Difference between revisions of "Geometry Functions"
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| + | [[Tools]] | ||
| + | [[File:GeometryFunctions.png]] | ||
| − | + | Geometry Functions is a very rich tool. How it works depends highly on the geometry function you choose : | |
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| + | * '''Geometry functions using a mask''' - A mask is a layer containing a single geometry. The following functions will compare each geometry of the source layer to the mask. Note that the single geometry contained in the mask may be a MultiGeometry but not a GeometryCollection. The result contains as many features as the source layer. | ||
| + | ** ''Intersections'' - Creates features which are the intersection of source feature geometries with the mask. | ||
| + | ** ''Union'' - Creates features which are the union of each single feature of source layer with the feature geometry of mask. | ||
| + | ** ''Difference (A-B)'' - Substract geometry of the mask to each feature of the source layer. You can for example clean a layer by removing parts of feature geometries overlapping the ocean surface.. | ||
| + | ** ''Difference (B-A)'' - You may want to do the opposite : remove feature geometries from ocean area. | ||
| + | ** ''Symmetric difference'' - Symmetric difference will keep the part of source geometries which does not intersect the mask with the part of the mask which does not intersects the source geometry. | ||
Revision as of 23:08, 8 July 2011
Geometry Functions is a very rich tool. How it works depends highly on the geometry function you choose :
- Geometry functions using a mask - A mask is a layer containing a single geometry. The following functions will compare each geometry of the source layer to the mask. Note that the single geometry contained in the mask may be a MultiGeometry but not a GeometryCollection. The result contains as many features as the source layer.
- Intersections - Creates features which are the intersection of source feature geometries with the mask.
- Union - Creates features which are the union of each single feature of source layer with the feature geometry of mask.
- Difference (A-B) - Substract geometry of the mask to each feature of the source layer. You can for example clean a layer by removing parts of feature geometries overlapping the ocean surface..
- Difference (B-A) - You may want to do the opposite : remove feature geometries from ocean area.
- Symmetric difference - Symmetric difference will keep the part of source geometries which does not intersect the mask with the part of the mask which does not intersects the source geometry.