Bruce Dawson
Active Member
Very nice Shawn, thanks!
DPOS solution documentation
- Thread starter Sean Joyce
- Start date
Robert P Stenerson
Active Member
I noticed in my DPOS and OPUS reports as it does in the examples in this thread that the reference frame epoch is NAD83 (2011) Epoch 2010. When I created my first NAD83 2011 PA North NAVD88 Reference frame I think I used the default Epoch 2016.xXxX, I.e. I didn't type in 2010. Do I need to create a new standard reference frame with a 2010 Epoch?
Yes. Epoch 2010 is the current standard epoch for NAD83. The differences between 2010 and 2016.xx are likely to be minimal in your area, but there will be a difference. The difference is based on the velocity of your local area according to HTDP modeling (Horizontal Time Dependent Transformation) from NGS. NGS measures the apparent movement of the CORS on the North American Plate and determines regional movement. It's like being on a boat and the boat is moving in the water. The whole boat moves together. This would be the North American Plate. But the boat flexes as it moves through the water. So there is some relative movement too as the hull of the boat slightly torques under the stresses of the wave action. At times it may compress or decompress. These variations would be synonymous with the regional movement observed from the CORS. Epochs allow us to freeze frame this motion and treat the dynamic boat floating at sea with all of its minute relative motion as static. We don't say this IS the coordinate when we measure the point, we actually are saying this WAS the coordinate. NAD83(CONUS) is relatively stable, (excepting the West Coast), so we have some room in our error budget if the epoch is exactly right. But, to be as precise as possible, when using NAD83(2011) use epoch 2010 unless you have good reason not to do so.
Robert P Stenerson
Active Member
Okay, will do, thanks Shawn. For us North Americans your advice might be a good addition to the user guide, page 226, especially for newbies such as myself coming from simpler systems like Carlson SurvCE. I only caught it because of one of Nate's threads with him mentioning entering 2010 for an epoch when using NAD83 (2011). 