Feature request #6445
Better documentation for the Intersect and Clip tools
|Category:||Documentation and Help|
|Pull Request or Patch supplied:||No||Resolution:|
From the documentation (I've inserted the (a) and (b):
(a) Intersect: Overlay layers such that output contains areas where both layers intersect.
(b) Clip: Overlay layers such that output contains areas that intersect the clip layer.
When I read these descriptions I think that (b) is saying the output layer will contain all the features from the input layer which intersect the clip layer, and (a) is saying the output layer will be trimmed by the intersect layer, i.e. it will contain all the same features as the output from (b), but they will be trimmed.
1. Isn't this the wrong way round? Shouldn't (a) be called "clip" (or "trim"), and (b) be called "intersect"?
2. Why do I get the same results (trimmed) using both tools? (testing on Windows with both polyline and polygon input layers)
Or do I misunderstand something?
#1 Updated by Alister Hood about 5 years ago
(c) Difference: Overlay layers such that output contains areas not intersecting the clip layer.
The output of this is the opposite of the output of (a) and (b).
When I read the description I think it is saying this is supposed to be the opposite of (a). If my argument (1) is correct it should be reworded to make it clear that this is the opposite of the "clip" tool, not the opposite of the "intersect" tool.
#2 Updated by Giovanni Manghi about 5 years ago
- Priority changed from Normal to Low
- Status changed from Open to Feedback
I would suggest to place this questions in the users or developers mailing list, rather than filing them as a ticket. Anyway I will have a look to your notes during the developer meeting, but right now I don't see anything particularly wrong about those operations. At least from the geometries point of view they should behave the same as in other gis packages.
#3 Updated by Alister Hood about 5 years ago
Giovanni Manghi wrote:
At least from the geometries point of view they should behave the same as in other gis packages.
But surely there shouldn't be two different tools that do exactly the same thing, should there? That's the main reason I filed it as a ticket.
#5 Updated by Alister Hood about 5 years ago
- Category changed from 44 to Documentation and Help
Intersect and Clip do do different things, but my data wasn't suitable to demonstrate the difference.
Clip trims each feature in the input layer so that only the area which overlaps with any feature in the clip layer is left.
When a feature in the input layer overlaps more than one feature in the intersect layer, Intersect also splits it into separate features. I'll try to come up with a better description of the Intersect tool for the documentation, but I need to sleep now :)
#6 Updated by Alister Hood about 5 years ago
When I read these descriptions I think that (b) is saying the output layer will contain all the features from the input layer which intersect the clip layer
Of course, to do this you would actually use "Vector>Research tools>Select by location" (and then save the selection as a new file if that's what you need).
And you can also do the opposite with the same tool, by first selecting all the features in the layer, and using the option to remove the matching features from the selection.