Thank you for your response Even. Unfortunately when I split the chart down the 180 degree longitude line, GDALSuggestedWarpOutput() still produces smaller chart dimensions than the dimensions of the inputs. I think this would rule out any wrapping problem because the split pieces exhibited the same behavior despite never crossing the dateline.
I am going to try and step through the GDALSuggestedWarpOutput() function and examine it's logic more closely. -- Joe On Wed, Dec 10, 2014 at 5:01 AM, Even Rouault <[email protected]> wrote: > "joem", > > It seems that your input dataset is very close to the dateline, and very > likely crossing it. I'm not that surprised that GDALSuggestedWarpOutput() > has > issues at that discontinuity. But I think it might have indeed operated > correctly. If the extent of the dataset crosses the dateline the resulting > eastings in Web Mercator coordinates will go from about -20 million to > about > 20 million. A huge width. GDALSuggestedWarpOutput() tries to scale the > computed dimensions so that the result has roughly the same number of > pixels > as the input. So the huge width becomes a reasonable width, and the > reasonable > height becomes a small height. > In that situation, you could try using modified input and output proj.4 > strings > by adding +over to the normal proj.4 definition. See > https://trac.osgeo.org/proj/wiki/GenParms > This should produce an output datasets with eastings that go beyond the 20 > million limit. You might want to cut it into 2 parts afterwards. > > Best regards, > > Even > > > > > > > I am working on a tool to project FAA charts from Lambert Conformal Conic > > to Web Mercator (EPSG 900913). It seems to be producing correct output > > except for a FAA chart of the East Aleutian Islands. When I traced the > > problem in my code, it appears that GDALSuggestedWarpOutput() is giving > me > > a width and height far too small given the input tiff had larger > > dimensions. The source GeoTiff has dimensions of 15555x5786 but > > GDALSuggestedWarpOutput() gives a suggested width of 17050 and a height > > of 178. A height of 178 pixels surely has to be wrong. I have added > > the well-known text and proj.4 output from gdalinfo.exe of the input > tiff > > below. Although I am not entirely sure if I should, I have been using > > the values supplied by GDALSuggestedWarpOutput() for creating my output > > Geotiff as if the output will always be valid. > > > > * Why is GDALSuggestedWarpOutput() giving bad values for the width and > > height of the output tiff? > > * Is this incorrect usage of GDALSuggestedWarpOutput() or is it a bug? > > > > > > PROJ.4 : '+proj=lcc +lat_1=54.66666666666666 +lat_2=49.33333333333334 > > +lat_0=52.16666666666666 +lon_0=-177.5 +x_0=0 +y_0=0 +datum=NAD83 > +units=m > > +no_defs ' > > > > OGC WKT : > > PROJCS["unnamed", > > GEOGCS["NAD83", > > DATUM["North_American_Datum_1983", > > SPHEROID["GRS 1980",6378137,298.2572221010002, > > AUTHORITY["EPSG","7019"]], > > AUTHORITY["EPSG","6269"]], > > PRIMEM["Greenwich",0], > > UNIT["degree",0.0174532925199433], > > AUTHORITY["EPSG","4269"]], > > PROJECTION["Lambert_Conformal_Conic_2SP"], > > PARAMETER["standard_parallel_1",54.66666666666666], > > PARAMETER["standard_parallel_2",49.33333333333334], > > PARAMETER["latitude_of_origin",52.16666666666666], > > PARAMETER["central_meridian",-177.5], > > PARAMETER["false_easting",0], > > PARAMETER["false_northing",0], > > UNIT["metre",1, > > AUTHORITY["EPSG","9001"]]] > > > > > > > > _______________________________________________ > > gdal-dev mailing list > > [email protected] > > http://lists.osgeo.org/mailman/listinfo/gdal-dev >
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