the geocentric latitude of the subtarget point of the aircraft;

calculating the radial distance to the subtarget point of the aircraft and to the aircraft;

repeating the steps starting with calculating the angular separation between the vectors from the Earth'"'"'s center to the radar and to the aircraft down to calculating the radial distance to the subtarget point of the aircraft and to the aircraft for several iterations, and then repeating the step of calculating the angular separation between the vectors from the Earth'"'"'s center to the radar and to the aircraft through calculating the geodetic latitude of the subtarget point of the aircraft for another iteration;

calculating the longitude of the subtarget point of the aircraft;

calculating the conformal latitude of the subtarget point of the aircraft;

calculating the x and y coordinates of the projection of the subtarget point of the aircraft in the stereographic display system plane;

displaying the position of the subtarget point of the aircraft at the x and y positions in the stereographic plane.

4. An air traffic control system, including a plurality of radar stations, located on the surface of the Earth, operatively connected to a data processing system, for displaying the location of aircraft detected by said radar stations, comprising:

means for receiving the slant range, azimuth and altitude measurements of an aircraft at a first one of said radar stations;

means for computing the geodetic latitude and longitude of said aircraft in an ellipsoidal reference system;

means for computing the conformal latitude and longitude of the aircraft in a conformal spherical reference system;

means for projecting the conformal latitude and the longitude of said aircraft from said conformal spherical reference system to a system plane by means of a stereographic projection;

whereby aircraft positions are depicted accurately and all angles are preserved.