HEADING ERROR COMPUTER

• US 3,683,378 A
• Filed: 05/29/1969
• Issued: 08/08/1972
• Est. Priority Date: 05/29/1969
• Status: Expired due to Term

• Current Assignee: William L. Polhemus
• Original Assignee: William L. Polhemus
• Inventors: William, L. Polhemus
• Primary Examiner(s): Malcolm F. Hubler
• Application Number:
  US04/829,062
• Time in Patent Office: 1,167 Days
• Field of Search: 235/150.2,150.25,150.26 343/7ED
• US Class Current: 342/107
• CPC Class Codes: G01S 1/02 using radio waves G01S19/00 takes precedence
• CPC Class Codes: G06G 7/78 for direction-finding, locating, distance or velocity measuring, or navigation systems

Abstract

Apparatus for electronically and/or electromechanically computing the heading error angle of the heading or directional sensor of a ship or aircraft equipped with navigation systems having a mapping radar and/or electronic, optical or other viewing service and a computer with offset sighting capability; the apparatus being also capable of averaging several values of the computed heading error angle and computing the rate of drift or precession of the heading sensor. In addition, the averaging and drift rate computing sections of the computer can be used to mechanize calculation of average heading error and azimuth drift rate in aircraft which do not possess the required radar and offset sighting capabilities.

Claims

1. For use with a navigation system that has the capability of providing output signals corresponding to the coordinates of one radar sighting aimpoint with respect to a second radar sighting aimpoint and signals corresponding to the components of a displacement vector for linking first and second points on a radar display, a heading error computation system comprising means for computing the angle whose tangent is the quotient of the coordinates of said first radar sighting aimpoint with respect to the second radar sighting aimpoint, means for displacing and measuring the displacement of coordinates of said second radar sighting aimpoint by manual adjustment, means for summing the coordinates of said first radar aimpoint with respect to said second radar aimpoint and said manual displacement to coordinates of said second radar aimpoint along the same axes in two dimensional space, means for computing a second angle whose tangent is the quotient of said summed coordinates, and means for substracting said firstmentioned angle from said second angle to obtain the heading error angle.

2. The apparatus according to claim 1 further including means operatively asSociated with said subtracting means for averaging a plurality of values of said heading error angle.

3. The apparatus according to claim 2 wherein said averaging means comprises means for storing a cumulative average of heading error angles, means for forming the product of said cumulative average and a ratio which is a function of the number of values of the heading error angle included in said cumulative average, means for introducing another value of the heading error angle, means for forming the product of said second heading error angle and a ratio which is a function of the number of values in said cumulative average, and means for summing said first mentioned product and said second mentioned product to obtain a new value of said cumulative average, and means for storing said new value.

4. The apparatus according to claim 1 further including a drift rate computing unit comprising means for storing the average of a first set of heading error angle observations, means for subtracting a second set of averaged heading error angle observations from said first set to obtain the difference, and means for dividing said difference by the time elapsed between the acquisition of the two sets of averaged heading error angle observations to determine the drift rate of the heading error angle.

5. The apparatus according to claim 3 further including a drift rate computing unit comprising means for storing the average of a first set of heading error angle observations, means for subtracting a second set of averaged heading error angle observations from said first set to obtain the difference, and means for dividing said difference by the time elapsed between the acquisition of the two sets of averaged heading error angle observations to determine the drift rate of the heading error angle.

6. A heading error angle averaging unit comprising means for storing a cumulative average of heading error angles, means for forming the product of said cumulative average and a ratio which is a function of the number of values of said heading error angle included in said cumulative average, means for introducing another value of the heading error angle, means for forming the product of said other value of heading error angle and a ratio which is a function of the number of values in the said cumulative average, means for summing said first mentioned product and said second mentioned product to obtain a new value of said cumulative average, and means for storing said new value.

7. A drift rate computation unit for navigation systems capable of providing heading error angle observations comprising means for storing the average of a first set of heading error angle observations, means for subtracting a second set of averaged heading error angle observations from said first set to obtain the difference, and means for dividing said difference by the time elapsed between the acquisition of the two sets of averaged heading error angle observations to determine the drift rate of the heading error angle.

