bufferextractoverlapping-featurespointr
In R, I have a raster stack with 6 variables. I would like to extract the mean and maximum value of each variable at 300 coordinates within a 500m buffer radius and a 1km buffer radius.
In ArcGIS 10.2 there are problems extracting variables from buffers if there is any overlap. Is this a problem in R?
If not, how do you make buffers around a point in R?
And how would I extract the mean and maximum value at the two scales surrounding each point?
Try a three step approach:
The image to the left shows the original buffers. The image to the right show the intersected buffers in red and the selected original buffers in turquoise.
I was able to achieve this in QGIS 3.2 using the following work flow. There's a few steps involved and several processing algorithms all from the processing toolbox. For the layers produced in the intermediate steps below, I would recommend keeping them as temporary layers rather saving to file.
Start with your layer of overlapping buffers.
On this layer, run the Union algorithm from the processing toolbox. This will produce an output layer which contains multiple duplicate features.
On this layer, run "Delete duplicate geometries". Now you should have a polygon layer with one feature for each of the overlapping sections of the original buffer layer. For some reason I ended up with invalid geometries at this point and had to run GRASS v.clean, so it may be advisable to do this also as an additional step.
Create centroids from your cleaned union layer.
Now run the algorithm "Join attributes by location (summary)". Use the centroids as the input layer and your original overlapping buffer layer as the join layer. Use "intersects" as the geometric predicate and for summaries to calculate select "count". This should produce a new point layer called "join layer" with a new field "value_count" which contains the number of overlapping segments from your buffer layer.
We now need to join that attribute back to the union layer. For this just use the algorithm "Join attributes by location". For the input layer, use your cleaned union layer and the newly created "joined layer" as the join layer. For fields to add select "value count" and for join type select: "take attributes of first located feature (one to one).
This should output a polygon layer also called "joined layer" which also has a field "value count" containing the number of overlapping buffer segments. I would recommend saving and renaming this layer. Here you can see this layer labelled and categorised with the "value count" field.
Best Answer
In your case, it is not necessary to create polygon buffers for your points. The raster::extract function has a buffer argument that will do exactly what you are after.
For future reference the rgeos::gBuffer function will allow you to create buffers, and if the by.id=TRUE argument is used the buffers will not be dissolved into a single feature class. These buffers can be passed to extract withour issues of overlapping polygons.