Pixel Shift

[Steve Lime]

There's another bug floating out there (1957) that may be related as Frank noted. It was discovered using Open Layers with WMS tiles. Not sure if the problem is MapServer, GD or a combination of both. I suspected it may be a clipping problem but looking at your output I'm not so sure. Could also be a rounding error? (I'm beginning to hate tiling)

If you can upload your testcase to ftp.dnr.state.mn.us (put in pub/incoming someplace) I'll take a look...

Steve

>>> Jukka Sirviö <Jukka.Sirvio at ARBONAUT.COM> 11/03/06 1:16 AM >>>

There was no answers on mapserver users -list for this issue. Is this a
'known-problem'? We are able to reproduce with 4.8 and 4.10. Bugzilla
number 1956.

Jukka

----- Forwarded by Jukka Sirviö/arbonaut/fi on 03.11.2006 09:01 -----
                                                                           
             Teemu                                                         
             Mäkelä/arbonaut/f                                             
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                                       Jukka Sirviö/arbonaut/fi at mail       
             03.11.2006 08:29                                           cc 
                                                                           
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We are generating tiles for a uDig -based mapping application using
MapServer's WMS connection. We simply give the extents of each image
requested - extents are calculated so that we always gain images on size
1024 x 1024 pixels. Extend coordinates in WMS query should be ok.

The issue is that lines are uncontinuos on the border of the tiles. If line
crosses the tile border on the angle 45 - 90 degrees no problems appear.
However, if the angle is between 0 - 45 degrees the line is broken. See
attached image. On the image the yellow line respresents tile border and
the red line represents trail. White pixels are the MapServer's raster
intepretation of the red line. The problem is that the "trail" line is
broken (uncontinuous) on the border of tile.

(See attached file: broken_border.jpg)