In Python, How to Encode and Decode Complex Data for a OWSLib WPS call to PyWPS-4?

Question

In Python, how can I encode "complex" (vector) data for a WPS call that just echoes back the data, and decodes the data from the result. I was planning on using OWSLib on the client side and PyWPS-4 on the server side.

This what I have so far for the server:

import flask
import pywps

class EchoVector(pywps.Process):
    def __init__(self):
        inputs = [pywps.ComplexInput('message',
                                     'Input message',
                                     supported_formats=[pywps.Format('application/gml+xml')],
                                     mode=pywps.validator.mode.MODE.STRICT)]

        outputs = [pywps.ComplexOutput('response',
                                       'Output response',
                                       supported_formats=[pywps.Format('application/gml+xml')])]

        super(EchoVector, self).__init__(
            self._handler,
            identifier='echo_vector',
            title='Echo Vector Test',
            abstract='Returns the given vector',
            version='1.0.0.0',
            inputs=inputs,
            outputs=outputs,
            store_supported=True,
            status_supported=True
        )

    def _handler(self, request, response):
        response.outputs['response'].data = request.inputs['message'][0].data

        return response

app = flask.Flask(__name__)

wps_processes = [EchoVector()]

service = pywps.Service(wps_processes)

@app.route('/wps', methods=['GET', 'POST'])
def wps():
    return service

bind_host='127.0.0.1'
app.run(threaded=True,host=bind_host)

This is what I have so far for the client:

import owslib.wps
import collections

url = "http://127.0.0.1:5000/wps"
wps = owslib.wps.WebProcessingService(url, verbose=False, skip_caps=True)
wps.getcapabilities()

process_name = "echo_vector"
inputs = [("message", owslib.wps.GMLMultiPolygonFeatureCollection([[(-102.8184, 39.5273),
                                                                    (-102.8184, 37.418),
                                                                    (-101.2363, 37.418),
                                                                    (-101.2363, 39.5273),
                                                                    (-102.8184, 39.5273)]]))]

execution = wps.execute(process_name, inputs)

for output in execution.processOutputs:
    owslib.wps.printInputOutput(output)

I get am getting an "Invalid mimeType value text/xml for input message" exception.

This code is also available in this GitHub repository

Answer 1

The problem here is that OGR’s ExportToGML doesn’t declare a namespace prefix / uri in the output, which would make the ExecuteResponse XML choke parsers. I've opened a GDAL ticket to address this.

In the meantime, as a workaround, you can adjust the output of ExportToGML as described here, i.e.:

def _setNamespace(xml, prefix, uri):
    return xml.replace('>', ' xmlns:%s="%s">' % (prefix, uri), 1)

better_gml = _setNamespace(geom.ExportToGML(), 'gml', 'http://www.opengis.net/gml')