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What epoch is GCS_WGS_1984 in 10.4?

Question asked by joeb@cwd on Mar 30, 2016
Latest reply on Mar 3, 2017 by MKennedy-esristaff

What epoch does ArcMap 10.4 reference when you choose GCS_WGS_1984 as the datum?
Is it the current epoch of 2005.0 equivalent with ITRF08, or the previous epoch
of 1997.0 equivalent with ITRF00?

 

I am finding that much of the reference material online is outdated
as it lists the current realization of WGS84 to be equivalent to
ITRF00, Epoch 1997.0. This article by NGS (http://www.ngs.noaa.gov/CORS/Articles/SolerWGS84(G1674)-to-NAD83(2011).pdf)
explains that GPS satellites actually report their X,Y & Z location values
in IGS08, which is also equivalent to WGS84(G1674)/ITRF08. However, the epoch
of the recorded points is the time they were transmitted from the satellites;
they need to be reduced to a common epoch before they can be compared with
other coordinates (because of tectonic movement). The article also mentions
your “software” may already do this for you. I am collecting points with
Trimble Geo6000 receivers; I don’t know if the TerraSync software does this
during collections or if the Pathfinder Office software does this during post
processing. And if it does, I don’t know what the epoch it uses for WGS1984 is.
I suspect it is epoch 1997.0 as the base station reference positions are listed
in ITRF00.

Once I figure out the correct conversion process from GPS points in Trimble’s
TerraSync to our NAD1983(epoch 1986) GIS, I will need to revisit this for using
the Collector App or possibly the Trimble Positions plug-in: Where is the epoch
conversion made and what is that epoch?

 

Thanks.

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