Automatic transference between real-time operation and post-processing in a GPS survey system

• US 5,841,026 A
• Filed: 05/15/1996
• Issued: 11/24/1998
• Est. Priority Date: 05/15/1996
• Status: Expired due to Term

• Current Assignee: Trimble Navigation Limited (Trimble Inc.)
• Original Assignee: Trimble Navigation Limited (Trimble Inc.)
• Inventors: Viney, Ian, Skoog, Paul N., Allison, Michael Timo, Kirk, Geoffrey R.
• Primary Examiner(s): Noori, Max H.
• Application Number:
  US08/647,701
• Time in Patent Office: 923 Days
• Field of Search: 73/178 R, 342/352, 342/357, 342/358
• US Class Current: 73/178.00R
• CPC Class Codes: G01C 15/00 Surveying instruments or accessories not provided for in groups G01C1/00 - G01C13/00
• CPC Class Codes: G01S 19/04 providing carrier phase data
• CPC Class Codes: G01S 19/44 Carrier phase ambiguity resolution; Floating ambiguity; LAMBDA [Least-squares AMBiguity Decorrelation Adjustment] method

Abstract

A centimeter level survey system includes reference base station and rover GPS units connected by a radio data link. Each includes recorders for the storage of raw measurement information including range, phase, cycle counts and time information. The rover unit is typically moved to points of interest during a survey while the base remains over a fixed, and known location. Generally, the base antenna is located to optimize a clear view of the sky. The rover is subject to interruption of the radio data link from the primary reference station. During periods that the rover is initialized and in contact with the primary reference station base station over the radio data link, the rover provides real time centimeter level position solutions to a survey user, otherwise, the rover records its raw measurements in a file that begins with the last valid initialization information and that ends with any newly reestablished initialization information. A post-processor is initialized by transferring the position filter states and covariance matrix of the real-time processor in the rover directly to the position filter of the post-processor, provided that continuous satellite tracking and no carrier cycle slips have occurred.

Claims

1. An improved survey system, including a reference base station for receiving signals from orbiting navigation satellites, a survey rover for computing a vector to the base station, a radio data link connected to provide measurement information from the primary reference station base station to the survey rover for real time centimeter level position solutions, and recorders at each of the primary reference station base station and the survey rover for recording data, the improvement comprising:

first means for detecting a loss of real time kinematic (RTK) initialization at the survey rover;

second means for detecting a loss of communication over the radio data link; and

third means connected to each of the first and second means and for recording a file on the survey rover recorder that begins with a last valid initialization information that existed before a loss of either said RTK initialization or said communication over said radio data link, that records raw measurement information of the survey rover during either of said losses, and that ends by recording the survey rover RTK initialization information when both said RTK initialization and said communication over said radio data link are restored.

2. The system of claim 1, further comprising:

post processing means connected to each of said reference base station and survey rover recorders and for computing centimeter level positions of the survey rover for periods of loss of either said RTK initialization of the survey rover or periods of loss of said radio data link.

3. The system of claim 2, further comprising:

backward initialization propagation means connected to the post processing means for computing centimeter level positions from the raw measurements collected in said file between said beginning and ending from backward in time propagation of said RTK initialization information included at said file ending.

4. A survey system, comprising:

a survey rover, reference base station and radio data link that, at a time t0, provide for raw measurement information and differential correction data to begin to be communicated from said reference base station over a radio data link to said survey rover;

means providing, at a time t1 following said time t0, an initialization of said survey rover that provides for the real time survey position solutions;

means providing at a time t2 following said time t1, a communication of said last valid initialization information just before said radio data link is broken at a time t3 that follows said time t2;

means for anticipating said loss of communication by constantly recording said initialization information and raw measurements in a circular buffer that is transferred as a history to a recording at time t3, wherein real time survey position solutions are not available after time t3, and initialization may be quickly lost thereafter;

means providing at a time t4 that follows said time t3, a re-establishment of said radio data link and continuation of said recording until a time t5 that follows said time t4 wherein said survey rover reestablishes its initialization or restarts real-time positioning at said time t5; and

means providing for copying said reestablished initialization information into said recording at time t5 and ending said recording;

wherein raw measurement information, including range, phase, cycle count and time measurements are recorded by said survey rover in said recording between said times t2 and t5.

