Removing elongated, "thin" parts of shapes using R

Question

I have a dataset with a lot of polygons, of which some are long and thin in shape (see image). I'd like to remove their "extremities".

Is there a tool/method to remove thin parts of a polygon in R?*

In the example, the elongated shapes vary in shape and thickness

• I thought about using a shape-ratio (e.g. perimeter/area, as described here), but that only allows me to remove complete polygons, whereas in some cases I'd like to preserve the "roundish" part of a polygon.
• I'd like to be able to experiment with thresholds to find a suitable setting for the "roundness".
• Removing thin rectangles from a shapely polygon seems like a similar problem, but I'd rather not use shapely

Answer 1

Try using buffer

1. Buffer with a negative distance, for example -50
2. Buffer with +60
3. Clip the buffers with your original polygons

Answer 2

Buffering with negative distance and then the positive distance (plus some extra to account for loss of detail) as suggested in this answer can be realized with this code (in R):

BUFFER_WIDTH = 10
    
# negative buffer removes parts of the polygons
poly = raster::buffer(poly, width= - BUFFER_WIDTH )
    
# positive buffer recreates shape from the remainders
poly = raster::buffer(poly, width=   BUFFER_WIDTH + (BUFFER_WIDTH * 0.1))

Comments:

• this will also work like a smoothing operation
• intersecting the buffers with your original polygons is only needed if you want the original (more detailed) outline
• you may want to filter small areas (red), that might be created by artifact leftovers after negative buffering. In R: poly_new <- drop_crumbs(poly, threshold = AREA_THRESH)

Result: Blue original polygon, green/red resulting polygon.