Problem with reprojected images

[Dirk Jesko]

Ed,

I already thought of something like this already. However, this should 
not happen. If the images are seamless (our images are seamless and do 
not have any borders) in the original projection, they should also be 
seamless after a reprojection. Otherwise, I would call it a bug.

I just tested an older version of Mapserver (4.6.1). That one creates 
seamless results, even if the images are reprojected. Only newer 
versions (tested 4.8.1) produce non-seamless images. Can someone confirm 
this?


Regards,
Dirk



Ed McNierney wrote:

>Dirk -
>
>I assume your tiled source images do not overlap, and that the originals
>do not have white border strips around them.
>
>If that's the case, this may be an inevitable artifact of the
>reprojection.  Look at the situation along one north/south edge between
>two tiles.
>
>If you render the tiles in the source projection you'll get two adjacent
>vertical lines along the edges of each file, with no gap between them.
>
>If you reproject the tiles, then you will have two adjacent edges that
>are two diagonal lines.  The distance between the edges may not be 1,
>and may vary by a pixel along the course of those two diagonal lines.
>When that happens, the images will sometimes overlap by one pixel (you
>won't notice) and will sometimes leave a one-pixel gap (which is
>obvious).  The obvious gaps will repeat in a regular pattern since the
>phase difference between the two diagonal lines will be regular and
>repeating.
>
>	- Ed
>
>Ed McNierney
>President and Chief Mapmaker
>TopoZone.com / Maps a la carte, Inc.
>73 Princeton Street, Suite 305
>North Chelmsford, MA  01863
>ed at topozone.com
>(978) 251-4242 
>
>-----Original Message-----
>From: UMN MapServer Users List [mailto:MAPSERVER-USERS at LISTS.UMN.EDU] On
>Behalf Of Dirk Jesko
>Sent: Tuesday, March 14, 2006 3:04 AM
>To: MAPSERVER-USERS at LISTS.UMN.EDU
>Subject: [UMN_MAPSERVER-USERS] Problem with reprojected images
>
>Hi,
>
>I set up a WMS for aerial images. The images are projected in
>Gauss-Krueger 3 and have a size of one square kilometer. The WMS also
>provides other projections, e.g. Gauss-Krueger 2-5, UTM, etc. If I query
>the WMS with a projection other than the original one, I get little
>white lines along the edges of the tiles (see the attached image). The
>image format does not matter. How do I get rid of these? I can not find
>any option that might be related to this. By the way, this also happens
>if the data is accessed via mapscript or as normal cgi.
>
>Thanks for any help.
>
>Regards,
>Dirk
>
>  
>