[Mapserver-users] MapServer raster 'cracking' problem

[kenboss]

> From: Omry Yadan <omry at telmap.com>
> Subject: [Mapserver-users] MapServer raster 'cracking' problem
> Date: Wed, 5 Nov 2003 13:06:58 +0200
> 
> I have a problem with raster image generated by map server where the data
> source is tiled.
> The problem is that in some zoom levels (zoomed out), I get a white line
> between two tiles sometimes.
> I ran a test with two tiles only, and I could reproduce the problem.
> the tiles boundaries are exactly one next to the other - to strengthen the
> point :
> when I zoom into the merge line, I don't see a gap between the two tiles.
> Initially, my data was in ECW format - to rule out ECW related issue, I
> converted the data to GeoTiff, and I got the exact same problem (which
> appeared at the exact same requests.
> 
> Any help would be appreciated.
> 
> 	Omry.

Could it be that you've got some small sliver of "offsite" pixels at the edges 
of your tiles?  If so, you can address this problem through an OFFSITE parameter 
in your raster layer definition.  For example, if your offsite data value is 255 
(which would render as white), you might declare a layer like:

  LAYER
    NAME "imagery"
    STATUS default
    TILEINDEX "/path/to/tileindex/shapefile.shp"
    TILEITEM "LOCATION"
    TYPE raster
    OFFSITE 255 255 255
  END

This will cause mapserver to ignore any pixels with value 255 as it renders your 
output image.  Note that you need to declare OFFSITE as an RGB value regardless 
of whether your imagery is single- or multi-band.

HTH,

Ken Boss
MN DNR Forestry Resource Assessment