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I try to clip shape "a" with shape "b". The result should be a polygon with the attributes and borders of "a" but cliped on the extent of "b". Basically a simple clip as we know it from ArcMap or QField. Now I want to use the sf package in R. But all the suggestions I find tell me to use````st_intersection```. But this is not actually a clip because it will result in a layer containing also the borders of "b".

a<-st_read("a.shp")
be<-st_read("b.shp"
Clip1<- st_intersection(a,b)

What I want

What I want

what st_intersection does

what st_intersect does

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  • What are the black dots in your diagram? Are the green, blue, and grey areas separate features? – Spacedman Oct 30 '20 at 17:42
  • There is no st_intersect function in sf. There's st_intersects, which tests for intersection, and there's st_intersection, which seems to do exactly what you want. – Spacedman Oct 30 '20 at 17:50
  • Yes they are separate features. My problem is, that a intersection preserves the feature boundaries of the intersect feature as you can see in the second image. I solved this problem now by using st_union on the intersect feature before the intersection. But it is odd that there is no command to do this directly. – sfetan Nov 3 '20 at 8:21
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This all works for me:

> library(sf)
> plot(input$geom, col=input$colour)
> plot(clip$geom, col=NA, border="red", add=TRUE)

enter image description here

> output = st_intersection(input, clip)
> plot(output$geom, col=output$colour)

enter image description here

The output object has the attributes from the underlying input object:

> output 
Simple feature collection with 3 features and 1 field
geometry type:  POLYGON
dimension:      XY
bbox:           xmin: 350715.5 ymin: 556199.3 xmax: 378850.3 ymax: 579962.8
CRS:            27700
  colour                       geometry
1  green POLYGON ((365346.3 579873.5...
2   grey POLYGON ((377844 569519.7, ...
3   blue POLYGON ((354933 574695.8, ...
>
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  • Yes for your case this works. But if your "clip" layer consists of multiple features overlaying the "input" layer, these feature are as well integrated into the "output" layer. I found a solution to use st_union for the "clip" layer before the intersection. – sfetan Nov 3 '20 at 8:17
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    This case is exactly the example of "what I want" from your question. You show the clip feature as a single feature. If you'd shown it as two semicircles then I'd have suggested unioning the clipping features. – Spacedman Nov 3 '20 at 11:03
  • 1
    You're right I replaced the images. – sfetan Nov 3 '20 at 14:42

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