Segment-Segment Intersection

Calculates intersection type and location for two line segments.

Installation

defp deps do
  [{:seg_seg, "~> 1.0"}]
end

Usage

Full Documentation

The SegSeg module provides a function intersection that calculates the intersection between two line segments and returns a tuple with three elements:

Boolean true if the two segments intersect at all, false if they are disjoint
An atom representing the classification of the intersection:

:interior - the segments intersect at a point that is interior to both
:vertex - the segments intersect at an endpoint of one or both segments
:edge - the segments are parallel, collinear, and overlap for some non-zero length
:disjoint - no intersection exists between the two segments

A tuple {x, y} representing the point of intersection if the intersection is classified as :interior or :vertex, otherwise nil.

Examples

SegSeg.intersection({2, -3}, {4, -1}, {2, -1}, {4, -3}) #=> {true, :interior, {3.0, -2.0}}
SegSeg.intersection({-1, 3}, {2, 4}, {-1, 4}, {-1, 5}) #=> {false, :disjoint, nil}
SegSeg.intersection({1, 2}, {3, 0}, {2, 1}, {4, 2}) #=> {true, :vertex, {2, 1}}
SegSeg.intersection({-1, 0}, {0, 2}, {1, 4}, {-1, 0}) #=> {true, :edge, nil}

Float Precision Issues

It is possible that floating point math imprecision can cause incorrect results for certain inputs. In situations where this may cause issues, an epsilon options is available. When set to true intersection comparisons are made with a very small epsilon based on the minimum of the lengths of the provided segment times a very small number (currently 0.0000000001). epsilon can also be set to a specific number that will be used as the epsilon value. This eliminates most rounding error, but of course could cause false results in certain situations. This currently only effects :vertex results but might be expanded to :edge in the future.

SegSeg.intersection({4, 3}, {4, 7}, {6.05, 9.05}, {3.95, 6.95}) #=> {true, :interior, {4.0, 6.999999999999998}}
SegSeg.intersection({4, 3}, {4, 7}, {6.05, 9.05}, {3.95, 6.95}, epsilon: true) #=> {true, :vertex, {4, 7}}

Tests