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Not sure if this helps but here are a few notes.<br>
<br>
GEOID18 supersedes GEOID12B in CONUS and Puerto Rico. GEOID12B
should be used in Alaska, Hawaii, Guam, and the Commonwealth of the
Northern Mariana Islands. American Samoa should not be used for
anything as ASVD02 is no longer valid after earthquakes.<br>
<br>
A note on Geoids, Horizontal (Geometric) Datums and Vertical
Datums. To get an orthometric height (aka elevation) in a
particular vertical datum you should use coordinates in a particular
geometric datum with lat,lon, and ellipsoid height along with a
geoid model to get an orthometric height. For the US here are the
appropriate datums and geoid models. Note that the corresponding
geoid models should be used based on the datum of your coordinates.
Also note the the original NAD 83 (1986) was a 2D datum while all
other realizations were 3D, aka geometric.<br>
<br>
Also note that if you are concerned about accuracy, WGS84 should be
avoided if at all possible. WGS84 has a 3-5 meter uncertainty so
any time you use coordinates or use it as a pivot in transformations
you introduce this uncertainty into your coordinates.<br>
<br>
Table on geoids and NAD 83 realizations<br>
<br>
<table width="551" cellspacing="0" cellpadding="0" border="0">
<colgroup><col
style="mso-width-source:userset;mso-width-alt:7168;width:147pt"
width="196"> <col
style="mso-width-source:userset;mso-width-alt:5156;width:106pt"
width="141"> <col style="width:161pt" width="214"> </colgroup><tbody>
<tr style="height:15.75pt" height="21">
<td class="xl66" dir="LTR" style="height:15.75pt;width:147pt"
width="196" height="21">NAD 83 (realization)</td>
<td class="xl66" dir="LTR"
style="border-left:none;width:106pt" width="141">Geoid Model</td>
<td class="xl68" dir="LTR"
style="border-left:none;width:161pt" width="214">Regions</td>
</tr>
<tr style="height:15.75pt" height="21">
<td class="xl67" dir="LTR" style="height:15.75pt;border-top:
none;width:147pt" width="196" height="21">NAD 83 (1986)</td>
<td class="xl67" dir="LTR"
style="border-top:none;border-left:none; width:106pt"
width="141">N/A</td>
<td class="xl68" dir="LTR"
style="border-top:none;border-left:none"> </td>
</tr>
<tr style="height:15.75pt" height="21">
<td class="xl67" dir="LTR" style="height:15.75pt;border-top:
none;width:147pt" width="196" height="21">NAD 83 (HARN)</td>
<td class="xl67" dir="LTR"
style="border-top:none;border-left:none; width:106pt"
width="141">GEOID96/GEOID99</td>
<td class="xl68" dir="LTR"
style="border-top:none;border-left:none"> </td>
</tr>
<tr style="height:15.75pt" height="21">
<td class="xl67" dir="LTR" style="height:15.75pt;border-top:
none;width:147pt" width="196" height="21">NAD 83 (FBN)</td>
<td class="xl67" dir="LTR"
style="border-top:none;border-left:none; width:106pt"
width="141">GEOID03</td>
<td class="xl68" dir="LTR"
style="border-top:none;border-left:none"> </td>
</tr>
<tr style="height:15.75pt" height="21">
<td class="xl67" dir="LTR" style="height:15.75pt;border-top:
none;width:147pt" width="196" height="21">NAD 83 (CORS96)</td>
<td class="xl67" dir="LTR"
style="border-top:none;border-left:none; width:106pt"
width="141">GEOID03</td>
<td class="xl68" dir="LTR"
style="border-top:none;border-left:none"> </td>
</tr>
<tr style="height:15.75pt" height="21">
