Algorithms.Geometry.DelaunayTriangulation.DivideAndConquer

Divide & Conqueror Delaunay Triangulation

delaunayTriangulation :: (Ord r, Fractional r) => NonEmpty (Point 2 r :+ p) -> Triangulation p r

Computes the delaunay triangulation of a set of points.

Running time: \(O(n \log n)\) (note: We use an IntMap in the implementation. So maybe actually \(O(n \log^2 n)\))

pre: the input is a *SET*, i.e. contains no duplicate points. (If the input does contain duplicate points, the implementation throws them away)

delaunayTriangulation' :: (Ord r, Fractional r) => BinLeafTree Size (Point 2 r :+ p) -> Mapping p r -> (Adj, ConvexPolygon (p :+ VertexID) r)

Implementation

firsts :: ConvexPolygon (p :+ VertexID) r -> IntMap VertexID

Mapping that says for each vtx in the convex hull what the first entry in the adj. list should be. The input polygon is given in Clockwise order

fromHull :: Ord r => Mapping p r -> ConvexPolygon (p :+ q) r -> Adj

Given a polygon; construct the adjacency list representation pre: at least two elements

merge

Arguments

:: (Ord r, Fractional r)

=> Adj

-> Adj

-> LineSegment 2 (p :+ VertexID) r

lower tangent

-> LineSegment 2 (p :+ VertexID) r

upper tangent

-> Mapping p r

-> Firsts

-> Adj

Merge the two delaunay triangulations.

running time: \(O(n)\) (although we cheat a bit by using a IntMap)

type Merge p r = StateT Adj (Reader (Mapping p r, Firsts))

type Firsts = IntMap VertexID

moveUp :: (Ord r, Fractional r) => (VertexID, VertexID) -> VertexID -> VertexID -> Merge p r ()

Merges the two delaunay traingulations.

rotateR :: (Ord r, Fractional r) => VertexID -> VertexID -> Vertex -> Merge p r (Vertex, Bool)

'rotates' around r and removes all neighbours of r that violate the delaunay condition. Returns the first vertex (as a Neighbour of r) that should remain in the Delaunay Triangulation, as well as a boolean A that helps deciding if we merge up by rotating left or rotating right (See description in the paper for more info)

rotateR' :: (Ord r, Fractional r) => VertexID -> VertexID -> Vertex -> Vertex -> Merge p r Vertex

The code that does the actual rotating

rotateL :: (Ord r, Fractional r) => VertexID -> VertexID -> Vertex -> Merge p r (Vertex, Bool)

Symmetric to rotateR

rotateL' :: (Ord r, Fractional r) => VertexID -> VertexID -> Vertex -> Vertex -> Merge p r Vertex

The code that does the actual rotating. Symmetric to rotateR'

Primitives used by the Algorithm

qTest :: (Ord r, Fractional r) => VertexID -> VertexID -> Vertex -> Vertex -> Merge p r Bool

returns True if the forth point (vertex) does not lie in the disk defined by the first three points.

insert :: (Num r, Ord r) => VertexID -> VertexID -> Merge p r ()

Inserts an edge into the right position.

rotateToFirst :: VertexID -> Firsts -> Merge p r ()

make sure that the first vtx in the adj list of v is its predecessor on the CH

insert' :: (Num r, Ord r) => VertexID -> VertexID -> Mapping p r -> Adj -> Adj

Inserts an edge (and makes sure that the vertex is inserted in the correct. pos in the adjacency lists)

delete :: VertexID -> VertexID -> Adj -> Adj

Deletes an edge

isLeftOf :: (Ord r, Num r) => VertexID -> (VertexID, VertexID) -> Merge p r Bool

Lifted version of Convex.IsLeftOf

isRightOf :: (Ord r, Num r) => VertexID -> (VertexID, VertexID) -> Merge p r Bool

Lifted version of Convex.IsRightOf

Some Helper functions

lookup' :: Ord k => Map k a -> k -> a

size' :: BinLeafTree Size a -> Size

rotateTo :: Eq a => a -> CList a -> CList a

an unsafe version of rotateTo that assumes the element to rotate to occurs in the list.

pred' :: CList a -> CList a

Adjacency lists are stored in clockwise order, so pred means rotate right

succ' :: CList a -> CList a

Adjacency lists are stored in clockwise order, so pred and succ rotate left

focus' :: CList a -> a

nub' :: Eq a => NonEmpty (a :+ b) -> NonEmpty (a :+ b)

Removes duplicates from a sorted list

withID :: (c :+ e) -> e' -> c :+ (e :+ e')

lookup'' :: Int -> IntMap a -> a