|Subject:||[Info-gama] Effect of Free Gama Adjustment|
|Date:||Sat, 27 Mar 2004 11:19:24 -0800|
I am trying to derive the most reliabile absolute accuracy solution for a local survey network using Gama adjustment. The local survey network is a small survey network (4 to 6 points 40 to 60 metres apart) with direction and distance observations derived from photographic image. The directions have a standard deviation of about 8 minutes and the distances 5 centimetres. The Gama adjustment works well with a one "fix" and "Adj" point.
I observed multiple autonomous GPS positions and meaned them for each point. The autonomous GPS coordinates showed an average of 2.2 metres off the known (correct) absolute coordinates from the points - the range differences 1.0 to 4.0 metres. I seeded the Gama adjustment with these autonomous GPS coordinates as "free" and ran Gama. I understand that this treats the coordinates as unknown parameters and adjusts the free seeded coordinates. As a least square adjustment is done I presume this will minimize the residuals for these autonomous coordinates.
I did a compare of the adjusted Gama coordinates with the true coordinates. The mean of the comapred adjusted to true coordintes is 1.7 metres - the range differences 1.6m to 1.9m. This seems to be a good improvement.
My goal is to determine the best procedure for using/integrating the autonomous GPS positioning observations of multiple points of a local survey network along with the relative survey measurements of the local network. Has anyone else done any research similar to this? If so, I would be interested to see your summary results.
I will do some more testing. The automous GPS unit is only $150. I am looking for a way to optimize the global positioning and reliabitlity in using the autonmous receiver. I will also test this network using a WADGPS system that was recently rolled out to cover all of Canada. The receiver/communications device will be ported with a PDA device and the positions for the network will be meaned. I expect to be able to obtain metre level global positions for the local survey network points.
Any comments will be appreciated.
|[Prev in Thread]||Current Thread||[Next in Thread]|