在网格上查找外边缘

Question

I am working with an algorithm that has a grid of constructed dots, each with an X and Y coordinate. The grid is split into several procedural areas. I am looking for a way to find the outer edges of each area (different areas are indicated by different colors) via the vertices present in these areas. I have a 2D array of all the vertices in the grid, as well as 2D arrays for each individual area, containing all of the vertices in that area.

I am now wondering how to create an algorithm that finds the outer edges of each area, while discounting the "inner" parts. I am currently using C# in Unity3d, but programming language isn't really important. I'm looking for a general algorithm of how this would hypothetically be done. I do not quite know where to start

Answer 1

You can identify an edge-dot like this:

It is a dot that (any of):

• has a neighbor that is of different color than itself
• it is on the edge of the grid.

Algorithm: Loop through all the dots and test each dots (up to) 4 neighbors to determine if either of the two above points applies.

Complexity: O(n) (in the number of dots)