Consider using POST requests when passing large filters

[salvafern]

I have noticed when using ows4R that, when you pass a large filter (e.g. a complex WKT polygon), the request may fail because of the GET limitations. We could look into passing large filters via POST requests.

[maelle]

Interesting! So should we just switch to POST when passing any filter?

[salvafern]

Ideally yes! I have done this before via curl but haven't had the time to try in R

[maelle]

is this actually a ows4r feature request or do you have an example?

From what I see in https://github.com/eblondel/ows4R/blob/632928a100b69e1ca60f10975c38d3325016d97b/R/WFSGetFeature.R#L21, I'm not sure where one would pass "POST".

[maelle]

@salvafern friendly reminder about the question above :smile_cat:

[salvafern]

Yes sorry. Most likely it would be a new feature for ows4r, I don't see an option to do POST requests there. I include an example below:

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

But OGC filter are very verbose, not sure if this is something that will be solved quickly/easily.

Some resources:

• https://docs.geoserver.org/stable/en/user/services/wms/vendor.html#filter
• https://docs.geoserver.org/stable/en/user/filter/function_reference.html#geometric-functions
• https://docs.geoserver.geo-solutions.it/edu/en/vector_data/filter.html

[maelle]

@salvafern thank you! Would you mind opening a ows4r feature request then?

[salvafern]

@maelle Done! :)