8. The apparatus according to claim 7 further including means for storing a cumulative average of said heading error angles, means for forming the product of said cumulative average and a ratio which is a function of the number of values of said heading error angle included in said cumulative average, means for introducing another value of the heading error angle, means for forming the product of said second mentioned heading error angle and a ratio which is a function of the number of values of said heading error in said cumulative average, means for summing said first mentioned product and said second mentioned product to obtain a new value of said cumulative average, and means for storing said new value.

9. For use with a vehicle navigation system that includes a dead reckoning navigation unit which continuously computes the present position of the vehicle being navigated using inputs from a gyro heading reference and a velocity sensor, a sighting computer which calculates the beariNg and distance from the computed present position of said vehicle to selected radar sighting aimpoints and a mapping radar system having a display screen provided with cross hair indices and capable of receiving and displaying radar signals on said screen and also capable of automatically driving said cross hair indices to a position on said radar display screen representing the computed position of a radar sighting aimpoint as calculated by said sighting computer and wherein said navigation system further includes means for providing output signals corresponding to the coordinates of a second radar sighting aimpoint with respect to the first radar sighting aimpoint and signals corresponding to the components of a vector on said radar display screen representing the displacement from said computed second display point to which said cross hair indices are driven automatically to said second mentioned radar sighting aimpoint by manually trimming said cross hairs, a heading error computation system comprising means for computing the angle whose tangent is the quotient of the coordinates of said first radar sighting aimpoint with respect to said second radar sighting aimpoint, and means for converting said components of said vector into the displacement coordinates of said second radar display point from said computed second display point, means for summing the coordinates of said first radar aimpoint with respect to said second radar aimpoint and the displacement coordinates of said computed second display point with respect to said second radar display point along the same axes in two dimensional space, means for computing a second angle whose tangent is the quotient of said summed coordinates, and means for subtracting said first mentioned angle from said second angle to obtain the heading error angle.

10. The apparatus according to claim 9 further including means connected to said subtracting means for averaging a plurality of values of said heading error angle.

11. The apparatus according to claim 10 wherein said averaging means comprises means for storing a cumulative average of heading error angles, means for forming the product of said cumulative average and a ratio which is a function of the number of values of the heading error angle included in said cumulative average, means for introducing another value of the heading error angle, means for forming the product of said other value of the heading error angle and a ratio which is a function of the number of values in the said cumulative average, and means for summing said first mentioned product and said second mentioned product to obtain a new value of said cumulative average, and means for storing said new value.

12. The apparatus according to claim 9 further including a drift rate computing unit comprising means for storing the average of a first set of heading error angle observations, means for subtracting a second set of averaged heading error angle observations from said first set to obtain the difference, and means for dividing said difference by the time elapsed between the acquisition of the two sets of averaged heading error angle observations to determine the drift rate of the heading reference system.

13. The apparatus according to claim 11 further including a drift rate computing unit comprising means for storing the average of a first set of heading error angle observations, means for subtracting a second set of averaged heading error angle observations from said first set to obtain the difference, and means for dividing said difference by the time elapsed between the acquisition of the two sets of averaged heading error angle observations to determine the drift rate of the heading reference system.

14. The method of measuring the error in the heading reference of a navigational system which includes a dead reckoning navigation unit that continuously computes the present position of the vehicle being navigated using inputs from a gyro heading reference and a velocity sensor, a sighting computer wHich calculates the bearing and distance from the computed present position of said vehicle to selected aimpoints and a mapping radar system having a display screen provided with cross hair indices and capable of receiving and displaying radar signals on said screen and also capable of automatically driving said cross hair indices to a position on said radar screen representing a radar sighting aimpoint as calculated by said sighting computer comprising the steps of:

a. selecting a radar sighting aimpoint whose position is known;

b. driving said cross hair indices to the position of said radar display screen representing said radar sighting aimpoint;

c. scanning said radar sighting aimpoint with said radar to obtain a radar display point on said radar screen representing the radar return signal from said radar sighting aimpoint;

d. aligning said cross hair indices with said radar return point on said radar screen to place the cross hairs precisely over the said radar return;

e. selecting a second radar sighting aimpoint whose position is known;

f. driving said cross hair indices to the position on said radar screen corresponding to said second radar sighting aimpoint as calculated by said sighting computer;

g. scanning said second radar sighting aimpoint with said radar to obtain a return signal from said second radar sighting aimpoint; and

h. measuring with respect to the return from the said second sighting aimpoint the difference in angular position between the position of said cross hair indices and the radar return from said second radar sighting aimpoint to obtain said error in said heading reference.