Re: [GRASS-user] DAtum Warning while using r.in.gdal
Thanks to Paul and Micha for the help. About this: I defined my location using this image but instead of being reprojected with PROJ4 extension I used EPSG:3763 and then r.in.gdal. Then, using the same original image (in UTM) I reprojected to this CRS but using PROj4 extension (showed in my original message). What is the correct one? the bellow expression or the EPSG:3763 in order to reproject an image? It was only a warning. It imported the image nevertheless, without using -o option. 2010/5/31 Micha Silver mi...@arava.co.il On 05/31/2010 07:25 PM, Kim Besson wrote: Greetings Following a few suggestions made at this list I'm using gdalwarp to project a few landsat images and only then yusing r.in.gdal. I'm using this expression to reproject image: gdalwarp -t_srs +proj=tmerc +lat_0=39.668258 +lon_0=-8.1331084 +k=1 +x_0=0 +y_0=0 +ellps=GRS80 +units=m +no_defs L71203033_03320001023_B10.TIF landsat_out.tif And when I run r.in.gdal I get this warning: Datum unknown not recognised by GRASS and no parameters found Projection of input dataset and current location appear to match What does this means? There's no +datum= parameter in the CRS definition, so the new, projected tif has no datum information. But, if you're sure the above parameters are correct, you can ignore the warning and tell GRASS to ignore the warning with the -o option to r.in.gdal. BTW, how did you define the GRASS Location? with the EPSG:3763 or the above definition? If so, then you surely should have no problem importing with the -o (over-ride projection check) option. Thanks kim This mail was received via Mail-SeCure System. ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user This mail was received via Mail-SeCure System. -- Micha Silver Arava Development Co. +972-52-3665918 http://www.surfaces.co.il ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] DAtum Warning while using r.in.gdal
On Tue, 1 Jun 2010, Kim Besson wrote: Thanks to Paul and Micha for the help. About this: I defined my location using this image but instead of being reprojected with PROJ4 extension I used EPSG:3763 and then r.in.gdal. Then, using the same original image (in UTM) I reprojected to this CRS but using PROj4 extension (showed in my original message). What is the correct one? the bellow expression or the EPSG:3763 in order to reproject an image? It depends on what the original co-ordinate system of the image was. If it was in a different datum from ETRS89 or a different ellipsoid from GRS80/WGS84 (which is the datum/ellipsoid of your GRASS location), then there will be small errors in the reprojection because you didn't specify a datum for the target co-ordinate system. You can check the co-ordinate system of the original image by running: g.proj -p georef=L71203033_03320001023_B10.TIF If the two datums are the same (for our purposes it is reasonable to say this if the two ellipsoids are the same, or the difference is very small (e.g. GRS80 and WGS84)) then there is no problem at all. But in general you should specify the datum when doing a reprojection or warping as it can be important. It was only a warning. It imported the image nevertheless, without using -o option. And when I run r.in.gdal I get this warning: Datum unknown not recognised by GRASS and no parameters found Projection of input dataset and current location appear to match Yes the first line is a warning coming from the GRASS gproj library as it is converting the co-ordinate system; the second is simply an informational message from r.in.gdal - nothing to worry about there. Paul ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] DAtum Warning while using r.in.gdal
On Tue, 1 Jun 2010, Kim Besson wrote: [...] Coordinate System is: PROJCS[WGS 84 / UTM zone 29N, GEOGCS[WGS 84, DATUM[WGS_1984, Hi Kim, The datum of the original datum is WGS84, which is almost the same as GRS80, so your data will be fine. So there's nothing to worry about in this case, but read on for a more detailed explanation... [...] I just need to have this data in EPSG:3763 system so I thought that I would just need to define EPSG:3763 without anything else. Original is in WGS84 and this one is GRS80. As I said it is fine in this case because WGS84 and GRS80 are almost the same. But in general you always need to specify the datum you are reprojecting to. Your PROJ.4 string included +ellps=GRS80 to specify the ellipsoid, but that is *not* enough information to do a datum transformation; you also need to specify the datum transformation to WGS84. For GRS80 you can do this by adding +towgs84=0,0,0 to the PROJ.4 string (as well as +ellps=GRS80). Specifying EPSG:3763 to gdalwarp instead should also have exactly the same effect, although personally I prefer the PROJ.4 strings as you can see all the parameters and see exactly what is going on. What should I do? use in gdalwarp EPSG:3763 or the PROJ4 extension? It's up to you - there are several different ways of achieving the same thing! Paul ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] DAtum Warning while using r.in.gdal
On 05/31/2010 07:25 PM, Kim Besson wrote: Greetings Following a few suggestions made at this list I'm using gdalwarp to project a few landsat images and only then yusing r.in.gdal. I'm using this expression to reproject image: gdalwarp -t_srs +proj=tmerc +lat_0=39.668258 +lon_0=-8.1331084 +k=1 +x_0=0 +y_0=0 +ellps=GRS80 +units=m +no_defs L71203033_03320001023_B10.TIF landsat_out.tif And when I run r.in.gdal I get this warning: Datum unknown not recognised by GRASS and no parameters found Projection of input dataset and current location appear to match What does this means? There's no +datum= parameter in the CRS definition, so the new, projected tif has no datum information. But, if you're sure the above parameters are correct, you can ignore the warning and tell GRASS to ignore the warning with the -o option to r.in.gdal. BTW, how did you define the GRASS Location? with the EPSG:3763 or the above definition? If so, then you surely should have no problem importing with the -o (over-ride projection check) option. Thanks kim This mail was received via Mail-SeCure System. ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user This mail was received via Mail-SeCure System. -- Micha Silver Arava Development Co. +972-52-3665918 http://www.surfaces.co.il ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] DAtum Warning while using r.in.gdal
On Mon, 31 May 2010, Kim Besson wrote: Greetings Following a few suggestions made at this list I'm using gdalwarp to project a few landsat images and only then yusing r.in.gdal. I'm using this expression to reproject image: gdalwarp -t_srs +proj=tmerc +lat_0=39.668258 +lon_0=-8.1331084 +k=1 +x_0=0 +y_0=0 +ellps=GRS80 +units=m +no_defs L71203033_03320001023_B10.TIF landsat_out.tif And when I run r.in.gdal I get this warning: Datum unknown not recognised by GRASS and no parameters found Projection of input dataset and current location appear to match What does this means? It is a warning that there is no datum information in the reprojected file. It may not be a problem, unless if the original image (before you reprojected it) was in a different datum there could be small errors in it. Since the ellipsoid is GRS80, you can add the correct datum information by adding +towgs84=0,0,0 to the projection parameters. If you import that image with r.in.gdal then there should be no warning. Paul ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
