Hello fellow surveyors,
I wanted to run this by you to see if I am on the right track.
I submitted RINEX data to OPUS and was reviewing my results. I believe NAD83(2011)EPOCH2010.0 is based off the ITRF2014. I figure the degree seconds are off a little because the results are displayed in the current EPOCH of the ITRF and the computed NAD83 coordinates are referenced to the 2010.00 EPOCH which is in the past.
Let me know if I am thinking through this correctly.
Thanks,
Dan
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It's partly affected by epoch, but mostly by where the datum is centered.?ÿ NAD83(xxxx) has stuck with the original definition, but ITRF uses an updated center of earth. NGS toolkit has a translation tool to deal with it, and that is used in generating the OPUS report.
This appears to be your February submission on rivet RV 9.?ÿ It's a good thing you did it when the leaves were off.?ÿ That's a subject of much interest to me because of a recent attempt that had limbs closer than that (thread).
OPUS does compute in ITRF current epoch, then uses HTDP to convert to NAD83 (2011) epoch 2010.0. The difference is somewhere around 1.6 meters 3D, 1.3 m horizontal for your point.?ÿ
As far as whether the NAD83 (2011) epoch 2010.0 is a bit off due to age, it depends on where you are. I don't believe you should see any significant drift in the middle of Iowa.?ÿ
NAD83 and ITRF are based on quite separate ellipsoids. NAD is used in North America, ITRF is used elsewhere.?ÿ?ÿ
The original poster??s guess that the difference in coordinates is (solely) due to velocities is incorrect.
As Mr Hamilton writes, OPUS solutions are computed in ITRF (now 2014) and transformed by a set of 14-parameters to NAD83(2011) reference epoch 2010.0 I extracted from the HTDP source code the transformation parameters used for ITRF2014->ITRF94 then ITRF94->NAD83.
Norman Oklahoma is incorrect in his statement that NAD83 and the various implementations of ITRF use difference reference ellipsoids. Both use GRS80. The reference ellipsoid is only involved when transforming from Cartesian XYZ to geodetic lat, Lon, ellipsoid height.
I took the coordinates in the OP and ran them through HTDP on the NGS site. Note the annotations showing the subtracted differences in coordinates and the yearly velocities.?ÿ
The 14-parameters are 3 translations, 3 rotations, a scale difference and the time-varying magnitudes of the seven.
I show screen captures below:
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Norman Oklahoma is incorrect ...
I accept your verdict, waive the right of appeal, and sentence myself to several evenings of further study.
Also important to note that the International Earth Rotation and Reference System Service (IERS) who produce the ITRF show coordinates almost exclusively as X,Y,Z Earth-Centered Earth-Fixed values and only rarely as latitude, longitude and ellipsoid height - they leave that up to the user to define the ellipsoid of reference.