Ran a static test with the PM2’s last Saturday with setups on two NGS stations and correlated the results with the closest CORS station. The two setups and the CORS station formed a triangle with legs of 20.4, 13.1 and 9.7 miles. Each setup was at least five hours duration, five-second epoch to match the CORS station, with a minimum of five and maximum of seven satellites reported for a ten-degree cutoff on the mission-planning screen. I repeated the test this week with approximately the same parameters and similar results. Both sites were open sky with no obstructions at a 15-degree mask.

Holding the CORS site for horizontal and vertical control, I performed a minimally constrained adjustment. The computed position of the longest leg monument (20.4 miles) was surprisingly close to the published coordinates and elevation. The differences were:

N-S: 0.23 feet
E-W: 0.34 feet
Elevation: 0.12 feet

The thirteen-mile leg had results a little more than one-half of these differences.

I don’t plan on stretching the limits to these distances but I am pleased with the results. I am fairly new to GPS work and it is boosting my confidence in the equipment. Are other PM2 users having similar successes?


TH

You didn't say if the NGS stations were HARN stations, other GPS stations or NGS stations established using conventional survey methods? This would impact the level of agreement you would expect.

They were published stations. Position data was taken from NGS data sheets.

That sounds good...I bet your "error" is actually in the control you were tying into. With five hours shot twice, I bet you were more in the 2cm or better level. Ignoring the published values, how did your repeat vectors look?

JT

The accuracy of the NAD 83 horizontal coordinates of reference stations published by NGS on their data sheets is highly variable. If the published coordinates are for a CORS station they should be accurate at about the 1 cm (.03 ft) level, if they are HARN GPS stations the coordinates should be accurate to no worse than about 3 cm (about .1 ft) in most cases, although on a few occasions the can be in error by nearly .2 ft. The published NAD 83 coordinates of non GPS stations can easily be in error by up to 15 cm (.5 ft). Does the data sheets say whether or not rhe NGS stations you are connecting to are GPS stations or not?