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</o:shapelayout></xml><![endif]--></head><body lang=PT link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'>The IMG grids are spherical Mercator inches so there is likely no EPSG or WKT that represents that. But you can do all the work in GMT.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'>1- Convert to netcdf, maintaining the Merc projection, but change the origin to (0,0) (it was in the LL corner). That’s the role of -C<o:p></o:p></span></p><p class=MsoListParagraph><span lang=EN-US style='mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal style='margin-left:.25in'><span lang=EN-US style='mso-fareast-language:EN-US'>img2grd -R-180/180/-80/80 topo_19.1.img -Gspherical-mercator-proj.grd -T1 -D -M -C<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'>2- Edit the header to convert the inches to Mercator meters. The grid above has x_min = -180; x_max = 180.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'>And that corresponds to 6378137 *2pi = 4.007501668557849e7 meters. So we can compute a scale factor of <o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'>111319.49079327358 = 6378137 *2pi / 360<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'>and apply it to the region in degrees.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'>[-180 180 -139.6 139.6] .* 111319.49079327358 = -20037508.3427892 20037508.3427892 -15540200.914741 15540200.914741<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'>So finaly use grdedit to change the limits and assign it a proj4 string describing the projection<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'>grdedit spherical-mercator-proj.grd -R-20037508.3427892/20037508.3427892/-15540200.914741/15540200.914741 -J"+proj=merc +lon_0=0 +k=1 +x_0=0 +y_0=0 +a=6378137 +b=6378137 +units=m +no_defs"<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'>You can now confirm with gdalinfo<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'>C:\v>gdalinfo spherical-mercator-proj.grd<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'>Warning 1: dimension #1 (x) is not a Longitude/X dimension.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'>Warning 1: dimension #0 (y) is not a Latitude/Y dimension.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'>Driver: netCDF/Network Common Data Format<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'>Files: spherical-mercator-proj.grd<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'>Size is 21600, 16752<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'>Coordinate System is:<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'>PROJCS["unnamed",<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'> GEOGCS["unnamed ellipse",<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'> DATUM["unknown",<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'> SPHEROID["unnamed",6378137,0]],<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'> PRIMEM["Greenwich",0],<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'> UNIT["degree",0.0174532925199433]],<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'> PROJECTION["Mercator_1SP"],<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'> PARAMETER["central_meridian",0],<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'> PARAMETER["scale_factor",1],<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'> PARAMETER["false_easting",0],<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'> PARAMETER["false_northing",0],<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'> UNIT["Meter",1]]<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'>Origin = (-20037148.342789199000000,15540200.914741000000000)<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'>Pixel Size = (1855.324846554555500,-1855.324846554560700)<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'>Metadata:<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'> grid_mapping#spatial_ref=PROJCS["unnamed",<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'> GEOGCS["unnamed ellipse",<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'> DATUM["unknown",<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'> SPHEROID["unnamed",6378137,0]],<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'> PRIMEM["Greenwich",0],<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'> UNIT["degree",0.0174532925199433]],<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'> PROJECTION["Mercator_1SP"],<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'> PARAMETER["central_meridian",0],<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'> PARAMETER["scale_factor",1],<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'> PARAMETER["false_easting",0],<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'> PARAMETER["false_northing",0],<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'> UNIT["Meter",1]]<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'> NC_GLOBAL#Conventions=CF-1.7<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'> NC_GLOBAL#description=Spherical Mercator Projected with -Jm1 -R-180/180/-80.0023237126/80.0023237126<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'> NC_GLOBAL#GMT_version=6.0.0_bcb87fa-dirty_2019.05.07 [64-bit] [MP]<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'> NC_GLOBAL#history=img2grd -R-180/180/-80/80 topo_19.1.img -Gspherical-mercator-proj.grd -T1 -D -M -C<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'> NC_GLOBAL#node_offset=1<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'> NC_GLOBAL#title=Data from Altimetry<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'> x#actual_range={-20037148.3427892,20037868.3427892}<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'> x#long_name=x_units<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'> y#actual_range={-15540200.914741,15540200.914741}<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'> y#long_name=y_units<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'> z#actual_range={-10914,8550}<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'> z#grid_mapping=grid_mapping<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'> z#long_name=meters, mGal, Eotvos, micro-radians or Myr, depending on img file and -S.