[MS4W-Users] Strategies for dealing with large area Mr SID files
jmckenna at gatewaygeomatics.com
Mon Oct 4 16:20:28 EST 2010
On 10-10-04 5:16 PM, Bill Harbour wrote:
> I have eight Mr SID images that cover my County (1,500 square miles). I
> used gdaltindex to build a tile index of the Mr SID’s and created a
> layer for that tile index in the map file. t takes mapserver about 10 or
> more seconds to display the raster. Do any of you guys have
> suggestions-strategies for improving the display times of the images??
I agree that 10 or more seconds to display your images in a mapfile is
unacceptable. (by the way, for testing mapfile speeds I always
recommend using the shp2img utility, with the "-all_debug 5" switch, as
What I have done in the past, when using a large area of images, is to
use a generalized image of the area when zoomed out (in GeoTIFF format),
and then when users zoom in switch to the actual tileindexed MrSIDs. Is
that a possibility for you?
Also, do your MrSID files have overviews embedded in them? I believe
GDAL should be able to use these overviews for faster drawing.
Of course, for speed in MapServer, I must tell you that the optimal
configuration is to have all of your rasters in GeoTIFF format (possibly
converted with gdal_translate http://www.gdal.org/gdal_translate.html),
with overviews for each GeoTIFF generated by gdaladdo
(http://www.gdal.org/gdaladdo.html), and then indexed with the
gdaltindex utility. But I understand the GeoTIFFs might not be an
option for you.
Hopefully one of the points above is useful for your situation.
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