Tile extent always a notch too big

Example of bad tiling

For the record, I'm not convinced this is a bug in the client. The tiles are placed such that their tiles line up -- right edge of the image is the right side of the right pixel, left side of the image is the left side of the left pixel.

I've never seen a case where the backend server has a problem like this, despite doing a lot of different setups.

I think that the server is to blame here.

See screenshot in attachement of the first post. The map is clearly having a problem. And if I request manually a tile around this zone, there is no problem. So my source data is good.

I did some experimenting with mapserver 5. You can find my stuff here:

http://www2.thus.ch/~patrick/tmp/

The sample.tif image is 22x22 pixels gdalinfo tells me that:

Driver: GTiff/GeoTIFF
Size is 22, 22
Coordinate System is `'
Metadata:
  TIFFTAG_DOCUMENTNAME=/home/pvalsecc/tmp/sample.tif
  TIFFTAG_IMAGEDESCRIPTION=Created with GIMP
  TIFFTAG_XRESOLUTION=72
  TIFFTAG_YRESOLUTION=72
  TIFFTAG_RESOLUTIONUNIT=2 (pixels/inch)
Corner Coordinates:
Upper Left  (    0.0,    0.0)
Lower Left  (    0.0,   22.0)
Upper Right (   22.0,    0.0)
Lower Right (   22.0,   22.0)
Center      (   11.0,   11.0)
Band 1 Block=22x22 Type=Byte, ColorInterp=Red
Band 2 Block=22x22 Type=Byte, ColorInterp=Green
Band 3 Block=22x22 Type=Byte, ColorInterp=Blue

Now, let say I want the image delimited by the blue lines (blue lines included). In mode=map, I need that:

http://www2.thus.ch/cgi-bin/mapserv?map=/home/patrick/public_html/tmp/test.map&mode=map&mapext=1.5+1.5+20.5+20.5&map_size=20+20

But, in mode=wms, here is the URL:

http://www2.thus.ch/cgi-bin/mapserv?map=/home/patrick/public_html/tmp/test.map&mode=wms&request=getMap&bbox=1,1,21,21&version=1.1&layers=test&srs=epsg:4269&format=image/png&width=20&height=20&styles=

You can try to alter both URL, you'll see...

So if you want to be correct, the tile extent you should use depends if you are in Layer.MapServer or in Layer.WMS:

• MapServer:

  var tileBounds =
      new OpenLayers.Bounds(tileoffsetlon + resolution/2.0,
                            tileoffsetlat + resolution/2.0,
                            tileoffsetlon + tilelon - resolution/2.0,
                            tileoffsetlat + tilelat - resolution/2.0);
  

• WMS:

  var tileBounds =
      new OpenLayers.Bounds(tileoffsetlon,
                            tileoffsetlat,
                            tileoffsetlon + tilelon,
                            tileoffsetlat + tilelat);
  

What do you think?

This makes more sense to me. Thanks for digging into it.

I'd like to confirm that this is expected behavior with the MapServer developers before we put this in -- it wouldn't be the first time we had broken MapServer -- but in general, I'm supportive of putting a change doing something like this in.

I have tested that with mapserver 4.10.3 and mapserver 5.0.0. They seem to have the same resolution/2.0 stuff, but 4.10.3 was having incoherent approximations between the two axis (x and y) in mode=map. Try my setup with this extent:

1+1+20+20

You'll see that a red line show up in only one direction.

My home server is in 5.0.0, so you'll have to check with your own install...

elem is taking this one

If anyone wants to actually confirm that this is the correct behavior, please put a patch in, and if it's done, we can put it into 2.6.