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handle cases where multiple endpoints are colinear as non-intersecting for line segments (because otherwise it cannot be used to check if intersection() has undefined behaviour, as there will be an infinite number of intersections)

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This commit is contained in:
Patrick Brosi 2018-08-17 15:07:20 +02:00
parent 95ce5ba03d
commit 69a360c48f
2 changed files with 10 additions and 4 deletions
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8
src/util/geo/Geo.h
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@ -398,9 +398,13 @@ inline bool contains(const std::vector<GeometryA<T>>& multigeo,
// _____________________________________________________________________________
template <typename T>
inline bool intersects(const LineSegment<T>& ls1, const LineSegment<T>& ls2) {
// two line segments intersect of there is a single, well-defined intersection
// point between them. If more than 1 endpoint is colinear with any line,
// the segments have infinite intersections. We handle this case as non-
// intersecting
return intersects(getBoundingBox(ls1), getBoundingBox(ls2)) &&
(contains(ls1.first, ls2) || contains(ls1.second, ls2) ||
contains(ls2.first, ls1) || contains(ls2.second, ls1) ||
(((contains(ls1.first, ls2) ^ contains(ls1.second, ls2)) ^
(contains(ls2.first, ls1) ^ contains(ls2.second, ls1))) ||
(((crossProd(ls1.first, ls2) < 0) ^
(crossProd(ls1.second, ls2) < 0)) &&
((crossProd(ls2.first, ls1) < 0) ^

6
src/util/tests/TestMain.cpp
View file

@ -972,12 +972,14 @@ CASE("geometry") {
EXPECT(geo::intersects(lsa, lsb));
EXPECT(geo::intersects(lsa, lsa));
EXPECT(geo::intersects(lsb, lsb));
EXPECT(!geo::intersects(lsa, lsa));
EXPECT(!geo::intersects(lsb, lsb));
EXPECT(!geo::intersects(lsa, lsc));
EXPECT(!geo::intersects(geo::Point<double>(871569.2, 6104550.4), geo::Point<double>(871581.2, 6104536), geo::Point<double>(871580.3, 6104541.3), geo::Point<double>(871625.7, 6104510.1)));
EXPECT(!geo::intersects(geo::Point<double>(0, 0), geo::Point<double>(1, 1), geo::Point<double>(0.5, 0.5), geo::Point<double>(1.5, 1.5)));
geo::Line<double> l{geo::Point<double>(1, 1), geo::Point<double>(2, 2), geo::Point<double>(2, 4)};
EXPECT(!geo::contains(geo::Point<double>(1, 2), l));
EXPECT(geo::contains(geo::Point<double>(2, 2), l));