I am trying to find points that fall within a polygon. Both layers are vector ESRI shapefiles. I used the fTools based intersect under Vector>GeoprocessingTools>Intersect. The output is an empty shapefile and I get the following warning:
Warnings: Feature geometry error: One or more output features ignored due to invalid geometry. Some output geometries may be missing or invalid.
I first tried this with layer of ~519 points and a complex polygon layer outline of the city limits of a city. I then made a new shapefile with just 6 points with some inside and some outside a polygon in a separate layer that I also drew. I got similar results. With this error:
Feature geometry error: One or more output features ignored due to invalid geometry. Some output geometries may be missing or invalid.
I used the geometry check tool to check both layers and got no errors.
If I use the same two simple layers and clip the point layer with the polygon layer I get what I want (i.e. all the points that fall within the polygon but not those outside the polygon). If I use the spatial query tool (Vector>SpatialQuery) I get the results I want as a selection.
In my original use and with the simple polygons, both shapefiles share the same CRS.
My question is, am I misunderstanding what the Geoprocessing tool Intercept does or am I missing some requirement of this tool or is it just working incorrectly?