On Wed, Jun 28, 2017 at 4:02 PM, preiaen <[email protected]> wrote: > > Dear Markus, > > thank you for your answer. I did as you suggested and below are the results. > As far as I can understand it, it looks fine, however the error remains. > > *For the shapefile: * > > *g.proj -g:* > > -PROJ_INFO------------------------------------------------- > name : WGS 84 / Pseudo-Mercator > datum : wgs84 > ellps : wgs84 > proj : merc > lat_ts : 0.0 > lon_0 : 0.0 > x_0 : 0.0 > y_0 : 0 > k : 1.0 > wktext : defined > no_defs : defined > -PROJ_EPSG------------------------------------------------- > epsg : 3857 > -PROJ_UNITS------------------------------------------------ > unit : meter > units : meters > meters : 1 > > *ogrinfo:* > > PROJCS["WGS 84 / Pseudo-Mercator", > GEOGCS["WGS 84", > DATUM["WGS_1984", > SPHEROID["WGS 84",6378137,298.257223563, > AUTHORITY["EPSG","7030"]], > AUTHORITY["EPSG","6326"]], > PRIMEM["Greenwich",0, > AUTHORITY["EPSG","8901"]], > UNIT["degree",0.0174532925199433, > AUTHORITY["EPSG","9122"]], > 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"]], > AXIS["X",EAST], > AXIS["Y",NORTH],
So far, all looks fine, but > EXTENSION["PROJ4","+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 > +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +wktext > +no_defs"], a (equatorial radius) and b (polar radius) are the same, i.e. this is a sphere, not an ellipsoid like wgs84. This can make a difference. You can try to use the proj4 term +proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs to create a new location, then force import the shapefile with v.in.ogr -o, then reproject and check if it is the geolocation is correct. > AUTHORITY["EPSG","3857"]] See http://epsg.io/3857 "Remarks: Uses spherical development of ellipsoidal coordinates. Relative to WGS 84 / World Mercator (CRS code 3395) errors of 0.7 percent in scale and differences in northing of up to 43km in the map (equivalent to 21km on the ground) may arise." Markus M > > *For the DEM:* > > g.proj -p > -PROJ_INFO------------------------------------------------- > name : WGS 84 > datum : wgs84 > ellps : wgs84 > proj : ll > no_defs : defined > -PROJ_UNITS------------------------------------------------ > unit : degree > units : degrees > meters : 1.0 > > *gdalinfo:* > > 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"]] > > > Nils > > > > -- > View this message in context: http://osgeo-org.1560.x6.nabble.com/Projection-errors-with-Aster-GDEM-and-SHP-Files-tp5324655p5325865.html > Sent from the Grass - Users mailing list archive at Nabble.com. > _______________________________________________ > grass-user mailing list > [email protected] > https://lists.osgeo.org/mailman/listinfo/grass-user
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