gmap bathymetry layer returned improperly pixelated with a broad request.

[warmerdam]

The following reasonable look WMS request:

http://www2.dmsolutions.ca/cgi-bin/mswms_gmap?LAYERS=bathymetry&REQUEST=GetMap&SERVICE=WMS&FORMAT=image/jpeg&STYLES=&HEIGHT=625&VERSION=1.1.1&SRS=EPSG:4326&WIDTH=956&BBOX=-178.218524639424,-87.5565240606026,178.218524639424,87.5565240606026&TRANSPARENT=TRUE&EXCEPTIONS=application/vnd.ogc.se_inimage

returns an unreasonably pixellated response. That server is MS 5.2.1 but the same has been reported in trunk too. I believe it relates to reprojection from another projection for that layer, but I'm not sure. The setup is the standard gmap demo data.

danmo also mentions:

I found that if you change the ymin in the bbox to 0 instead of -87, the pixel size is fine. so it may be a problem with the way the warping algorithm picks its pixel size

[dmorissette]

To reproduce this locally, download the gmap demo from ​http://dl.maptools.org/dl/gmap-ms46.tar.gz and change the URL above to:

http://127.0.0.1/cgi-bin/mapserv?map=/path/to/gmap/htdocs/gmap75_wms.map&LAYERS=bathymetry&...

[warmerdam]

Digging deeper today...

[warmerdam]

The problem here is that the corner -178,-87 transforms to projected coordinate -345361185, -88127889 which is geometrically meaningless and due to the projection not being valid in this area.

Unfortunately we have no machinery to recognise that we are well beyond the sensible bounds of the projected coordinate system and PROJ.4 is returning values - just not sensible values.

I'm not sure what to do about this.

Putting off for the time being.