WMS tiles compressed vertically

[jreiser@…]

Tiles requested from an ESRI ArcGIS Server WMS service appear vertically compressed when added to JOSM via wmsplugin.

Two example WMS query strings:

NAIP PA East
​http://maps.pasda.psu.edu/wmsconnector/com.esri.wms.Esrimap?Servicename=NAIP&SERVICE=WMS&REQUEST=GetMap&VERSION=1.1.1&LAYERS=15599&STYLES=&FORMAT=image/jpeg&SRS=EPSG:4326&

State of Delaware
​http://datamil.delaware.gov/wmsconnector/com.esri.wms.Esrimap/DE_aerial07?SERVICE=WMS&REQUEST=GetMap&VERSION=1.1.1&LAYERS=1&STYLES=&FORMAT=image/jpeg&SRS=EPSG:4326&

[Cobra]

This also happens with other wms and with the newest version of josm (1951) and wmsplugin (16872).

[stoecker]

Still there? Provide examples/screenshots.

This sounds like wrong projection is used.

[John Reiser <jreiser@…>]

Screenshot of the bug occuring using the DE WMS.

[John Reiser <jreiser@…>]

Please see the attached screenshot. It seems the ESRI-generated WMS services have some issue with aspect. Loading a WMS layer from another service (ie USGS Topomaps) aligns correctly with the OSM data.

[stoecker]

Some questions:

• What projection settings do you have in josm
• What projection is used in the URL for ESRI request (srs= parameter)
• What projection does the ESRI server support (find out using GetCapabilities).

[John Reiser <jreiser@…>]

Switching to WGS84 Geographic does allow you to use the PA and DE WMSs in JOSM. Both of the URLs above use EPSG:4326. However, the NJ WMS works without issue in Mercator projection. The URL for the NJ WMS is: ​http://njwebmap.state.nj.us/njorthos?REQUEST=GetMap&SERVICE=WMS&layers=Natural2007&styles=&format=image/jpeg&srs=EPSG:4326&
It too uses EPSG:4326.

The NJ server returns the following available SRSs:
EPSG:3424 (NJ), EPSG:2959 (UTM 18N), EPSG:4269 (NAD 83), EPSG:4326 (WGS 84), EPSG:102711 (NJ)
While the DE server returns the following:
EPSG:102257, ESRI:102257, EPSG:2776, EPSG:4326, EPSG:4269, EPSG:4152, EPSG:26957

I guess my question is now, why does the NJ one work without a hitch and the others require switching the projection? What exactly is the Mercator projection JOSM uses? "Web Mercator"?

[stoecker]

Yes, JOSM uses Web Mercator. For cases of easy of use WMS plugin silently converts Web Mercator to EPSG:4326, which does introduce a slight error, but this should not be really relevant due to small tile sizes requested. The picture you get indicates some other calculation error somewhere (the error I mentioned above would be inside one tile and not at tile borders).