<td class="xl67" dir="LTR" style="height:15.75pt;border-top:
none;width:147pt" width="196" height="21">NAD 83 (NSRS2007)</td>
<td class="xl67" dir="LTR"
style="border-top:none;border-left:none; width:106pt"
width="141">GEOID09</td>
<td class="xl68" dir="LTR"
style="border-top:none;border-left:none"> </td>
</tr>
<tr style="height:15.75pt" height="21">
<td class="xl67" dir="LTR" style="height:15.75pt;border-top:
none;width:147pt" width="196" height="21">NAD 83 (2011)</td>
<td class="xl67" dir="LTR"
style="border-top:none;border-left:none; width:106pt"
width="141">GEOID12B</td>
<td class="xl68" dir="LTR"
style="border-top:none;border-left:none">HI, AK, Guam, CNMI</td>
</tr>
<tr style="height:15.75pt" height="21">
<td class="xl67" dir="LTR" style="height:15.75pt;border-top:
none;width:147pt" width="196" height="21">NAD 83 (2011)</td>
<td class="xl67" dir="LTR"
style="border-top:none;border-left:none; width:106pt"
width="141">GEOID18</td>
<td class="xl68" dir="LTR"
style="border-top:none;border-left:none">CONUS, PRVI</td>
</tr>
</tbody>
</table>
<br>
Cheers<br>
Brian<br>
<br>
<br>
<div class="moz-cite-prefix">On 11/1/2019 4:33 PM, Even Rouault
wrote:<br>
</div>
<blockquote type="cite" cite="mid:5925847.I67IV3XJ70@even-i700">
<pre class="moz-quote-pre" wrap="">On vendredi 1 novembre 2019 13:12:11 CET YK_climate wrote:
</pre>
<blockquote type="cite">
<pre class="moz-quote-pre" wrap="">Hello,
I have been trying to perform vertical transformation with Proj for a few
days now, I think I am done but I am in some help to be sure I didn't make
some stupid mistakes!
I am looking at getting coordinates in WGS84-Ellipsoid to WG84-EGM96,WG84-
EGM2008 and to NAD83(2011)GEOID12B.
Here is what I have working so far :
WGS84-EGM2008 : cs2cs EPSG:4979 EPSG:4326+3855
WGS84-EGM96 : cs2cs EPSG:4979 EPSG:4326+5773
Is this correct?
</pre>
</blockquote>
<pre class="moz-quote-pre" wrap="">
Yes
</pre>
<blockquote type="cite">
<pre class="moz-quote-pre" wrap="">
So naturally I thought that GEOID12B would be as easy :
NAD83(2011)-GEOID12B : cs2cs EPSG:4979 EPSG:6319+5703 <= no vertical
change
NAD83(2011)-GEOID12B : cs2cs EPSG:4979 EPSG:5498 <= no vertical
change
</pre>
</blockquote>
<pre class="moz-quote-pre" wrap="">
As the target SRS here use the NAVD88 height vertical CRS, but in EPSG, there
is no transformation from NAVD88 to WGS84, then PROJ < 6.2.1 didn't do any
vertical change.
Starting with PROJ 6.2.1, it will use the NAVD88->NAD83/NAD83(2011) grids, so
GEOID12B if that's what you've available, as a fallback.
$ ~/proj/install-proj-6.2.1/bin/projinfo -s EPSG:4979 -t EPSG:5498 --spatial-
test intersects
Candidate operations found: 294
-------------------------------------
Operation n°1:
unknown id, NAD83(2011) to NAVD88 height (1) + Inverse of NAD83 to WGS 84 (1),
4.02 m, USA - CONUS - onshore, at least one grid missing
PROJ string:
+proj=pipeline +step +proj=axisswap +order=2,1 +step +proj=unitconvert
+xy_in=deg +xy_out=rad +step +inv +proj=vgridshift +grids=g2012bu0.gtx
+multiplier=1 +step +proj=unitconvert +xy_in=rad +xy_out=deg +step
+proj=axisswap +order=2,1
Even
</pre>
</blockquote>
<br>
<pre class="moz-signature" cols="72">--
*************************************
Brian Shaw
Geodesist
NOAA/NOS/National Geodetic Survey
Phone # 240-533-9522</pre>
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