Latitude tile origin in WMS Layer moves randomly making it unusable for caching

[openlayers]

Our WMS server does tile caching and we noticed that, using openlayer, no request hit the cache but generate a lot of tiles in the cache.
Further investigation showed that the tiles have a different origin in the latitude (the longitude one is always correct) every time the user does the following:

1. change the zoom level
2. pan the map
3. return to the previous zoom level

See attached some example tiles from the same location at the same zoom level after doing the above.

Browser used: Firefox 3.0 / WinXP

[openlayers]

sample of cached tiles

[crschmidt]

John,

The configuration of your map will help more than the zipfile yu'e uploaded. Can you please create a minimal test case demonstrating the problem as an HTML file?

[crschmidt]

Oh, and I forgot to mention: I'd guess that your'e using Google Maps as a base layer, with or without 'reproject': true on, but *not* with sphericalMercator set to true. If this is the case, the problem is that you're not using spherical mercator: "Don't do that."

[openlayers]

 http://www.aeridigitals.com/tiletest.html[[BR]]

i have given the tiles a green border so the problem is easier to spot.

[crschmidt]

Well, what I get is IIS errors, but. :)

Yes, this is expected behavior. (A WONTFIX.) If you want to overlay tiles for caching on top of Google Maps, use SphericalMercator.

[openlayers]

Replying to crschmidt:

Oh, and I forgot to mention: I'd guess that your'e using Google Maps as a base layer, with or without 'reproject': true on, but *not* with sphericalMercator set to true. If this is the case, the problem is that you're not using spherical mercator: "Don't do that."

Yes that is true, but ...
Our WMS server does tiles for EPSG:4326 (similar to GoogleMaps). I've noticed that at low zoom levels our imagery moves further north. This is no problem for us.
The problem mentioned above does not relate to this though. The tiles at the same location and the _same_ zoom level move randomly in the latitude direction.
Hope that helps...

[openlayers]

Ups .. i guess the "br" should not be in that url :-).

[crschmidt]

This is demonstrating a known/expected behavior when laying over Google Maps in a mode other than SphericalMercator . The library does not promise a fixed grid in this situation (due to the non-static north-south resolution used by Google Maps when treated as degrees).

This is entirely tied to not using SphericalMercator, and will not be changed in the library.