[gdal-dev] GDALSuggestedWarpOutput() problem

[Even Rouault]

"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"]]]
> 
> 
> 
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