<div dir="ltr">I'm sure others with more experience will jump in, but I think the main issue here is that WGS84 is a family of reference frames that are all based on the GRS80 ellipsoid. So, the problem doesn't exactly make sense and the various realizations of WGS84 differ at the cm level. Are you perhaps trying to go from a NAD83 realization (such as NAD83(2011)) to a WGS84 realization (maybe ITRF14 <div>or something)?</div><div><br clear="all"><div><div dir="ltr" class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div><font face="arial, helvetica, sans-serif">Kirk Waters, PhD </font></div><div><font face="arial, helvetica, sans-serif">NOAA Office for Coastal Management<br></font></div><div><font face="arial, helvetica, sans-serif">Applied Sciences Program </font></div><div>Phone: 843-284-6962 (New as of 2022) <font face="arial, helvetica, sans-serif"> </font><div><font face="arial, helvetica, sans-serif"><a href="http://coast.noaa.gov/digitalcoast" target="_blank">coast.noaa.gov/digitalcoast</a></font><br></div></div><div><br><br></div></div></div></div></div></div></div></div></div><br></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Wed, Jan 19, 2022 at 3:55 PM Joseph Boardman <<a href="mailto:boardman@aigllc.com">boardman@aigllc.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
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<th valign="BASELINE" nowrap align="RIGHT">Subject:
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<td>some help with cm-level GRS80 to WGS-84 transformation?</td>
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<th valign="BASELINE" nowrap align="RIGHT">Date: </th>
<td>Wed, 19 Jan 2022 11:28:24 -0700</td>
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<th valign="BASELINE" nowrap align="RIGHT">From: </th>
<td>Joseph Boardman <a href="mailto:boardman@aigllc.com" target="_blank"><boardman@aigllc.com></a></td>
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<td><a href="mailto:proj@lists.osgeo.org" target="_blank">proj@lists.osgeo.org</a></td>
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<p>Dear Proj Experts,</p>
<p>I'm a remote sensing geophysicist with experience in geodesy
and mapping.</p>
<p>Right now I'm struggling trying to get a high-accuracy proj
command to convert from GRS80 to WGS-84 at the cm level.</p>
<p>Any clues? cs2cs is not doing it.<br>
</p>
<p><span style="color:rgb(29,28,29);font-family:Slack-Lato,appleLogo,sans-serif;font-size:15px;font-style:normal;font-variant-ligatures:common-ligatures;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:left;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">cs2cs
+proj=lonlat +ellps=WGS84 +to +proj=lonlat +ellps=GRS80 -d 8</span><br style="box-sizing:inherit;color:rgb(29,28,29);font-family:Slack-Lato,appleLogo,sans-serif;font-size:15px;font-style:normal;font-variant-ligatures:common-ligatures;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:left;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial">
<span style="color:rgb(29,28,29);font-family:Slack-Lato,appleLogo,sans-serif;font-size:15px;font-style:normal;font-variant-ligatures:common-ligatures;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:left;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">-120 40</span><br style="box-sizing:inherit;color:rgb(29,28,29);font-family:Slack-Lato,appleLogo,sans-serif;font-size:15px;font-style:normal;font-variant-ligatures:common-ligatures;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:left;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial">
<span style="color:rgb(29,28,29);font-family:Slack-Lato,appleLogo,sans-serif;font-size:15px;font-style:normal;font-variant-ligatures:common-ligatures;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:left;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">-120.00000000
40.00000000 0.00000000</span></p>
<p>Do I need to do a transformation pipeline per the 8.2.1 docs
and use a Helmert transform? Any help much appreciated.</p>
<p>Best,</p>
<p>Joe</p>
<p><br>
<span style="color:rgb(29,28,29);font-size:15px;font-style:normal;font-variant-ligatures:common-ligatures;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:left;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"></span><span style="color:rgb(29,28,29);font-family:Slack-Lato,appleLogo,sans-serif;font-size:15px;font-style:normal;font-variant-ligatures:common-ligatures;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:left;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"></span></p>
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