[MapProxy] Distortion around antimeridian/date line with EPSG:3338

[Bruce Crevensten]

I'm trying to use MapProxy to present OpenStreetMap layers in a nonstandard
projection, EPSG:3338 (Alaska Albers).  The end goal is to use this as a
base layer in an app that adds other layers showing historical sea ice
extent around Alaska, which is why this (or a similar polar projection) is
needed.

Instead of a clean map, I'm seeing extreme distortion around the
antimeridian/date line.  Screenshot of distortion around antimeridian/date
line is here:

https://github.com/ua-snap/mp-config/blob/master/distortion-example.png

For this test case, I'm using a barely-modified version of the included
example configuration, only adding EPSG:3338 to the SRS that the WMS
supports.  My configuration that recreates the image above is here:

https://github.com/ua-snap/mp-config/blob/master/mapproxy.yaml

I've tried a few configuration variations within MapProxy and gotten the
same results.  In particular, I configured things according to the
directions here:

http://mapproxy.org/docs/1.6.0/configuration_examples.html#reprojecting-tiles

That approach also yielded distortion.

I found some online posts stating that adding proj4 +over parameter to the
epsg definitions could solve the issue, per this link:
http://lists.osgeo.org/pipermail/mapproxy/2010-December/000301.html

…but it didn't work.  To ensure that I was pointing at the correct proj4
definitions, I added the proj_data_dir parameter to MapProxy config and
verified it was using the same definitions I was modifying -- it was using
the correct file.

I was also careful to repeatedly clear out the cache during different
configuration attempts, to prevent a case where a valid configuration was
present but invalid cache data was being used.  No luck.

Software versions are:
MapProxy: 1.6.0
OS: CentOS 6.4 (Final)
Proj4: version 4.7.1

I'm using the serve-devel method for running MapProxy, with this command:
mapproxy-util serve-develop mapproxy.yaml

Am I seeing a rendering bug, or a misconfiguration issue within MapProxy?

Help greatly appreciated,
- Bruce

-- 
*Bruce Crevensten*
*
*
*Senior Software Engineer
*
(SNAP) Scenarios Network for Alaska & Arctic Planning
www.snap.uaf.edu

*Engineering Coordinator*
(ACUASI) Alaska Center for Unmanned Aerial Systems Integration
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