NAD83 projection in Texas
My friends and colleagues!... I'm working in San Antonio, Texas, and I have a problem.... I configure my Trimble GPS with NAD83 (2011) projection, working with TxDOT VRS network (Trimble). When I check any Control Point of TxDOT, I have diference about 2 thousand feet... What will happen? The construction project of TxDOT says that reference control point have been measured with VRS TxDOT network in NAD83 (2011) projection... Any Idea?? thank you very much!!
Betcha money the problem is in the difference between Surface and Grid coordinates. About 2200 feet is the difference in the Houston Area.
Do you know what the surface adjustment factor is (from TxDot) for the county you are working in?
edit: or tell me what county you are in and I will look it up.
I'm working close to San Antonio, and the project says that coordinates H&V established from the TxDOT VRS system. distances and coordinates are in US Survey Feet displayed in surface values using a surface adjustment factor of 1.00014. Datum NAD83 2011. I'm working with trimble TSC3. I configure coordinate system with NAD83, but diference of 2000 feet.
thank you very much for the interest!!!
Two points near San Antonio:
Inverse the two points using 680' for the elevations creates a ground/grid scale factor of 1.000163, that means if the SPC is multiplied by the Scale Factor it will increase the Northing by 2220' and the easting by 350'. A lower elevation will decrease that shift.
You need to figure out how the DOT handles ground/grid shifts, if they are multiplying the coordinates by a scale factor that is probably your answer, that is typical DOT procedure and they normally state the SF.
If you are 2000' South South West from the given coordinate that is probably the answer.