[Mapserver-users] strange results when displaying grid

[Frank Warmerdam]

Ted Quinby wrote:
> I have an Arc/Info Binary Grid I'm trying to display in Mapserver.  When 
> displayed in ArcView or ArcMap, the grid is fine -- pixel values ranging 
> from 1 to 8 and all in the right place.
> 
> However, when displaying this grid in Mapserver, a strange thing 
> happens.  A small 32 x 32 pixel square appears in the eastern portion of 
> the grid.  In further evaluating this 32 x 32 pixel square, pixels that 
> should have a value of 3 are being drawn as if the pixel value was 1 and 
> pixels that should have a value of 4 are being drawn as 0.  This only 
> occurs within this square -- all other pixel values are drawn correctly.
...
> Am I dealing with a corrupted grid somehow or is Mapserver 
> reading/displaying a valid grid incorrectly?
> 
> Anybody experience something similar or have any debugging thoughts?

Ted,

It is likely you have a slightly old version of GDAL with bugs in the
AIG driver.  There were recent fixes made to it to fix one block type
where offsets were not properly applied, and another block type that
wasn't supported at all.  I suspect you are running into one of those
bugs.  I would encourage you to upgrade to the GDAL 1.2.1 release and see
if the problem goes away.

Best regards,

-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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and watch the world go round - Rush    | Geospatial Programmer for Rent