Polygon union and area

I have a set of simple polygons that are randomly distributed over a given region. Basically what I want to do is to find the total area covered by a subset of them. Currently, I am using a combination of 'polybool' and 'polyarea' to accomplish this.

The problem is that I have to do this a number of times with different subsets of the polygons. Are there any other functions or tricks I could use to improve the runtime?

For the most part I am just adding a polygon to an existing set. I store the union of the polygons between iterations so I do not need to calculate the entire union every time. However, I also have to perform "subtract" operations. If I was to just remove polygon A from union(A,B,C) then that would not be correct since there might be regions of A that B and C cover. So I am forced to recalculate the entire union again. Would there be a more efficient way to do this?

Thank you.

Answer 1

[Walter Roberson]

Divide the area into sections, and for each section store the list of polygons that are partly or fully inside the section. When a particular polygon is removed, you only need to recalculate the union for the sections that the removed polygon touched.