<br><div class="gmail_quote">Hi, <br><br>I am trying to convert a GIF image into a georeference tiff image. Since I don't know the exact projection used to create the original image I downloaded from a website, I am trying to use various projections in an attempt to get the right one. On an ealier post it was suggested to use cs2cs command to convert the lat/lon corner points to projected coordinates I could assign to -a_ullr when creating the tiff.<br>
<br>I am running cs2cs and gdal_translate included in FWTools-2.0.6 in a RedHat Linux host.<br><br>These are the 2 commands I run to create the gtiff assuming the projection is Polar Stereographic with central meridian=-98.19:<br>
1) <b>cs2cs +proj=latlon +to +proj=stere +lat_0=90 +lat_ts=70 +lon_0=-98.19 -r<<EOF >stere98pts.dat<br>+44.0 135.0W <br>+20.0 74.0W<br>EOF</b><br><br>where Upper Left map corner: 44N 135W<br> Lower Right map corner: 20N 74W<br>
<br>2) using the points created by command 1) and assigning them to ulx, uly, lrx, and lry respectively I run:<br><br><b>ulx=-3150617.86<br>uly=-4209985.73<br>lrx=3545943.53<br>lry=-7893766.64<br>gdal_translate -of GTiff -co PROFILE=GEOTIFF -co INTERLEAVE=PIXEL -a_srs '+proj=stere +lat_0=90 +lat_ts=70 +lon_0=-98.19' -a_ullr $ulx $uly $lrx $lry my_image.gif my_image_stere98.tif</b><br>
<br>The info for the tiff image looks like:<br><i>Driver: GTiff/GeoTIFF<br>Files: my_image_stere98.tif<br>Size is 864, 526<br>Coordinate System is:<br>PROJCS["unnamed",<br> GEOGCS["WGS 84",<br> DATUM["unknown",<br>
SPHEROID["unnamed",6378137,298.2572235629972]],<br> PRIMEM["Greenwich",0],<br> UNIT["degree",0.0174532925199433]],<br> PROJECTION["Polar_Stereographic"],<br>
PARAMETER["latitude_of_origin",70],<br> PARAMETER["central_meridian",-98.19],<br> PARAMETER["scale_factor",1],<br> PARAMETER["false_easting",0],<br> PARAMETER["false_northing",0],<br>
UNIT["metre",1,<br> AUTHORITY["EPSG","9001"]]]<br>Origin = (-3150617.859999999869615,-4209985.730000000447035)<br>Pixel Size = (7750.649756944443652,-7003.385760456272692)<br>Metadata:<br>
AREA_OR_POINT=Area<br>Image Structure Metadata:<br> INTERLEAVE=BAND<br>Corner Coordinates:<br>Upper Left (-3150617.860,-4209985.730) (135d 0'0.00"W, 44d 0'0.00"N)<br>Lower Left (-3150617.860,-7893766.640) (119d56'53.85"W, 20d58'17.68"N)<br>
Upper Right ( 3545943.530,-4209985.730) ( 58d 5'0.89"W, 42d 4'44.10"N)<br>Lower Right ( 3545943.530,-7893766.640) ( 74d 0'0.00"W, 20d 0'0.00"N)<br>Center ( 197662.835,-6051876.185) ( 96d19'9.49"W, 37d52'39.33"N)<br>
Band 1 Block=864x9 Type=Byte, ColorInterp=Palette<br> Color Table (RGB with 256 entries)<br> 0: 0,0,0,255<br> 1: 0,255,255,255<br> 2: 153,153,102,255<br> 3: 204,204,204,255<br> 4: 255,0,0,255<br> 5: 51,153,204,255</i><br>
........ color table follow here .......<br><br><br>Unfortunately, I cannot see this image using a third party software that allows me to see other conversions of this same GIF using lcc and lcc2 conversions.<br><br><b>Q1: Am I converting lat/lon points correctly?<br>
<br>Q2: Am I using gdal_translate correctly?<br></b><br><br>I'd appreciate it any help to determine what I am doing wrong with this stereographic conversion.<br><br>
Thanks<br><br><br><br>
</div><br>