How to provide a WFS in multiple projections

Question

I would like to set-up an editable web feature service (WFS-T) for serving my geospatial data. The data tables are in a PostGIS database on the same server. For security reasons my server admin doesn't allow remote connections to the Postgresql database. So I'm looking at using the WFS service. Clients will view and edit the data in QGIS or using a OpenLayers javascript client.

I succeeded in installing the TinyOWS software and setting up the transactional WFS.

However, I have an extra requirement: All data layers must be available in 3 projections: EPSG:3857, EPSG:3067, EPSG:4326.

Right now each table has a column the_geom with coordinates in the Finnish projection EPSG:3067.

What would you recommend to add the support for the other projections? Does the server like TinyOWS do "on the fly" re-projection on each request, or do I need to add extra geometry columns with coordinates in the other projections to each of my tables?

Answer 1

I found the answer to my question, so I'm posting it here in case somebody has a similar problem:

First, it's a bad idea to have multiple geometry columns in the same PostGIS table. One geometry column in the same projection as the original data is enough. Mapserver itself takes care of the on-the-fly reprojection. The on-the-fly reprojection by Mapserver is fast and performance can be further increased by caching.

In order to inform the client which projections my WFS layer supports, the following setting must be set in my .map file:

WEB
IMAGEPATH "/ms4w/tmp/ms_tmp/"
IMAGEURL "/ms_tmp/"
METADATA
  "wfs_title"          "WFS Demo Server for MapServer" ## REQUIRED
  "wfs_onlineresource" "http://mapserver.example.com/cgi-bin/wfs?" ## Recommended
  "wfs_srs"            "EPSG:4326 EPSG:3857 EPSG:3067" ## Recommended
  "wfs_abstract"       "This text describes my WFS service." ## Recommended
  "wfs_enable_request" "*"  # necessary
END
END

The following document clarified the issue for me: http://mapserver.org/ogc/wfs_server.html