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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">Thomas,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">I’m open to correction on this, but meters would generally be the default unit used in GIS, when dealing with metric datasets.
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">What units you use to measure on your Map Canvas or store as attribution is then a different thing.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">I had a look for the EPSG codes for EASE2 but all I could get was
<b><a href="https://epsg.io/6931">EPSG:6931</a></b><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">If you look at the units there you can see meters as the UoM.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">I hope that helps,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">Richard.<o:p></o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">From:</span></b><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif"> QGIS-User <qgis-user-bounces@lists.osgeo.org>
<b>On Behalf Of </b>Thomas Lavergne via QGIS-User<br>
<b>Sent:</b> 15 September 2023 13:34<br>
<b>To:</b> qgis-user@lists.osgeo.org<br>
<b>Subject:</b> [Qgis-user] Does QGIS require units "m" for the projection coordinate variables in a netCDF/CF file?<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Dear QGIS community,<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">We recently released a number of sea-ice climate data records stored in netCDF/CF files.<o:p></o:p></p>
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<p class="MsoNormal">An example file is <a href="https://thredds.met.no/thredds/catalog/osisaf/met.no/reprocessed/ice/drift_455m_files/merged/2020/12/catalog.html?dataset=osisaf/met.no/reprocessed/ice/drift_455m_files/merged/2020/12/ice_drift_nh_ease2-750_cdr-v1p0_24h-202012211200.nc" target="_blank">here</a>:<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Our files use a polar equal area projection (EASE2) and the x / y axis values are given with units "km" (kilometers):<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">double xc(xc) ;<br>
xc:axis = "X" ;<br>
xc:units = "km" ;<br>
xc:long_name = "x coordinate of projection (eastings)" ;<br>
xc:standard_name = "projection_x_coordinate" ;<br>
double yc(yc) ;<br>
yc:axis = "Y" ;<br>
yc:units = "km" ;<br>
yc:long_name = "y coordinate of projection (northings)" ;<br>
yc:standard_name = "projection_y_coordinate" <o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">When opening these in QGIS, they are placed correctly on the map, but the message "Unkown CRS" appears in the lower-right corner.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">By manipulating our files, we could get QGIS to recognize the correct CRS.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">ncap2 -s 'xc=xc*1000f;yc=yc*1000f' <a href="http://infile.nc/" target="_blank">infile.nc</a> <a href="http://outfile.nc/" target="_blank">outfile.nc</a><br>
ncatted -O -a units,xc,m,c,"m" <a href="http://outfile.nc/" target="_blank">outfile.nc</a><br>
ncatted -O -a units,yc,m,c,"m" <a href="http://outfile.nc/" target="_blank">outfile.nc</a><br clear="all">
<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">The NCO commands above change the x / y axis variables to units "m" (meters).<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">The <a href="http://cfconventions.org/Data/cf-conventions/cf-conventions-1.10/cf-conventions.html" target="_blank">CF convention</a> does not impose that x / y axis variables are given with unit meters, and shows several examples using
units "km". But this is apparently an issue for QGIS.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Can someone please confirm that QGIS requires "meters" for these variables, and comment if this is a desired feature or if I should open a bug report at github?<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">All the best,<o:p></o:p></p>
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<p class="MsoNormal">Thomas<o:p></o:p></p>
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