<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto">Hi,<div>You may be able to remove the geiod height with Gdal but I would use vdatum <a href="https://vdatum.noaa.gov/">https://vdatum.noaa.gov/</a><br><br><div dir="ltr">Nicolas Cadieux<div><a href="https://gitlab.com/njacadieux">https://gitlab.com/njacadieux</a></div></div><div dir="ltr"><br><blockquote type="cite">Le 18 avr. 2021 à 11:17, Raife Crookes <raife@tp-regen.co.uk> a écrit :<br><br></blockquote></div><blockquote type="cite"><div dir="ltr">
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<p class="MsoNormal">Good evening,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I am hoping that someone could assist me with the completion of a reprojection of a geotiff lidar data set to WGS84.
<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">The transformation should me making an elevation change of roughly 50m for known points however after running GDAL warp the elevations are staying the same when viewed through QGIS.
<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">For some reason it seems to be defaulting to the WGS84 geoid height not the ellipsoid height I require for import onto our drone. (My knowledge is that EPSG:4326 should equate to the wgs lat/long and ellipsoid height.)<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">GDALWARP instructions:<o:p></o:p></p>
<p class="MsoNormal">gdalwarp -s_srs EPSG:27700 -t_srs EPSG:4326<o:p></o:p></p>
<p class="MsoNormal">gdalwarp -s_srs -t_srs EPSG:4326<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Proj info return:<o:p></o:p></p>
<p class="MsoNormal">C:\>projinfo -s EPSG:27700 -t EPSG:4326 -o PROJ<o:p></o:p></p>
<p class="MsoNormal">Candidate operations found: 1<o:p></o:p></p>
<p class="MsoNormal">Note: using '--spatial-test intersects' would bring more results (7)<o:p></o:p></p>
<p class="MsoNormal">-------------------------------------<o:p></o:p></p>
<p class="MsoNormal">Operation No. 1:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">unknown id, Inverse of British National Grid + OSGB 1936 to WGS 84 (9), 1 m, UK - Britain and UKCS 49<span style="font-family:"Arial",sans-serif">┬░</span>46'N to 61<span style="font-family:"Arial",sans-serif">┬░</span>01'N, 7<span style="font-family:"Arial",sans-serif">┬░</span>33'W
to 3<span style="font-family:"Arial",sans-serif">┬░</span>33'E<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">PROJ string:<o:p></o:p></p>
<p class="MsoNormal">+proj=pipeline +step +inv +proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717 +x_0=400000 +y_0=-100000 +ellps=airy +step +proj=hgridshift +grids=OSTN15_NTv2_OSGBtoETRS.gsb +step +proj=unitconvert +xy_in=rad +xy_out=deg +step +proj=axisswap
+order=2,1<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I can send copies of the original file if requested. <o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Hoping that its something stupid like im using the wrong EPSG code but have a terrible feeling that a catch all to prevent users accidentally using the ellipsoid height is catching me out.
<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">(Ground height OSGB – 30m in WGS84 = 82m)<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Really look forward to your help/<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Kind regards<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Raife<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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