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Why should calculate convex hull and reverse i, j in rasterization? #4

@HyperMn

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@HyperMn

Hi @fazanham , recently I work on extracting ground from some city scene ply. And your code help me a lot, that's a wonderful work! But I have two questions that puzzle me for some time.

  1. in TerrainFilter.cpp line 57 and line 92, I want to know why does the code calculate the convex hull before rasterization, and then determine whether each point is in the convex hull. I think convex hull is calculating by these points, so every point should in the convex hull?
  2. Still in TerrainFilter.cpp line176, in double loop(i, j), rasterize is stored by that j is the row index, i is the column index, while other 2d arrays is stored by reversal ways. I wonder if some knowledge is behind the storing way?

Hope to get your reply soon:)

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