5. A position domain method for recording raw measurement information from a survey rover having an unreliable radio data link to a reference base station, the method comprising:

at a time t0, said survey rover, reference base station and radio data link are placed in operation, providing for raw measurement information and differential correction data to begin to be communicated from said reference base station over said radio data link to said survey rover;

at a time t1 following said time t0, initializing said survey rover that provides for the real time survey position solutions;

at a time t2 following said time t1, communicating said last valid initialization information just before said radio data link is broken at a time t3 that follows said time t2;

anticipating said loss of communication by constantly recording said initialization information, position information and raw measurements in a circular buffer that is transferred as a history to a recording at time t3, wherein real time survey position solutions are not available after time t3, and initialization may be quickly lost thereafter;

at a time t4 that follows said time t3, reestablishing said radio data link and continuing said recording until a time t5 that follows said time t4 wherein said survey rover reestablishes its initialization or restarts real-time positioning at said time t5; and

copying said reestablished initialization information into said recording at time t5 and ending said recording;

wherein raw measurement information, including range, phase, cycle count and time measurements are recorded by said survey rover in said recording between said times t2 and t5.

6. A measurement domain method for initializing a post-processor of a survey system that collects survey information from a GPS-based reference station in communication with a GPS-based rover, wherein the communication between the reference station and the rover is subject to interruption, the method comprising the steps of:

checking the condition of a communication channel between a survey reference station and a survey rover;

if said communication channel is interrupted, beginning the recording of GPS data and integer ambiguities from the position filter of a real-time position processor in said survey rover;

transferring said GPS data and integer ambiguities to a survey post-processor;

checking said GPS data and integer ambiguities for whether the associated GPS satellites have been continuously tracked and whether carrier cycle slips have occurred;

if said associated GPS satellites have been continuously tracked and no carrier cycle slips have occurred, marking said GPS data and integer ambiguities for said survey post-processor as valid for each associated GPS satellite;

checking to see if four or more satellites have thus been marked as providing valid data; and

if four or more GPS satellites have been marked as providing valid data, then initializing said post-processor directly by starting with position filter states and covariance matrix supplied by said real-time processor in said CPS data and integer ambiguities.

7. A survey system, comprising:

a GPS-based survey rover for visiting a plurality of positions to be determined by a survey;

a GPS-based reference station at a known location;

a data communication link for providing raw measurement information and differential correction data from the reference station to the survey rover;

means for checking the condition of the data communication link;

means for beginning a recording of GPS data and integer ambiguities from a position filter of a real-time position processor in the survey rover if the data communication link is interrupted;

means for transferring said CPS data and integer ambiguities to a survey post-processor;

means for checking said CPS data and integer ambiguities for whether the associated CPS satellites have been continuously tracked and whether carrier cycle slips have occurred;

means for marking said GPS data and integer ambiguities for said survey post-processor as valid for each associated GPS satellite if said associated GPS satellites have been continuously tracked and no carrier cycle slips have occurred;

means for checking to see if four or more satellites have thus been marked as providing valid data; and

means for initializing said post-processor directly by starting with a set of position filter states and a covariance matrix supplied by said real-time processor in said GPS data and integer ambiguities if four or more GPS satellites have been marked as providing valid data.

8. The system of claim 7, further including:

a rover to reference station communication link that provides for less than continuous data logging at said reference station.

9. A survey system, comprising:

a reference base station for receiving signals from a satellite navigation positioning system and providing for a calculation and output of a sequence of satellite navigation position measurement information;

a communication link for transmitting said satellite navigation measurement information from the reference base station;

a survey rover for receiving said satellite navigation measurement information over the communication link and for determining a series of centimeter-level accurate position solutions from said satellite navigation measurement information;

a detector associated with the survey rover responsive to a loss of communication over the communication link; and

a recorder controlled by the detector to store a data record that begins with a last measurement data obtained during a last valid initialization that existed prior to any loss of reference-base-station to survey-rover communication and to also store a series of raw-measurement information of the survey rover;

wherein, when both the communication link and a real-time kinematic initialization are detected as having been restored, the recorder is switched from recording raw measurement information to record RTK initialization information in preparation for another interruption of the communication link.

