Le mardi 17 novembre 2015 17:55:15, Jonathan Moules a écrit : > Hi List, > I have a Geotiff which includes this projection: > > PROJ.4 : '+proj=merc +lon_0=0 +k=1 +x_0=0 +y_0=0 +datum=WGS84 +units=m > +no_defs ' > > > OGC WKT : > PROJCS["Mercator", > GEOGCS["WGS 84", > DATUM["WGS_1984", > SPHEROID["WGS 84",6378137,298.257223563, > AUTHORITY["EPSG","7030"]], > AUTHORITY["EPSG","6326"]], > PRIMEM["Greenwich",0], > UNIT["degree",0.0174532925199433], > AUTHORITY["EPSG","4326"]], > PROJECTION["Mercator_1SP"], > PARAMETER["central_meridian",0], > PARAMETER["scale_factor",1], > PARAMETER["false_easting",0], > PARAMETER["false_northing",0], > UNIT["metre",1, > AUTHORITY["EPSG","9001"]]] > > > > > If I load this raster into ArcGIS, it displays in the wrong place (a few > thousand kilometres North). > > > I then run it through gdal_translate (GDAL 1.11.1), with no flags: > * gdal_trainslate input.tif output.tif > > For output.tif, GDALSRSInfo shows that the projection is identical, but now > the file loads correctly in ArcGIS. The same file works fine in QGIS both > before and after the "translation". > > > Looking at the projection info in ArcGIS, it displays one difference: > Before (not working): > Standard_parallel_1 = 60 > > > After (working): > Standard_parallel_1 = 0 > > > But I don't see anything about those in either of the GDALSRSInfo outputs. > > > So my questions: > - What is gdal_translate doing to the file to "fix" it? > - If it is something to do with Standard Parallel 1 - why isn't this > component of the projection exposed by GDAL?
Yes, in Mercator_1SP, there's no Standard Parallel 1, this is for Mercator_2SP. See http://www.remotesensing.org/geotiff/proj_list/mercator_1sp.html http://www.remotesensing.org/geotiff/proj_list/mercator_2sp.html I guess your original geotiff file has some unusual formulation which is detected as Mercator_1SP by GDAL, and probably Mercator_2SP by ArCGIS. You could try with the listgeo utility that comes with libgeotiff to display the geotiff keys. > > Thoughts welcome. > Thanks, > Jonathan -- Spatialys - Geospatial professional services http://www.spatialys.com _______________________________________________ gdal-dev mailing list gdal-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/gdal-dev
