[Talk-us-massachusetts] Braintree buildings+(Datum shift)

[Greg Troxel]

Andy Anderson <aanderson at amherst.edu> writes:

> As you note, NAD83 and WGS84 are two different models of the
> Earth. I’ll elaborate from what I know.

Good points, but it's very important to realize that saying "NAD83" or
"WGS84" without specifying which realization is needlessly imprecise.
Basically, the first realization of each were considered equivalent, and
each has become more precise differently and the recent realizations are
not considered equivalent.

Sorry if this is a dup link, but:

  https://www.e-education.psu.edu/geog862/node/1804

> My understanding is that because there is a degree of freedom in
> choosing these, WGS84 was designed to match well in North America.

I have never heard that, and my understanding is that the design aimed
for a global fit.

Yes, NATRF2022 is coming.  I expect that at some point MassGIS will
convert.  I also expect precise transformations to be published.  So
this will not be mysterious, but something we need to be careful about.

As for epcoh of measurement - that's something that OSM has no concept
of now, so it basically remains an error source.  As far as I can tell
GIS in general is not really dealing with that.