Handle non-900913 External WMS Servers Better

[sbenthall]

http://webmap.em.gov.bc.ca/liteview6.5/servlet/MapGuideLiteView

http://openmaps.gov.bc.ca/mapserver/admin-boundaries

[sbenthall]

To clarify, do you mean that these are WMS servers that won't load in the Map Composer?

[ingenieroariel]

Based on IRC discussion from the day this issue was reported, yes, these are layers that don't work in the Map Composer.

[ahocevar]

These layers don't work because they are not provided in EPSG:900913. This issue is related to #850, but the rabbit hole goes deeper. For http://openmaps.gov.bc.ca/mapserver/admin-boundaries, it would be enough to switch from 900913 to 3785, which is the same projection. But http://webmap.em.gov.bc.ca/liteview6.5/servlet/MapGuideLiteView only provides EPSG:4326, which is a different projection.

I currently see several ways for GeoNode to support layers in projections that are different from the base layer's:

1. Only list layers in the "Add Layers" dialog that support the map projection.
2. Use the GeoNode WMS as cascading WMS to reproject layers to the map projection.

The above options could be enhanced by making the map projection configurable. Once it is, a third option would be possible:

1. Do some kind of SRS negotiation on the client. This would work for all layer types that provide some kind of capabilities doc that advertises projections.

The next step to proceed with this ticket would be a decision on which of these options we want to persue. The list of options above is ordered by complexity of a client-side implementation.

[ingenieroariel]

http://ideg.xunta.es/wms/request.aspx is another service that doesn't show any layers in the composer.

[ingenieroariel]

Replying to [ticket:851 pramsey]:

http://webmap.em.gov.bc.ca/liteview6.5/servlet/MapGuideLiteView

http://openmaps.gov.bc.ca/mapserver/admin-boundaries

http://iws.erdas.com/imageX/ecw_wms.dll

http://apollo.erdas.com/erdas-apollo/map/CherokeeContext2006

[ingenieroariel]

The above service's doesn't work properly because they are in a different projection then the mapservice itself.

Openlayers can reproject webservices. Is this not a option to first check whether the mapservice is in the supported SRS, if not reproject the service layers into the supported SRS?

[ahocevar]

Replying to [comment:9 scrifec]:

Openlayers can reproject webservices. Is this not a option to first check whether the mapservice is in the supported SRS, if not reproject the service layers into the supported SRS?

OpenLayers can only reproject vector data, not map tiles. With GeoServer >= 2.1 (included in the GeoNode synth branch), you can add such services as cascading WMS. We're currently investigating a way to have GeoServer reproject WMS layers even if it is not configured to use them as cascading WMS source.

[ingenieroariel]

This is a valid issue.

I prefer option 2:

1. Use the GeoNode WMS as cascading WMS to reproject layers to the map projection.

[jj0hns0n]

Lets punt on this to 2.1

[ingenieroariel]

This is fixed in the remote services branch. At least a useable workaround where you add that remote server as a new service and use it instead of going directly through the composer.