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<p>Our "ground truth" is using WGS84 Ellipsoidal Height. The survey
was created in ~2017, but unfortunately I don't have much
additional info about the Epoch.<br>
<br>
Technically, yes, I am in California - is it fair to say this
complicates things somewhat? The data for conversion is a USGS
survey of the San Francisco Bay Area.<br>
<br>
Following the logic of your process:<br>
<br>
<b>Step 1: Convert the </b><b><i>NAD83(2011) / Conus Albers +
NAVD88 height </i></b><tt><b>to NAD83 Ellipsoidal using
GEOID18 </b><br>
</tt><br>
<br>
E.G.: pdal translate
USGS_LPC_CA_NoCAL_Wildfires_B5b_2018_w2274n1959.laz
Step1_NAD83.laz reprojection
--filters.reprojection.out_srs="+init=EPSG:xxxx
+geoidgrids=~/Downloads/vdatum/core/geoid18/v2018prvi.gtx"
--writers.las.a_srs=EPSG:xxxx<br>
<br>
(Not sure which EPSG codes to use here - any guess?)<br>
<br>
<b>Step 2. Convert resulting Step 1. file into destination
projection (WGS84 UTM 10 Ellipsoidal <a class="moz-txt-link-freetext" href="https://epsg.io/32610">https://epsg.io/32610</a>, or
alternatively, <a class="moz-txt-link-freetext" href="https://epsg.io/7789">https://epsg.io/7789</a> ITRF 2014)<br>
<br>
</b></p>
<div class="moz-cite-prefix">On 7/12/22 14:45, Greg Troxel wrote:<br>
<br>
E.G.: pdal translate
USGS_LPC_CA_NoCAL_Wildfires_B5b_2018_w2274n1959.laz
Step1_NAD83.laz reprojection
--filters.reprojection.out_srs="+init=EPSG:xxxx
+geoidgrids=~/Downloads/vdatum/core/geoid18/v2018prvi.gtx"
--writers.las.a_srs=EPSG:xxxx<br>
<br>
<br>
<br>
<br>
</div>
<blockquote type="cite" cite="mid:rmio7xugg4c.fsf@s1.lexort.com">
<pre class="moz-quote-pre" wrap="">
Nicholas Stanley <a class="moz-txt-link-rfc2396E" href="mailto:nicholas.stanley@luminartech.com"><nicholas.stanley@luminartech.com></a> writes:
</pre>
<blockquote type="cite">
<pre class="moz-quote-pre" wrap="">I am trying to get the /NAD83(2011) / Conus Albers + NAVD88 height/
data *out* of its native elevation model, converted *into* a wgs84
EPSG 32610 ellipsoidal projection.
When I run the conversion command / //pdal translate filename.laz
filename_utm.laz reprojection
--filters.reprojection.out_srs="EPSG:32610"//
/The resulting file lines up in Easting/Northing precisely, but seems
to have retained the old elevation data (which is ~30M+ above our
UTM10 WGS84 "Ground Truth")
</pre>
</blockquote>
<pre class="moz-quote-pre" wrap="">
I would suggest using ITRF2008 or ITRF2014 as a destination, because
WGS84 is an ensemble, and those match the last two membres (and are very
close to each other). In the proj world, NAD83/WGS84 transforms end up
using a null transform, which is arguably pedantically reasonable, but
IMHO in almost all cases the wrong approach.
Strictly, you should be talking about epoch in WGS84(Gnnnn)/ITRFyyyy.
But that's 20-30cm very issh, if you're not in CA.
30M is suspiciously close to a geoid height. So:
You say you have "WGS84" ground truth. Are you clear on whether the
vertical component is "WGS84 Ellipsoidal Height", which is implied by
what you just said, or "WGS84 Orthometric Height"? The two are
related by the EGM2008 gravity model, also published by NGA.
To convert from NAVD88 to WGS84 ellipsoidal height, you have to first
convert to NAD83(2011) ellipsoidal height, using an NGS-published
geoid model such as GEOID18, and then to WGS84/ITRF using a datum
transformation. If you want to go to WGS84 Orthometric Height you
have to do the previous and then apply EGM2008.
FWIW, I have measured NAD83(2011) epoch 2010.0 HAE on a benchmark via
RTK and transformed to NAVD88 and gotten agreement at the 10 cm level.
However this was via looking up GEOID18 on NGS's website and doing it
manually.
I would suggest manually transforming a point to verify your
understanding of what you are dealing with.
</pre>
</blockquote>
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