10. The survey system of claim 9, further comprising:

a post processing system configured to compute centimeter level positions of the survey rover for periods of loss of either the RTK initialization or periods of loss of the communication link.

11. The survey system of claim 9, wherein:

the survey rover is further configured to detect a loss of real time kinematic (RTK) initialization at the survey rover, responsive to the loss of RTK initialization the survey rover recording data beginning with a last valid initialization information that existed prior to the loss of RTK initialization and additionally begins recording raw measurement information of the survey rover.

12. A measurement domain method for initializing a post-processor of a survey system that collects survey information from a GPS-based reference station in communication with a GPS-based rover, the method comprising the steps of:

checking the condition of a communication channel between a survey reference station and a survey rover;

recording GPS data and integer ambiguities from a position filter of a receiver in the survey rover if the communication channel is interrupted;

transferring the GPS data and the integer ambiguities to a survey post-processor; and

initializing the post-processor directly by starting with position filter states and covariance matrix supplied by the receiver in the GPS data and the integer ambiguities if four or more GPS satellites associated with the GPS data and the integer ambiguities have been continuously tracked and no carrier cycle slips have occurred.

20. The method of claim 12, further including the steps of:

checking the GPS data and the integer ambiguities for whether the associated GPS satellites have been continuously tracked and whether carrier cycle slips have occurred;

if the associated GPS satellites have been continuously tracked and no carrier cycle slips have occurred, marking the GPS data and the integer ambiguities for the survey post-processor as valid for each associated GPS satellite; and

checking to see if four or more satellites have been marked as providing valid data.

13. A survey system comprising:

a reference base station for receiving signals from a satellite navigation positioning system and providing for a calculation and output of a sequence of satellite navigation position measurement information;

a communication link for transmitting said satellite navigation measurement information from the reference base station;

a survey rover receiving the measurement information over the communication link and determining centimeter level position solutions

a detector associated with the survey rover responsive to a real time kinematic (RTK) initialization at the survey rover; and

a recorder controlled by the detector to store a data record that begins with a last measurement data obtained during a last valid initialization that existed prior to any loss of reference-base-station to survey-rover communication, wherein said data record includes a series of raw-measurement information of the survey rover;

wherein, when both the communication link and a real-time kinematic initialization are detected as having been restored, the recorder is switched from recording raw measurement information to record RTK initialization information in preparation for another interruption of the communication link.

14. The survey system of claim 13, wherein:

the survey rover is further configured to detect a loss of communication over the communication link and responsive to the loss of communication the survey rover recording data beginning with a last valid initialization information that existed prior to the loss of communication and additionally begins recording raw measurement information of the survey rover.

15. The survey system of claim 14, wherein:

when both the RTK initialization and the communication link are restored, the survey rover stops recording raw measurement information and records RTK initialization information.

16. The system of claim 15, further comprising:

a post processor configured to compute centimeter level positions of the survey rover for periods of loss of either the RTK initialization or periods of loss of the communication link.

17. The system of claim 16, further comprising:

a backward initialization propagator connected to the post processor for computing centimeter level positions from information recorded after the loss of either the communication link or of the RTK initialization.

18. A position domain method for recording raw measurement information from a survey rover, the method comprising:

a reference base station communicating raw measurement information and differential correction data over a radio data link to the survey rover;

initializing the survey rover that provides for the real time survey position solutions;

recording initialization information, survey position solutions and raw measurement information in a buffer;

if the radio data link is broken, then transferring a last valid initialization information and the survey position solutions from the buffer to a file; and

after the survey rover reestablishes its initialization or restarts real-time positioning, copying the reestablished initialization information into the file.

19. The method of claim 18, wherein:

the raw measurement information includes range, phase, cycle count and time measurements.