Global Positioning Systems

Precise Lightweight GPS Receiver (PLGR) The PLGR+ receiver with 999 waypoints has seen two upgrades since it was made available in August, 1994. PLGR-95 is an upgrade to NMEA and SC-104 compatibility for differential input WHILE IN Y-CODE MODE, and includes the capability to remove display pages to avoid users inadvertently changing configuration. PLGR-96 will include a robust set of enhancements including all of PLGR -95 plus area determination, and precise azimuths for both horizontal and vertical users.

PPS user group meeting September 2005 in Denver, Colorado. Over 20 Federal agencies authorized for PPS attended this conference and received briefings from the Pentagon, the National Security Agency, and Space Command on policy, crypto key access and COMSEC, and GPS operations and status.

Frequently Asked Questions:

• Terms: RTCM SC-104 = Radio Technical Commission for Marine Services, Special Committee 104; recommended the defined standard for the GPS correction message.
• Availability: Continuous PPS service guarantees 16 meters spherical error probable.
• Improvements: Can differential improve the PPS position? Until recently, no, because PPS is not a pseudo-range position determination. PLGR-95 and the Trimble Centurion have developed RTCM SC-104 compatibility for real-time use of broadcast correctors to improve the solution to 1-2 meters. PLGR-96 using WAGE will position to about 4 meters without differential input, but retains SC-104 capability if desired.
• Statistics: Autonomous PPS is a relative on-the-fly service without absolute reference or confidence statistics. If a data point must attach Position Dilution of Precision (PDOP) values, then the user should operate in either the SPS environment with differential, or PPS with a differential link.
• Metadata: PDOP or Figure of Merit (FOM), collection time(s), Space Vehicles (SVs) used, and dates would be valuable additional metadata elements to complement the ASCII data stream downloaded from the GPS receiver.
• Output: PLGR+ via serial port (RS-232), ASCII download via Mission Planning Software (laptop), or NMEA real-time to another piece of equipment. Trimble Centurion uses the PFinder software and output protocols.