Hi Frank,
Thank you very much. I have been ripping my hair out over that one.
Cheers,
Simon
Frank Warmerdam wrote:
Simon Haddon wrote:
Hi,
I wasn't quiet sure what subject heading to give this problem. I
hope it
is ok.
I have a map file which creates maps in decimal degrees. The data is a
mix raster and vector. It is the raster data which I am having trouble
with.
If I have any raster data with a large grid cell size (ie: 25 km) the
generated map always has complete pixels (cells) created. There are
never
any truncated pixels. As a result pixels don't even maintain their
correct relative position and can be seen differently, compared to the
overlayed point and polygon data, depending on how fair you move or
resize
the map.
If I move the map a whole pixel cell size the pixels redraw in their
correct position. If a move the map 1/2 a pixel cell size then the
pixels
move to fit the image. This can also extend to stretching the pixel
cells
to always ensure that a complete set of cells are displayed on the map
Has anyone had any experience with this problem and does anyone have any
suggestions about how to fix it.
Simon,
This is due to an optimization in MapServer to use the GDAL RasterIO()
call
for up/down sampling. The net result is that requests are always made
on "pixel boundaries" and you get the result you see. If you add the
line:
PROCESSING "RESAMPLE=NEAREST"
then MapServer will use a more general resampling code chunk which
will give
better results, but at some performance cost.
Best regards,
