[MapProxy] scale difference wms-direct vs. mapproxy request

[Oliver Tonnhofer]

Hi Lars,

On 28.11.2010, at 18:37, Lars Lingner wrote:
> When I'm doing a direct request to the WMS (UMN MapServer) like this:
> 
> /cgi-bin/wms_servicep&EXCEPTIONS=XML&FORMAT=image/png&TRANSPARENT=false&VERSION=1.1.1&STYLES&request=GetMap&LAYERS=all&BBOX=4.21875,50.792047064406844,4.2626953125,50.81981826215653&width=256&height=256&SRS=EPSG:4326
> 
> ...I'm getting a tile back like [1]
> 
> The request to MapProxy looks like this:
> 
> /proxy_service?EXCEPTIONS=XML&FORMAT=image/png&TRANSPARENT=false&VERSION=1.1.1&STYLES&request=GetMap&LAYERS=all&BBOX=4.21875,50.792047064406844,4.2626953125,50.81981826215653&width=256&height=256&SRS=EPSG:4326
> 
> ...but results in an different styled tile [2]
> 
> The extent is the same, but the streets are styled slightly different
> and also the labels doesn't look the same.


You are requesting a different resolution than you are caching. MapProxy will respond to any WMS request, even if you are requesting "tiles" that do not exists. MapProxy scales the image if the resolution does not match or if the BBOX differ since it is a full WMS server (unlike Tilecache or Geowebcache). You can force WMS-C with tiled=true, then you should get errors that the BBOX of your tile request is invalid.

You have two options: You can either configure MapProxy to cache the resolutions you are requesting. You need to create a custom grid configuration. http://mapproxy.org/docs/latest/sources.html#debug might help to find the resolutions.

Or, you can change your client (OpenLayers?) to only request the resolutions you are caching. Look at the resolutions in the demo service: http://mapproxy.org/docs/latest/services.html#mapproxy-demo-service

Regards,
Oliver

-- 
Oliver Tonnhofer <olt at omniscale.de>
Omniscale - Dominik Helle, Oliver Tonnhofer GbR
Nadorster Str. 60, 26123 Oldenburg
Tel: +49(0)441/9392774-2 (Fax: 9)