[Mapserver-users] gdaladdo

[Vincent Schut]

On Wednesday 05 March 2003 11:34, Manuel Marichal Pérez wrote:
> Hi all.
>
> I've got an application which deal with large TIFF's raster images. I
> considered to use GDAL to improve the
> performance (gdaladdo & gdaltndex). I succesfully compiled GDAL in my
> machine. Also I recompiled
> mapserver with "--without-tiff" and "--with-gdal" options.
>
> Then I used gdaladdo with one of my tiff images in order to make a TIFF
> image with many levels. Right.
>
> Now, what must I do with my "map" file to get the correct image be
> displayed as the user changes the scale?.

There is some explanation in on the mapserver website. You need to combine the 
minscale/maxscale items in the layer objects of your mapfile (see 
http://mapserver.gis.umn.edu/doc36/mapfile-reference.html#layer ) and the 
tile feature ( see http://mapserver.gis.umn.edu/doc36/raster-howto.html ).

However, it sounds like you might not be interested in tiling your dataset, 
but just using scaled down versions when viewing at larger scales. I think 
you'd better use gdal_translate then, as you need to create a separate file 
for each scaled down layer, instead of a built-in overview. Afaik, the 
mapfile does not support using one of many overviews of a tiff file as a 
datasource. I think. If I'm wrong, please somebody correct me.
So the correct procedure would be: create several scaled down versions of your 
dataset, at the scales that you want, and define a layer object for each of 
these, with minscale and maxscale items defined so that always just one will 
be drawn.

If you really want a performance gain, I think you should consider image 
tiling next to using different scale levels. See the explanation in the 
raster howto and search the mailing list archives for more info on the best 
way to do this. There have been some posts about it, if I remember well.

Regards,
Vincent Schut.
>
> Thanks in advance.

-- 
______________________________________
Vincent Schut (schut at sarvision.com)
Sarvision B.V.
Wageningen, The Netherlands
www.sarvision.com