[geos-devel] [GEOS] #521: ftools "intersect" geoprocessing tool fails to gather all shapes

GEOS geos-trac at osgeo.org
Tue Mar 27 18:46:25 EDT 2012

#521: ftools "intersect" geoprocessing tool fails to gather all shapes
 Reporter:  jlortscher  |       Owner:  geos-devel@…              
     Type:  defect      |      Status:  new                       
 Priority:  major       |   Milestone:  3.3.3                     
Component:  Default     |     Version:  3.3.2                     
 Severity:  Unassigned  |    Keywords:  intersect ftools          
 In QGIS, I used the ftools "intersect" geoprocessing tool and got
 unexpected results. It collected only those shapes that are entirely
 within the intersecting shape but missed shapes that are partially inside
 and partially outside of the intersecting shape.

 Below is an example using QGIS 1.7.4:

 Example: Using TIGER line shapefiles (downloaded from
 http://www.census.gov/geo/www/tiger/tgrshp2011/tgrshp2011.html), I do the

 1. Create a new QGIS project, and add shapefiles for Illinois "Places"
 (i.e. cities) and for Illinois "Counties".
 2. Select Cook County in the Counties shapefile.
 3. Open the window for vector:geoprocessing tools:intersect
 4. Specify Places as the Input vector layer (do not mark "use only
 selected features")
 5. Specify Counties as the Intersect layer (mark "use only selected

 My expectation is that the result set will contain all of the places
 (cities) that are partially or entirely within Cook County, IL. However,
 the result set contains only those places (cities) that are entirely
 within Cook County. Those places that are only partially inside of Cook
 County are missing. For example, the City of Chicago, of which 99% is in
 Cook County is missing from the result set as are a number of other

 The version of ftools is 0.6.1 (appears to be the most recent). I do not
 know what version of GEOS is being used.

Ticket URL: <http://trac.osgeo.org/geos/ticket/521>
GEOS <http://geos.refractions.net/>
GEOS (Geometry Engine - Open Source) is a C++ port of the Java Topology Suite (JTS).

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