[mapserver-users] WFS GetFeature sometimes returns 'missing' even when there are matching features

[Gertjan van Oosten]

Hi,

A WFS GetFeature request like this one:

  <wfs:GetFeature xmlns:wfs="http://www.opengis.net/wfs" service="WFS" version="1.1.0" xsi:schemaLocation="http://www.opengis.net/wfs http://schemas.opengis.net/wfs/1.1.0/wfs.xsd" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
    <wfs:Query typeName="feature:Results_wfs">
      <wfs:PropertyName>FEATURE_ID</wfs:PropertyName>
    </wfs:Query>
  </wfs:GetFeature>

sometimes returns 'missing' like so:

  <?xml version='1.0' encoding="ISO-8859-1" ?>
  <wfs:FeatureCollection
     xmlns:ms="http://mapserver.gis.umn.edu/mapserver"
     xmlns:gml="http://www.opengis.net/gml"
     xmlns:wfs="http://www.opengis.net/wfs"
     xmlns:ogc="http://www.opengis.net/ogc"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="http://mapserver.gis.umn.edu/mapserver http://localhost/mapserv?SERVICE=WFS&VERSION=1.1.0&REQUEST=DescribeFeatureType&TYPENAME=feature:Results_wfs&OUTPUTFORMAT=text/xml;%20subtype=gml/3.1.1  http://www.opengis.net/wfs http://schemas.opengis.net/wfs/1.1.0/wfs.xsd">
     <gml:boundedBy>
	<gml:Null>missing</gml:Null>
     </gml:boundedBy>
  </wfs:FeatureCollection>

even when there is a matching feature. This happens with Mapserver 6.4.1
and Oracle 11.2. I've traced it down to the searchrect in msQueryByRect()
inside mapquery.c being "empty":

  {minx=-1, maxx=-1, miny=-1, maxy=-1}

This is caused by the way the extent is computed:

   msOracleSpatialLayerGetExtent. Using this Sql to retrieve the extent:
   SELECT SDO_GEOM.SDO_CONVEXHULL(link_geo, 0.001000) AS GEOM from (...)

The convex hull is NULL for some features. As the documentation says:

  http://docs.oracle.com/cd/E11882_01/appdev.112/e11830/sdo_objgeom.htm#SPATL1114
  "The function returns a null value if geom1 is of point type, has
  fewer than three points or vertices, or consists of multiple points
  all in a straight line."

I indeed have features like that, so in this case no features are
returned at all. That is obviously not right. If I add these three lines
it works correctly and my features are returned:


--- mapserver-6.4.1/mapquery.c.distrib	2014-01-02 13:41:49.000000000 +0100
+++ mapserver-6.4.1/mapquery.c	2014-07-17 13:58:36.000000000 +0200
@@ -1055,30 +1055,33 @@
 
     searchrect = map->query.rect;
     if(lp->tolerance > 0) {
       layer_tolerance = lp->tolerance;
 
       if(lp->toleranceunits == MS_PIXELS)
         tolerance = layer_tolerance * msAdjustExtent(&(map->extent), map->width, map->height);
       else
         tolerance = layer_tolerance * (msInchesPerUnit(lp->toleranceunits,0)/msInchesPerUnit(map->units,0));
 
       searchrect.minx -= tolerance;
       searchrect.maxx += tolerance;
       searchrect.miny -= tolerance;
       searchrect.maxy += tolerance;
     }
+    if (searchrect.minx == -1 && searchrect.maxx == -1 && searchrect.miny == -1 && searchrect.maxy == -1) {
+      searchrect = map->extent;
+    }
 
     msRectToPolygon(searchrect, &searchshape);
 
     /* Raster layers are handled specially. */
     if( lp->type == MS_LAYER_RASTER ) {
       if( msRasterQueryByRect( map, lp, searchrect ) == MS_FAILURE)
         return MS_FAILURE;
 
       continue;
     }
 
     /* Paging could have been disabled before */
     paging = msLayerGetPaging(lp);
     msLayerClose(lp); /* reset */
     status = msLayerOpen(lp);


I.e if the query rectangle can't be computed for some reason, fall back
to the map extent. I don't know if this is the best fix, but it is the
simplest that I could find. Is this the right way to do it?

Kind regards,
-- 
-- Gertjan van Oosten, Principal Consultant, West Consulting B.V.
-- gertjan at West.NL     +31 15 2191 600       www.west.nl