[mapserver-users] Missing row of pixels in MapServer generated tiles

[Roger André]

This is probably more of a TileCache question, than a MapServer one, but I
figure one of you may have had the same issue in the past.  I'm using
MapServer to feed TileCache a fairly large GeoTiff with global extents,
which I'm then displaying in Google Maps as a tile layer.  This has worked
well in the past, but now I'm encountering a weird problem.  Some of my
tiles are being rendered by MapServer with a row of pixels missing on the
bottom of the image.  So for example, in Zoom Level 2, all of the 0.png
tiles will be 256 x 256 pixels, but row 256 will not contain data from my
global image, but instead will be set entirely to whatever background color
I have set in my Mapfile. The problem appears in multiple, but not all, Zoom
levels, and at different geographic locations, but always at the bottom row
of a tile.

The source image doesn't have the lines in then, so I have to believe that
the "dead" row is an artifact of the rendering process.  My seed image is in
lat/lon WGS84, and the tiles are being requested in EPSG:900913.  The
reprojection seems to be working correctly, insofar as image lineup with
Google Maps seems to indicate.  If I take the seed image and create a very
reduced resolution version of it, then run it through TileCache, I don't get
any lines.  So it seems like the lines *might* be a result of downsampling,
but since they're not present at the bottom of every image, I'm not
convinced that's the problem.

Oh, and I'm using the GD driver.

Any ideas?

Roger
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