Global positioning system having postprocessed realtime corrected data

• US 5,973,639 A
• Filed: 09/23/1997
• Issued: 10/26/1999
• Est. Priority Date: 09/23/1997
• Status: Expired due to Term

• Current Assignee: Trimble Navigation Limited (Trimble Inc.)
• Original Assignee: Trimble Navigation Limited (Trimble Inc.)
• Inventors: Biacs, Zoltan, Farmer, Dominic
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): DRUMMOND, DEVIN E
• Application Number:
  US08/935,576
• Time in Patent Office: 763 Days
• Field of Search: 342/357
• US Class Current: 342/357.31
• CPC Class Codes: G01S 19/09 providing processing capability normally carried out by the receiver
• CPC Class Codes: G01S 19/41 Differential correction, e.g. DGPS [differential GPS]
• CPC Class Codes: G01S 19/52 Determining velocity

Abstract

A method for determining an improved position fix by performing postprocessing on a realtime differentially corrected GPS position. A remote rover unit containing a GPS receiver is used to determine a differentially corrected position according to measured pseudoranges and realtime pseudorange correction vectors is broadcast by a base station. The rover unit applies realtime corrections to measurements to determine a more accurate realtime differential position. It then stores the realtime differential position and the realtime pseudorange correction vector. Subsequently, postprocessing is performed to determine a postprocessed pseudorange correction vector. A difference vector representing the difference between the realtime pseudorange correction vector and the postprocessed pseudorange correction vector is then determined. This difference vector is applied to the realtime differential position to calculate a more accurate, improved position fix. This same process can be applied to determine velocities as well.

Claims

1. A method for determining a position by performing postprocessing of a realtime differential GPS position, comprising the steps of:

receiving a measured pseudorange signal by a GPS receiver in a remote unit from a GPS satellite;

receiving a base station correction signal by the GPS receiver in the remote unit from a base station fixed at a known location;

calculating a realtime pseudorange correction vector based on the measured pseudorange signal and the base station correction signal, wherein the realtime pseudorange correction is calculated by the remote unit in the field;

adjusting non-differential measurements according to the realtime pseudorange correction vector to determine a realtime differential position;

storing the realtime differential position and the realtime pseudorange correction vector in a memory of the remote unit;

performing postprocessing to determine a postprocessed pseudorange correction vector;

adjusting the realtime differential position as a function of a difference between the realtime pseudorange correction vector and the postprocessed pseudorange correction vector to produce a postprocessed realtime differential GPS position;

displaying the postprocessed realtime differential GPS position.

3. The method of claim 1, further comprising the steps of:

receiving a realtime pseudorange rate correction vector;

adjusting a non-differential pseudorange rate measurements according to the realtime pseudorange rate correction vector to determine a realtime differential velocity;

storing the realtime differential velocity and the realtime pseudorange rate correction vector;

performing postprocessing to determine a postprocessed pseudorange rate correction vector;

adjusting the realtime differential velocity as a function of a difference between the realtime pseudorange rate correction vector and the postprocessed pseudorange rate correction vector to produce a postprocessed realtime differential GPS velocity;

displaying the postprocessed realtime differential GPS velocity.

4. The method of claim 1 further comprising the step of simultaneously adjusting the realtime differential position with a plurality of sets of base station data.

2. The position computation uses pseudoranges, the velocity computation uses pseudorange rates (doppler). Equivalently we use PRC and RRC (range rate corrections), for correcting real time differential positions and velocities to post-processed differential positions and velocities.

5. A method for determining improved positions by performing postprocessing on realtime differential GPS positions, comprising the steps of:

reading data that was stored in the field, comprising realtime differential positions and realtime measurement corrections, wherein a remote rover unit containing a GPS receiver and a memory is used to process and store the realtime differential positions and the realtime measurement corrections;

reading a database containing GPS information generated from at least one base station;

calculating postprocessed measurement corrections according to the GPS information from the database;

adjusting the realtime differential positions according to the realtime measurement corrections and the postprocessed measurement corrections to determine the improved positions;

outputting the improved positions.

6. The method of claim 5, further comprising the steps of:

reading data that was stored in the field, comprising realtime differential velocities and realtime measurement corrections corresponding to the velocities;

reading a database containing GPS information generated from at least one base station;

calculating postprocessed measurement corrections according to the GPS information from the database;

adjusting the realtime differential velocities according to the realtime measurement corrections and the postprocessed measurement corrections to determine improved velocities;

outputting the improved positions.

7. The method of claim 5, further comprising the step of simultaneously adjusting the realtime differential position with a plurality of sets of base station data.

8. An apparatus for determining a postprocessed position by performing postprocessing on a realtime differential GPS position, comprising:

an input/output interface for accepting a realtime differential position and a realtime pseudorange correction vector that was processed and stored by a rover unit while in the field, wherein the rover unit is used to determine the non-differential position, determine the realtime differential position, and store the realtime differential position and the realtime pseudorange correction vector;

a memory coupled to the input/output interface for storing computer code instructions relating to a GPS postprocessing procedure;

a mass storage device coupled to input/output interface for storing GPS information generated by a base station;

a processor coupled to the input/output interface that performs postprocessing on the GPS information according to the computer code instructions to determine a postprocessed pseudorange correction vector, wherein the postprocessed position is determined by applying a difference vector, representing a difference between the realtime pseudorange correction vector and the postprocessed pseudorange correction vector, to the realtime differential position.

9. The apparatus of claim 8, wherein the processor performs postprocessing on the GPS information according to the computer code instructions to determine a postprocessed velocity correction vector, wherein a postprocessed velocity is determined by applying a difference vector, representing a difference between a realtime velocity correction vector and a postprocessed velocity correction vector, to the realtime differential velocity.

10. The apparatus of claim 8, wherein the processor simultaneously adjusts the realtime differential position with a plurality of sets of base station data stored in the mass storage device.