I suggest to treat it as a separate datum, the coordinates would be different although the differences are for most applications negligible.
With the sub-meter resolution data now quite common it is important to treat it as different.
See more info here:
http://www2.arnes.si/~gljsentvid10/datm_faq.html#1.2
https://confluence.qps.nl/pages/viewpage.action?pageId=29855153
http://www.ngs.noaa.gov/faq.shtml#WhatHARN
Just to make things more complicated a committee was set up in NC to decide how to deal with upcoming dynamic datum with more frequent updates.
Helena
···
On Mon, Apr 25, 2016 at 10:47 PM, Markus Neteler <neteler@osgeo.org> wrote:
(cc Helena)
First of all, thanks to Even and Paul to shed some light on this!
On Mon, Apr 25, 2016 at 10:37 PM, Paul Kelly
<paul-grass@stjohnspoint.co.uk> wrote:
…The problem is actually even simpler (datum simply not recognised in GRASS)
and there are two possible solutions:
If we want NAD83_High_Accuracy_Reference_Network to be treated as a
completely separate datum from North_American_Datum_1983, then we add it as
a new line in lib/gis/datum.table as per the first attached patch.If we want NAD83_High_Accuracy_Reference_Network to be treated as
equivalent to North_American_Datum_1983 (this means once the location has
been created, ‘g.proj -w’ will report the datum name as
North_American_Datum_1983), then we add two new lines to the equivalent
pairs array in lib/proj/convert.c as per the second attached patch.I don’t really feel qualified to decide which is the most desirable
behaviour, so I’ll leave that up to someone else to decide, if that’s OK.I also don’t feel too qualified here
but from a user’s point of
view a change of name is confusing.So option 1) looks better to me (i.e., " datum.table.patch") which is
tested ok here.
Maybe Helena as our NC expert has an opinion here?Paul, still struggling with “SIRGAS2000”
https://trac.osgeo.org/grass/ticket/2456#comment:15
(g.proj versus testepsg output). Needs a different trick?Markus
–
Markus Neteler
http://www.mundialis.de - free data with free software
http://courses.neteler.org/blog/
–
Helena Mitasova
Professor
Department of Marine, Earth and Atmospheric Sciences
North Carolina State University
1125 Jordan Hall
NCSU Box 8208
Raleigh, NC 27695-8208
http://www4.ncsu.edu/~hmitaso/
http://geospatial.ncsu.edu/
email: hmitaso@ncsu.edu
ph: 919-513-1327 (no voicemail)
fax 919 515-7802