ftools "intersect" geoprocessing tool fails to gather all shapes

[jlortscher]

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 following:

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 features").

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 places/cities.

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.

[strk]

Doesn't ftools have its own bug tracker or mailing list ? Show one pair of geometries against which GEOSIntersect call fail for a valid ticket.