[WFS/WCS] Add support POST requests

[salvafern]

Hello there! 👋

An issue I have faced using ows4R is that CQL/OGC (or viewParams via vendor params) filters fail if you try to perform a spatial query with a very detailed feature. See https://github.com/lifewatch/eurobis/issues/16

This is because URLs have a limit in the number of characters they can have in GET requests. Hence a possible solution is to allow POST and pass polygons there.

Example with curl:

Get all features that intersect with a certain polygon. I will use the EEZ layer of MarineRegions.

Create a post request as XML and name as xmlquery.xml. Contains the name of the layer (MarineRegions:eez), the name of the geometry column (the_geom), the instructions to intersect and the polygon to intersect with as gml

<wfs:GetFeature xmlns:wfs='http://www.opengis.net/wfs' xmlns:ogc='http://www.opengis.net/ogc' xmlns:gml='http://www.opengis.net/gml' service='WFS' version='1.0.0'>
  <Query typeName='MarineRegions:eez'>
	<ogc:Filter xmlns:gml="http://www.opengis.net/gml">
		<Overlaps>
		  <PropertyName>the_geom</PropertyName>
		  <gml:Polygon srsName="http://www.opengis.net/gml/srs/epsg.xml#63266405">
			<gml:outerBoundaryIs>
			  <gml:LinearRing>
				 <gml:coordinates>-0.258498799963897,58.4594990974729 2.76925390761733,58.4594990974729 2.76925390761733,53.7259702166065 -0.258498799963897,58.4594990974729</gml:coordinates>
			  </gml:LinearRing>
			</gml:outerBoundaryIs>
		  </gml:Polygon>
		 </Overlaps>
	</ogc:Filter>
  </Query>
</wfs:GetFeature>

Perform POST request with curl:

curl -XPOST -d @wfsquery.xml -H "Content-type: application/xml" "http://geo.vliz.be/geoserver/MarineRegions/ows?" --output test.geojson

From https://github.com/EMODnet/EMODnetWFS/issues/115#issuecomment-1384197510

Is this something feasible? Is there another approach we are overlooking?

Thanks!

[eblondel]

@salvafern yes POST would be the right approach but POST is not supported yet for WxS in ows4R. It is for CSW.

[salvafern]

I understand this is not trivial and would require some work. For now I just wanted to raise the issue to document. Thanks @eblondel !

[eblondel]

yes indeed it requires some work. ows4R POST request encoding is done generically. There is need to test / apply this other services than CSW. If I find some time, I'll give it a try for some basic WFS requests.