[Gdal-dev] arcinfo grid gotcha

[Matt Wilkie]

Hi all,

Stumbled across a "gotcha" this afternoon when using the Windows gdal 
utilities v1.1.8 (from openev_fw distribution) and ArcInfo binary grids
(v1.1.9 info at end):

* If you type a trailing slash, the internal AIG grid driver is used.
* If you omit the slash, the external GIO driver is used.
* Because the two drivers have different abilities, the output may not 
be what you expect. In particular the number format (byte, int32, etc) 
and projections are different (or absent).
* It doesn't seem to matter which slash is used (\ or /).

 > gdal_translate arcinfo_grid/ aig.tif
 > gdalinfo aig.tif

Driver: GTiff/GeoTIFF
Size is 6927, 6799
Coordinate System is:
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["Albers_Conic_Equal_Area"],
     PARAMETER["standard_parallel_1",61.66666666666666],
     PARAMETER["standard_parallel_2",68],
     PARAMETER["latitude_of_center",59],
     PARAMETER["longitude_of_center",-132.5],
     PARAMETER["false_easting",500000],
     PARAMETER["false_northing",500000],
     UNIT["metre",1,
         AUTHORITY["EPSG","9001"]]]
Origin = (183318.249099,624474.799031)
Pixel Size = (17.490628,-17.490628)
Corner Coordinates:
Upper Left  (  183318.249,  624474.799) (138d10'18.18"W, 59d59'32.80"N)
Lower Left  (  183318.249,  505556.021) (137d59'16.23"W, 58d55'35.54"N)
Upper Right (  304475.828,  624474.799) (136d 0'27.34"W, 60d 4'16.47"N)
Lower Right (  304475.828,  505556.021) (135d53'36.67"W, 59d 0'10.44"N)
Center      (  243897.038,  565015.410) (137d 0'54.78"W, 59d30'11.08"N)
Band 1 Block=6927x1 Type=Byte, ColorInterp=Gray
   NoData Value=255


 > gdal_translate arcinfo_grid gio.tif
 > gdalinfo gio.tif

Driver: GTiff/GeoTIFF
Size is 6927, 6799
Coordinate System is `'
Origin = (183318.249099,624474.799031)
Pixel Size = (17.490628,-17.490628)
Corner Coordinates:
Upper Left  (  183318.249,  624474.799)
Lower Left  (  183318.249,  505556.021)
Upper Right (  304475.828,  624474.799)
Lower Right (  304475.828,  505556.021)
Center      (  243897.038,  565015.410)
Band 1 Block=6927x1 Type=Int32, ColorInterp=Gray
   NoData Value=-2.14748e+009


With gdal 1.1.9 compiled under cygwin only the GIO driver is used, with 
or without a trailing slash. This is undesirable because the AIG driver 
is superior, at least with the data we use. (Presumably one could 
compile v119 without GIO). Is there a mechanism to force which driver is 
used to read the source data set?


-- 
matt wilkie
--------------------------------------------
Geographic Information,
Information Management and Technology,
Yukon Department of Environment
10 Burns Road * Whitehorse, Yukon * Y1A 4Y9
867-667-8133 Tel * 867-393-7003 Fax
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