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'> z#_FillValue=-1.#IND<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'>Corner Coordinates:<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'>Upper Left (-20037148.343,15540200.915) (179d59'48.36"W, 80d 0' 8.37"N)<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'>Lower Left (-20037148.343,-15540200.915) (179d59'48.36"W, 80d 0' 8.37"S)<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'>Upper Right (20037868.343,15540200.915) (179d59'48.36"W, 80d 0' 8.37"N)<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'>Lower Right (20037868.343,-15540200.915) (179d59'48.36"W, 80d 0' 8.37"S)<o:p></o:p></span></p><p class=MsoNormal><span style='mso-fareast-language:EN-US'>Center ( 360.000, 0.000) ( 0d 0'11.64"E, 0d 0' 0.01"N)<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'>Band 1 Block=21600x1 Type=Float32, ColorInterp=Undefined<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'> NoData Value=nan<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'> Metadata:<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'> actual_range={-10914,8550}<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'> grid_mapping=grid_mapping<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'> long_name=meters, mGal, Eotvos, micro-radians or Myr, depending on img file and -S.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'> NETCDF_VARNAME=z<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'> _FillValue=-1.#IND<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'>Joaquim<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'>(with Paul’s help for the scaling factor)<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:EN-US'><o:p> </o:p></span></p><div style='border:none;border-left:solid blue 1.5pt;padding:0in 0in 0in 4.0pt'><div><div style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in'><p class=MsoNormal><b><span lang=EN-US>From:</span></b><span lang=EN-US> PROJ <proj-bounces@lists.osgeo.org> <b>On Behalf Of </b>Kurt Schwehr<br><b>Sent:</b> Tuesday, May 7, 2019 10:52 PM<br><b>To:</b> PROJ <proj@lists.osgeo.org><br><b>Subject:</b> [PROJ] Projection for Sandwell et al.'s topex topo and grav files?<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><div><div><div><div><div><p class=MsoNormal>Hi all,<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>I figured I should ask here too if anyone know what the correct projection is for the Sandwell .img grids from <a href="http://topex.ucsd.edu">http://topex.ucsd.edu</a>. I'm trying to keep the files in their original projections as I switch them to geotiffs. I've asked David Sandwell directly too if he knows.<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>This works, but warps the data first:<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><div><p class=MsoNormal>gmt img2grd -V -R-180/180/-80/80 topo_18.1.img -Gtest2.grd -T1 -D<o:p></o:p></p></div><div><p class=MsoNormal>gdal_translate -a_srs EPSG:4326 test2.grd test2.tif<o:p></o:p></p></div><div><p class=MsoNormal>gdalinfo test2.tif # Results look believable<o:p></o:p></p></div><div><p class=MsoNormal>gdal_translate topo-18-1-epsg4326.tif topo-18-1-epsg4326-deflate.tif -co COMPRESS=DEFLATE -co PREDICTOR=3<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>Then imported into QGIS or Earth Engine as a normal user, things line up pretty well.<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal> <a href="https://code.earthengine.google.com/f43c8b13bafa26fd8c7f83ce9a919f6e">https://code.earthengine.google.com/f43c8b13bafa26fd8c7f83ce9a919f6e</a><o:p></o:p></p></div></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>I'd rather do it more like this:<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><div><p class=MsoNormal>gmt img2grd -V -R-180/180/-80/80 topo_18.1.img -Gspherical-mercator-proj.grd -T1 -D -M<o:p></o:p></p></div><div><p class=MsoNormal>img2grd: Expects topo_18.1.img to be 21600 by 17280 pixels spanning 0/360.0/-80.738009/80.738009.<o:p></o:p></p></div><div><p class=MsoNormal>img2grd: To fit [averaged] input, your topo_18.1.img is adjusted to -R-180/180/-80.0023237126/80.0023237126.<o:p></o:p></p></div><div><p class=MsoNormal>img2grd: The output grid size will be 21600 by 16752 pixels.<o:p></o:p></p></div><div><p class=MsoNormal>img2grd: Created 21600 by 16752 Mercatorized grid file. Min, Max values are -10914 8550<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>gives this which doesn't work as is:<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>gdalinfo spherical-mercator-proj.grd<o:p></o:p></p></div><div><p class=MsoNormal>Driver: netCDF/Network Common Data Format<o:p></o:p></p></div><div><p class=MsoNormal>Files: spherical-mercator-proj.grd<o:p></o:p></p></div><div><p class=MsoNormal>Size is 21600, 16752<o:p></o:p></p></div><div><p class=MsoNormal>Coordinate System is `'<o:p></o:p></p></div><div><p class=MsoNormal>Origin = (0.000000000000000,279.199999999999989)<o:p></o:p></p></div><div><p class=MsoNormal>Pixel Size = (0.016666666666667,-0.016666666666667)<o:p></o:p></p></div><div><p class=MsoNormal>Metadata:<o:p></o:p></p></div><div><p class=MsoNormal> NC_GLOBAL#Conventions=COARDS, CF-1.5<o:p></o:p></p></div><div><p class=MsoNormal> NC_GLOBAL#description=Spherical Mercator Projected with -Jm1 -R0/360/-80.0023237126/80.0023237126<o:p></o:p></p></div><div><p class=MsoNormal> NC_GLOBAL#GMT_version=5.4.3 (r19528) [64-bit]<o:p></o:p></p></div></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>Should I be using one of 54004 or 41001? e.g. <a href="https://epsg.io/?q=spherical+mercator">https://epsg.io/?q=spherical+mercator</a><o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>Thanks!<o:p></o:p></p></div><div><p class=MsoNormal>-kurt<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div></div></div></div></div></div></div></body></html>