[GIS] Creating buffer in QGIS without including surface of original polygon

bufferpolygonqgis

I have to have a layer (shapefile) with a polygon that has a 100-m buffer zone around each polygon of my original file. With the QGIS Buffer (fixed distance) tool, I get polygons that include the original polygon. But I only want the outside for each polygon.
If the buffer for polygon A intersects the buffer for polygon B, I don't want to lose that part of the "outside" buffer (so I can't use the différenciation symétrique tool (sorry, I'm on a French version of software and I don't know it's equivalent in English). Alternative would be a smart intersection that is polygon-to-polygon based on an ID to get rid of the inner part.

My original datafile is the green and the buffers are underneath in blue.

Just the buffer layer that I tried in blue.

Best Answer

Let me suggest an approach by a Virtual Layer.

SELECT st_difference(st_buffer(Your_layer.geometry, 100), Your_layer.geometry)
FROM Your_layer

Please save this Virtual Layer as another vector file, such as ESRI Shapefile, before you proceed to next steps.

Related Solutions

R – Creating OUTSIDE_ONLY Buffer Around Polygon

There is no way to define "outside only" in gBuffer. You have to go through the additional step of turning the inner polygon to null, and for a good reason. You can use the raster::erase function to remove the internal polygon. If you really want this as part of the gBuffer function why not just write your own modification of gBuffer that adds an "outside only" argument?

Add required libraries and example data. I subset the first polygon and then use spTransfrom to account for gBuffer not accepting unprojected data.

library(raster)
library(rgeos)
library(rgdal)

p <- shapefile(system.file("external/lux.shp", package="raster"))
  p <- p[1,]
  p <- spTransform(p, CRS=CRS("+proj=merc +ellps=GRS80"))

Here we buffer the polygon and then use erase to turn the internal (original) polygon to null.

b <- gBuffer(p, width=1000, quadsegs=100)
plot(p)
  plot(b,add=TRUE)  

e <- erase(b, p)                             # using raster:erase
e <- rgeos::gDifference(b, p, byid=TRUE)     # using rgeos:gDifference
  plot(e, col="red")

Best Answer

Related Solutions

R – Creating OUTSIDE_ONLY Buffer Around Polygon

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