Paul,
If you are post processing your data in PathFinder Office you need to export your data using NADCON (transformation parameters are all 0) since the Differential Correction moves your data to State Plane and exporting it to State Plane will do a double shift. Hence the 3 feet, that is the difference (+/-) between WGS84 and NAD83 (2011). Once you export in PathFinder Office you still define your projection as State Plane NAD83 (2011).
Your settings in Terrasync do not effect the raw GPS data. Your GPS data is always stored in WGS84. Terrasync does a projection on the fly to show your data on the Yuma.
Occupy a known point for 180 epochs or so and then use that to estimate what kind of accuracy you may be getting, Trimble reports only precision. You can also use this to gauge if you have exported correctly also try exporting your data with the various definitions of NAD83 and see how it moves.
Stacy DemingGIS ManagerHousatonic Valley AssociationP.O. Box 28
150 Kent Road
Cornwall Bridge, CT 06754
860-662-6678
From: Paul Elsholz <[log in to unmask]>
To: [log in to unmask]
Sent: Tuesday, June 13, 2017 8:10 AM
Subject: [CTGIS-L] GPS accuracy issue
<!--#yiv4626498158 _filtered #yiv4626498158 {font-family:"Cambria Math";panose-1:2 4 5 3 5 4 6 3 2 4;} _filtered #yiv4626498158 {font-family:Calibri;panose-1:2 15 5 2 2 2 4 3 2 4;}#yiv4626498158 #yiv4626498158 p.yiv4626498158MsoNormal, #yiv4626498158 li.yiv4626498158MsoNormal, #yiv4626498158 div.yiv4626498158MsoNormal {margin:0in;margin-bottom:.0001pt;font-size:11.0pt;font-family:"Calibri", sans-serif;}#yiv4626498158 a:link, #yiv4626498158 span.yiv4626498158MsoHyperlink {color:#0563C1;text-decoration:underline;}#yiv4626498158 a:visited, #yiv4626498158 span.yiv4626498158MsoHyperlinkFollowed {color:#954F72;text-decoration:underline;}#yiv4626498158 span.yiv4626498158EmailStyle17 {font-family:"Calibri", sans-serif;color:windowtext;}#yiv4626498158 .yiv4626498158MsoChpDefault {font-family:"Calibri", sans-serif;} _filtered #yiv4626498158 {margin:1.0in 1.0in 1.0in 1.0in;}#yiv4626498158 div.yiv4626498158WordSection1 {}-->Hi— I am the new GIS coordinator at the City of Laconia, NH. I was wondering if someone could shed some light on what’s going on with my GPS data. I have a good system, but I have been disappointed with the accuracy. I use a Trimble Pro XH with a Yuma Tablet. Typically, my uncorrected data yields a horizontal precision of 1.5 to 2 feet. I have been post processing using 3 reference stations: 1) CORS NHDOT CONCORD (NHCO) 2) CORS, U NEW HAMPSHIRE (NHUN) and 3) CORS, BARLETT(BARN) NEW HAMPSHIRE. My corrected data generally has a horizontal precision of 0.5 to 1 foot. When I compare my data points to those taken in the past, or to those on my CAI basemap, I am consistently 2 or 3 feet too far to the north. If this looked like a bell curve in the data, I would write it off as random variation. However, it looks very systematic. Here’s the kicker. My basemap uses NAD 1983 State Plane New Hampshire FIPS 2800 feet. I have experimented collecting/processing my GPS data points using the same datum as my basemap and using ‘96 corrected datum, [NAD 1983 (Conus) CORS 96 State Plane New Hampshire 2800 feet]. When I use the ’96 corrected datum, my GPS points line up with those on the basemap better. I guess that that I am I overlooking something in the datum/projection, but what? Are my expectations for accuracy too high? Should I only use 1 reference station for the differential correction? Is there some hidden setting in Terrasync/Pathfinder that I should check? I thank you ahead of time for your help. Sincerely, Paul Paul Elsholz, GIS Coordinator City of Laconia 27 Bisson Ave. Laconia, NH 03246 Phone: (603) 528-6379 x304 [log in to unmask] -------------------------------------------------------------------------This list (CTGIS-L) is an unmoderated discussion list for all CT GISUsers.If you no longer wish to receive e-mail from this list, you can removeyourself by going to http://listserv.uconn.edu/ctgis-l.html
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