The ddrt from windfish-studio

Crash when inserting bounding box with triangular or zero area

I've been using this lib with great success but recently I've been hitting a bug with small bounding boxes crashing DDRT.

Isolating the issue from the stacktrace and getting to a minimal repro was pretty hard but after some debugging time I got there:

This is fine:

DynamicRtree.new(type: MerkleMap)
{:ok, t} = DynamicRtree.insert({0, [{9, 10}, {9, 10}]})
{:ok, t} = DynamicRtree.insert({1, [{9, 9}, {9, 9.1}]})

fine as well:

DynamicRtree.new(type: MerkleMap)
{:ok, t} = DynamicRtree.insert({0, [{9, 9.1}, {9, 9.1}]})

but this crashes (notice the bounding box is a really small triangle):

DynamicRtree.new(type: MerkleMap)
{:ok, t} = DynamicRtree.insert({1, [{9, 9}, {9, 9.1}]})

and this crashes as well (the bounding box has an area of 0):

DynamicRtree.new(type: MerkleMap)
{:ok, t} = DynamicRtree.insert({1, [{9, 9}, {9, 9}]})

The crash looks like this:

17:46:17.597 [error] GenServer DDRT terminating
** (ArgumentError) argument error
    :erlang.tl([])
    (ddrt 0.2.1) lib/ddrt/dynamic_rtree_impl/utils.ex:44: DDRT.DynamicRtreeImpl.Utils.combine_multiple/1
    (ddrt 0.2.1) lib/ddrt/dynamic_rtree_impl.ex:263: anonymous fn/3 in DDRT.DynamicRtreeImpl.add_entry/3
    (elixir 1.11.2) lib/map.ex:818: Map.update!/3
    (merkle_map 0.2.0) lib/merkle_map.ex:221: MerkleMap.update!/3
    (ddrt 0.2.1) lib/ddrt/dynamic_rtree_impl.ex:262: DDRT.DynamicRtreeImpl.add_entry/3
    (ddrt 0.2.1) lib/ddrt/dynamic_rtree_impl.ex:246: DDRT.DynamicRtreeImpl.insertion/3
    (ddrt 0.2.1) lib/ddrt/dynamic_rtree_impl.ex:79: DDRT.DynamicRtreeImpl.tree_insert/2
    (ddrt 0.2.1) lib/ddrt/dynamic_rtree.ex:506: DDRT.DynamicRtree.handle_call/3
    (stdlib 3.13.2) gen_server.erl:706: :gen_server.try_handle_call/4
    (stdlib 3.13.2) gen_server.erl:735: :gen_server.handle_msg/6
    (stdlib 3.13.2) proc_lib.erl:226: :proc_lib.init_p_do_apply/3

It only seems to appear when (1) the tree is empty, and (2) the bounding box is either a triangle or has a 0 area.

I gave solving this a few attempts but without success.

Here are two failing tests reproducing the issue:

    test "MerkleMap inserts a triangular bounding box without crash" do
      DynamicRtree.new(type: MerkleMap)

      {:ok, t} = DynamicRtree.insert({1, [{9, 9}, {9, 9.1}]})

      assert t == DynamicRtree.tree()

      root = t |> MerkleMap.get(:root)
      {ch, _root_ptr, root_box} = t |> MerkleMap.get(root)
      assert t |> Enum.to_list() |> length == t |> Enum.uniq() |> length
      assert length(ch) == 1
      assert root_box == [{9, 9}, {9, 9.1}]
    end

    test "MerkleMap inserts a zero area bounding box without crash" do
      DynamicRtree.new(type: MerkleMap)

      {:ok, t} = DynamicRtree.insert({1, [{9, 9}, {9, 9}]})

      assert t == DynamicRtree.tree()

      root = t |> MerkleMap.get(:root)
      {ch, _root_ptr, root_box} = t |> MerkleMap.get(root)
      assert t |> Enum.to_list() |> length == t |> Enum.uniq() |> length
      assert length(ch) == 1
      assert root_box == [{9, 9}, {9, 9}]
    end

Option to choose between Rtree or QuadTree as underlying data structure

We would really like to extend the library in such a way that the end-user can choose between an RTree or a QuadTree for the underlying data structure, while maintaining the distributed nature of the library.

It's not entirely clear when we'll have the time to make this change, but we would appreciate anybody willing to work with us to integrate this functionality into our library via a pull-request.

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Crash when inserting bounding box with triangular or zero area

Option to choose between Rtree or QuadTree as underlying data structure

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