[Gdal-dev] gdaladdo and MapServer's OFFSITE parameter

[Jeff McKenna]

I have a test case that produces odd results:

I have 2 geotiffs that have to reproject, add overviews, and tile. Here 
is what I found:

1. raw data tiled looks fine: 
http://www2.dmsolutions.ca/netbin/premiere/340401/original.gif

2. reprojected with gdalwarp, overviews with gdaladdo, and tiled, shows 
a sliver between the 2 images:

 > gdalwarp -s_srs EPSG:26916 -t_srs EPSG:102736 -of GTiff file1.tif 
./new/file1.tif

http://www2.dmsolutions.ca/netbin/premiere/340401/warped-with-overviews-no-offsite-sliver.gif 
http://www2.dmsolutions.ca/netbin/premiere/340401/warped-with-overviews-no-offsite-zoomed-into-line.gif

3. reprojected with gdalwarp, overviews with gdaladdo, tiled, using 
OFFSITE in mapfile:

 > gdaladdo -r average ./new/file1.tif 2 4 8 16

thinner sliver still exists at full extents (and several zooms after 
this): 
http://www2.dmsolutions.ca/netbin/premiere/340401/warped-with-overviews-with-offsite-sliver.gif

sliver does not exist when zoomed far in: 
http://www2.dmsolutions.ca/netbin/premiere/340401/warped-with-overviews-with-offsite-zoomed-into-line.gif

4. reprojected with gdalwarp, without overviews, tiled, and using 
OFFSITE in mapfile looks perfect:

http://www2.dmsolutions.ca/netbin/premiere/340401/warped-no-overviews-with-offsite.gif
http://www2.dmsolutions.ca/netbin/premiere/340401/warped-no-overviews-with-offsite-zoomed-in.gif

****

So there seems to be a problem with using gdaladdo and MapServer's 
OFFSITE parameter.

Am I doing something wrong, or am I missing a commandline switch somewhere?

I have the 2 test images and test mapfile for whoever wants to try this 
as well (I just can't distribute the images over this list).

thanks.

jeff


-- 
Jeff McKenna
DM Solutions Group Inc.
http://www.dmsolutions.ca