{"id":497,"date":"2010-06-25T14:14:23","date_gmt":"2010-06-25T18:14:23","guid":{"rendered":"http:\/\/www.kralidis.ca\/blog\/?p=497"},"modified":"2015-11-11T08:53:43","modified_gmt":"2015-11-11T13:53:43","slug":"geoprocessing-with-ogr-and-pywps","status":"publish","type":"post","link":"https:\/\/www.kralidis.ca\/blog\/2010\/06\/25\/geoprocessing-with-ogr-and-pywps\/","title":{"rendered":"Geoprocessing with OGR and PyWPS"},"content":{"rendered":"

PyWPS <\/a>is a neat Python package supporting the OGC Web Processing Service<\/a> standard.\u00a0 Basic setup and configuration can be found in the documentation, or Tim’s useful post<\/a>.<\/p>\n

I’ve been working on a demo to expose the OGR Python bindings for geoprocessing (buffer, centroid, etc.).<\/p>\n

Here’s an example process to buffer a geometry (input as WKT), and output either GML, JSON, or WKT:<\/p>\n

from pywps.Process import WPSProcess\r\nimport osgeo.ogr as ogr\r\n\r\nclass Buffer(WPSProcess):\r\n def __init__(self):\r\n  WPSProcess.__init__(self,\r\n  identifier='buffer',\r\n  title='Buffer generator',\r\n  metadata=['http:\/\/www.kralidis.ca\/'],\r\n  profile='OGR \/ GEOS geoprocessing',\r\n  abstract='Buffer generator',\r\n  version='0.0.1',\r\n  storeSupported='true',\r\n  statusSupported='true')\r\n\r\n  self.wkt = self.addLiteralInput(identifier='wkt', \\\r\n   title='Well Known Text', type=type('string'))\r\n  self.format = self.addLiteralInput(identifier='format', \\\r\n   title='Output format', type=type('string'))\r\n  self.buffer = self.addLiteralInput(identifier='buffer', \\\r\n   title='Buffer Value', type=type(1))\r\n  self.out = self.addLiteralOutput(identifier='output', \\\r\n   title='Buffered Feature', type=type('string'))\r\n\r\n def execute(self):\r\n  buffer = ogr.CreateGeometryFromWkt( \\\r\n   self.wkt.getValue()).Buffer(self.buffer.getValue())\r\n  self.out.setValue(_genOutputFormat(buffer, self.format.getValue()))\r\n  buffer.Destroy()<\/pre>\n
 def _setNamespace(xml, prefix, uri):<\/pre>\n
  return xml.replace('>', ' xmlns:%s=\"%s\">' % (prefix, uri), 1)<\/pre>\n
 def _genOutputFormat(geom, format):<\/pre>\n
 if format == 'gml':<\/pre>\n
  return _setNamespace(geom.ExportToGML(), 'gml', \\\r\n     'http:\/\/www.opengis.net\/gml')<\/pre>\n
 if format == 'json':<\/pre>\n
  return geom.ExportToJson()<\/pre>\n
 if format == 'wkt':<\/pre>\n
  return geom.ExportToWkt()<\/pre>\n
Notes:<\/p>\n
    \n
  • _setNamespace is a workaround, as OGR’s ExportToGML doesn’t declare a namespace prefix \/ uri in the output, which would make the ExecuteResponse XML choke parsers<\/li>\n
  • _genOutputFormat is a utility method, which can be applied to any OGR geometry object<\/li>\n<\/ul>\n
    As you can see, very easy to pull off, integrates and extends easy.\u00a0 Kudos to the OGR and PyWPS teams!<\/p>\n\n\n