[MapProxy] Rounding error in clipped WMS requests Was: (no subject)

Oliver Tonnhofer olt at omniscale.de
Sun Dec 16 23:35:17 PST 2012


see https://github.com/mapproxy/mapproxy/issues/48

My comment from the ticket:

It is a rounding error indeed. You are requesting a tile that is not completely within the boundaries of the grid (362800 vs. 350000) and MapProxy clips the source to that boundary in the WMS service. That clipping used floats for calculation that were converted to integers later (for PILs Image.paste), but the size calculation still used the floats and that resulted in one missing pixel line (int this case).

It is now fixed in b9deb20.

But I guess that you don't want to have this clipping at all if you are requesting tiles, since it will open, modify and save the tile for each request (at least for the first tile row in the north). So you should force MapProxy to use WMS-C with thetiled=True option. This will make sure that MapProxy won't modify any tiles (seehttp://mapproxy.org/docs/nightly/services.html#wms-c)

On 17.12.2012, at 03:36, Carpenter, Tim wrote:

> Hi,
> I am investigating a problem where MapProxy serves WMS images with transparent lines on their edges. I’ve found that this is easily repeatable with the example demo service on a clean install of MapProxy.
> If you install the latest version of MapProxy and fire up the demo service but change the wms_demo.html file to remove the singleTile option on the OpenLayers layer you get transparent lines between some of the map images. See WMSTileEdge.png. The attached file WMSTile.png has a 1px transparent line along the bottom edge where there should be data.
> Why is this? And is there a way to prevent it?
> I’ve tried changing many of the settings in the yaml config files (anything possibly related to transparency) to no great success. I can stop them happening but the effect is that the content outside of the boundary of the WMS becomes opaque which looks bad as well.
> Thanks,
> Tim
> <WMSTile.png><WMSTileEdge.png>_______________________________________________
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Oliver Tonnhofer    | Omniscale GmbH & Co KG    | http://omniscale.de
http://mapproxy.org | https://github.com/olt    | @oltonn

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