[Mapserver-users] Raster Projection

[Frank Warmerdam]

Hubert Fröhlich wrote:
> Frank,
> 
> what is (roughly) the difference between native TIFF/GeoTIFF support and 
> support by gdal? Seems that gdal is more capable? (you mentioned 
> reprojection)

Hubert,

The built-in TIFF support is simple and "light".  It supports 8bit
greyscale and 8bit paletted images (stripped, but not tiled).  It reads
geotiff origin and scale info, but no other geotiff formulations.  It
does not support 24bit input.

It is suitable to use when you want a lightweight mapserver without
any dependence on GDAL and the things it drags along.

The GDAL GeoTIFF support support virtual all geotiff forms, including
tiled, non-eight bit, fast loading from tiff overviews and support
for reading the geotiff projections using the PROJECTION "AUTO"
mechanism.  Also, the code that renders from GDAL supports various
extra features like projection "AUTO", reprojection, band selection,
24bit images, 24bit to 8bit via a color cube (with or without dithering.

GDAL, and the GDAL rendering code in MapServer should be considered
the "deluxe" raster support.  The builtin PNG, GIF, and TIFF drivers
should mainly be used when you want to avoid linking in GDAL.

> What happens if I compile with native tiff support AND gdal support? 
> Does this make sense? (Or should I REALLY compile only with 
> --without-tiff  ? )

In 3.5 the native TIFF driver would be used in preference to the GDAL
one, even in cases that it couldn't handle.  This was often bad.  In 3.7
the code tries to be smart and switch to using the GDAL code in various
cases the built-in driver can't handle, but it doesn't always pick properly.
I believe the 3.6.x code is similar to 3.5 in selectin built-in vs. GDAL.

If you have GDAL I would encourage you to build --without-tiff to avoid

Best regards,

-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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