ITRF 2014 / GEOID 18

Mark Wheeler

Active Member
I noticed on the OPUS site that they now use ITRF 2014 and GEOID 18. I have been using ITRF 8 and GEOID 12B (Massachusetts). Should I be using the newer options? I do not see GEOID 18 as an option in my selection list.

Mark Wheeler
 

fmhemmer

New Member
We have the same question and would like to be able to select GEOD 18 for DPOS processing. We are also very interested in an explanation of the differences we see in DPOS vs OPUS. Differences are expected because of the different GEOD versions referenced (GEOD 18 vs GEOD 12B). There is an order of magnitude difference in the RMS values and this is of concern to us. Two examples below. Any and all feedback welcomed.

GPD Pt 19091B
DPOS: ORTHO HGT: 1.787(m) 0.003(m) [NAVD88 (Computed using GEOID12B)]
OPUS: ORTHO HGT: 1.801(m) 0.051(m) [NAVD88 (Computed using GEOID18)]

GPS Pt 19091C
DPOS: ORTHO HGT: 2.063(m) 0.004(m) [NAVD88 (Computed using GEOID12B)]
OPUS: ORTHO HGT: 2.046(m) 0.036(m) [NAVD88 (Computed using GEOID18)]
 

fmhemmer

New Member
Regarding the above post, I don't think that the GEOD differences can explain the ortho hght diffrences having much different deltas and the points being within a few hundred feet of each other on relatively flat ground
 

fmhemmer

New Member
We would really like to see answers to these questions as we have the same concerns and would like to get DPOS results in ITRF/GEOID18.
 

Adam

Well-Known Member
5PLS
Geoid 18 is in there now.
So is 2014
EXPLORER-COORDINATE-SYSTEMS_20191030-12.08.44.png
 

Shawn Billings

Shawn Billings
5PLS
I believe the RMS values for orthometric height in OPUS include the error estimates for the geoid. See what the differences in RMS for the ellipsoid heights are. The geoid adds a new variable. I don't think DPOS adds any error estimate for it.
 

Duane Frymire

Active Member
I recieved the following from VT:

"Important NGS News

NGS has recently announced a reprocessing campaign to update the coordinates of CORS stations across the country. This campaign, called the Multi-Year CORS Solution 2 (MYCS2) is aligned to the International Terrestrial Reference Frame (ITRF2014). NGS has also released the new geoid model GEOID18, intended to be the last hybrid geoid model that NGS creates before the current vertical datums are replaced by NAPGD2022.

These updates have potential impacts to the Vermont CORS Network users!

VTrans will be updating/confirming the coordinates of all 18 stations as soon as possible, but we ask that until we announce that stations have been reprocessed with new coordinates, that users DO NOT use GEOID18 in their data collectors to avoid data discrepancy.

We will be keeping users updated with this process and any impacts it may have on the Network."
 
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