Frank and Scott, For Google Earth output (rather than Google Maps which would be in "google mercator") the output projection should be EPSG:4326, or WGS1984 Latitude Longitude.
Mike -- Michael Smith RSGIS Center US Army Corps of Engineers On 3/2/10 12:52 AM, "Frank Warmerdam" <warmer...@pobox.com> wrote: > scottd777 wrote: >> Hi, and thank heaven for GDAL! >> >> I was so happy to find this tool, but I am having some trouble figuring out >> the exact command I need for an image warping application. If there is >> someone who doesn't mind a newbie type question, I could really use the >> help! >> >> Essentially, I have imagery which is referenced with British National Grid. >> I am tyring to convert / warp this so that it can be used within Google >> Earth. I have reference points for the upper left and lower right of the >> image in Easting and Northing, and transformed those so that I got lat / >> long coordinates which line up very well within Google Earth, however it >> appears that the projection is off. >> >> I am hoping to use gdalwarp to convert the TIF file (referenced as >> mentioned), but I had some questions: >> - For the world file that I create for gdalwarp, should I include the >> Easting / Northing, or does this need to be lat / long? > > Scott, > > If the file is in the british national grid then the origin and pixel > size should be in british national grid meters. > >> - Can I just go straight to gdalwarp, or do I need to do some other >> translation first? > > If you have a TIFF with a world file you should be able to just proceed > directly with the warp. > >> - The command I am trying to use looks like this: >> gdalwarp -s_srs "proj=utm +zone=33v +datum=OSGB36" -t_srs "proj=latlong >> +datum=WGS84" filein.tif out.tif >> >> Is this the correct command to get from a BNG source ortho image to what >> would overlay correctly in something like Google Earth? > > I'm not google earth guru, but I had assumed that it expected imagery in > the "google mercator" projection, not in geographic lat/long as you have > targetted. I would instead use a command like: > > gdalwarp filein.tif out.tif -s_srs EPSG:27700 \ > -t_srs "+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 +nadgri...@null +wktext +no_defs" > > I don't believe british national grid is the same as UTM 33, and I don't > believe that a "v" in the zone indicator will mean anything to PROJ.4. > EPSG:27700 is the british national grid. > > I have provided the full definition of the google mercator projection > though shorter forms like EPSG:900913 or EPSG:3857 might work depending > on the version of GDAL and supporting files you have. > > scottd777 wrote: >> Please? Anyone? I'm sure the response will be really quick... > > Not such an easy answer, and I'm not sure it will be everything you > need. The problem with the popularity of Google Earth is that it > has introduced a flood of new people with little GIS background all > asking the same questions. > > Best regards, _______________________________________________ gdal-dev mailing list gdal-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/gdal-dev