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

Carpenter, Tim t.carpenter at fugroworld.com
Mon Dec 17 00:00:51 PST 2012

Thanks, Oliver.

I just applied your patch to my environment and that has cleared up the

Yes, you're certainly right that WMS-C would make more sense.


-----Original Message-----
From: Oliver Tonnhofer [mailto:olt at omniscale.de] 
Sent: Monday, 17 December 2012 3:35 PM
To: Carpenter, Tim
Cc: mapproxy at lists.osgeo.org
Subject: Rounding error in clipped WMS requests Was: [MapProxy] (no


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

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
> MapProxy mailing list
> MapProxy at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/mapproxy


Oliver Tonnhofer    | Omniscale GmbH & Co KG    | http://omniscale.de
http://mapproxy.org | https://github.com/olt    | @oltonn

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