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Diffstat (limited to 'src/mbgl/util/geometry_util.cpp')
-rw-r--r-- | src/mbgl/util/geometry_util.cpp | 129 |
1 files changed, 129 insertions, 0 deletions
diff --git a/src/mbgl/util/geometry_util.cpp b/src/mbgl/util/geometry_util.cpp new file mode 100644 index 0000000000..df4119ce6a --- /dev/null +++ b/src/mbgl/util/geometry_util.cpp @@ -0,0 +1,129 @@ +#include <mbgl/util/geometry_util.hpp> + +#include <algorithm> + +namespace mbgl { + +template <typename T> +bool GeometryUtil<T>::rayIntersect(const Point<T>& p, const Point<T>& p1, const Point<T>& p2) { + return ((p1.y > p.y) != (p2.y > p.y)) && (p.x < (p2.x - p1.x) * (p.y - p1.y) / (p2.y - p1.y) + p1.x); +} + +// check if point p is on line segment with end points p1 and p2 +template <typename T> +bool GeometryUtil<T>::pointOnBoundary(const Point<T>& p, const Point<T>& p1, const Point<T>& p2) { + // requirements of point p on line segment: + // 1. colinear: cross product of vector p->p1(x1, y1) and vector p->p2(x2, y2) equals to 0 + // 2. p is between p1 and p2 + const auto x1 = p.x - p1.x; + const auto y1 = p.y - p1.y; + const auto x2 = p.x - p2.x; + const auto y2 = p.y - p2.y; + return (x1 * y2 - x2 * y1 == 0) && (x1 * x2 <= 0) && (y1 * y2 <= 0); +} + +template <typename T> +bool GeometryUtil<T>::segmentIntersectSegment(const Point<T>& a, + const Point<T>& b, + const Point<T>& c, + const Point<T>& d) { + // a, b are end points for line segment1, c and d are end points for line segment2 + const auto perp = [](const Point<T>& v1, const Point<T>& v2) { return (v1.x * v2.y - v1.y * v2.x); }; + + // check if two segments are parallel or not + // precondition is end point a, b is inside polygon, if line a->b is + // parallel to polygon edge c->d, then a->b won't intersect with c->d + auto vectorP = Point<T>(b.x - a.x, b.y - a.y); + auto vectorQ = Point<T>(d.x - c.x, d.y - c.y); + if (perp(vectorQ, vectorP) == 0) return false; + + // check if p1 and p2 are in different sides of line segment q1->q2 + const auto twoSided = [](const Point<T>& p1, const Point<T>& p2, const Point<T>& q1, const Point<T>& q2) { + // q1->p1 (x1, y1), q1->p2 (x2, y2), q1->q2 (x3, y3) + T x1 = p1.x - q1.x; + T y1 = p1.y - q1.y; + T x2 = p2.x - q1.x; + T y2 = p2.y - q1.y; + T x3 = q2.x - q1.x; + T y3 = q2.y - q1.y; + auto ret1 = (x1 * y3 - x3 * y1); + auto ret2 = (x2 * y3 - x3 * y2); + return (ret1 > 0 && ret2 < 0) || (ret1 < 0 && ret2 > 0); + }; + + // If lines are intersecting with each other, the relative location should be: + // a and b lie in different sides of segment c->d + // c and d lie in different sides of segment a->b + return twoSided(a, b, c, d) && twoSided(c, d, a, b); +} + +template <typename T> +bool GeometryUtil<T>::lineIntersectPolygon(const Point<T>& p1, const Point<T>& p2, const Polygon<T>& polygon) { + for (auto ring : polygon) { + auto length = ring.size(); + // loop through every edge of the ring + for (std::size_t i = 0; i < length - 1; ++i) { + if (segmentIntersectSegment(p1, p2, ring[i], ring[i + 1])) { + return true; + } + } + } + return false; +} + +// ray casting algorithm for detecting if point is in polygon +template <typename T> +bool GeometryUtil<T>::pointWithinPolygon(const Point<T>& point, const Polygon<T>& polygon, bool trueOnBoundary) { + bool within = false; + for (const auto& ring : polygon) { + const auto length = ring.size(); + // loop through every edge of the ring + for (std::size_t i = 0; i < length - 1; ++i) { + if (pointOnBoundary(point, ring[i], ring[i + 1])) return trueOnBoundary; + if (rayIntersect(point, ring[i], ring[i + 1])) { + within = !within; + } + } + } + return within; +} + +template <typename T> +bool GeometryUtil<T>::pointWithinPolygons(const Point<T>& point, const MultiPolygon<T>& polygons, bool trueOnBoundary) { + for (const auto& polygon : polygons) { + if (pointWithinPolygon(point, polygon, trueOnBoundary)) return true; + } + return false; +} + +template <typename T> +bool GeometryUtil<T>::lineStringWithinPolygon(const LineString<T>& line, const Polygon<T>& polygon) { + const auto length = line.size(); + // First, check if geometry points of line segments are all inside polygon + for (std::size_t i = 0; i < length; ++i) { + if (!pointWithinPolygon(line[i], polygon)) { + return false; + } + } + + // Second, check if there is line segment intersecting polygon edge + for (std::size_t i = 0; i < length - 1; ++i) { + if (lineIntersectPolygon(line[i], line[i + 1], polygon)) { + return false; + } + } + return true; +} + +template <typename T> +bool GeometryUtil<T>::lineStringWithinPolygons(const LineString<T>& line, const MultiPolygon<T>& polygons) { + for (const auto& polygon : polygons) { + if (lineStringWithinPolygon(line, polygon)) return true; + } + return false; +} + +template struct GeometryUtil<double>; +template struct GeometryUtil<int64_t>; + +} // namespace mbgl |