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Fixed centroid computation

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This commit is contained in:
Martin Tůma 2023-02-19 14:47:57 +01:00
parent 8a9b7dc7ec
commit 9538d15d79
1 changed files with 14 additions and 10 deletions
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24
src/map/ENC/rastertile.cpp
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@ -59,10 +59,11 @@ static double area(const QVector<Coordinates> &polygon)
{ {
double area = 0; double area = 0;
for (int i = 0; i < polygon.size(); i++) { for (int i = 0; i < polygon.size() - 1; i++) {
int j = (i + 1) % polygon.size(); const Coordinates &pi = polygon.at(i);
area += polygon.at(i).lon() * polygon.at(j).lat(); const Coordinates &pj = polygon.at(i+1);
area -= polygon.at(i).lat() * polygon.at(j).lon(); area += pi.lon() * pj.lat();
area -= pi.lat() * pj.lon();
} }
area /= 2.0; area /= 2.0;
@ -71,15 +72,18 @@ static double area(const QVector<Coordinates> &polygon)
static Coordinates centroid(const QVector<Coordinates> &polygon) static Coordinates centroid(const QVector<Coordinates> &polygon)
{ {
Q_ASSERT(polygon.size() > 3);
Q_ASSERT(polygon.first() == polygon.last());
double cx = 0, cy = 0; double cx = 0, cy = 0;
double factor = 1.0 / (6.0 * area(polygon)); double factor = 1.0 / (6.0 * area(polygon));
for (int i = 0; i < polygon.size(); i++) { for (int i = 0; i < polygon.size() - 1; i++) {
int j = (i + 1) % polygon.size(); const Coordinates &pi = polygon.at(i);
qreal f = (polygon.at(i).lon() * polygon.at(j).lat() const Coordinates &pj = polygon.at(i+1);
- polygon.at(j).lon() * polygon.at(i).lat()); double f = (pi.lon() * pj.lat() - pj.lon() * pi.lat());
cx += (polygon.at(i).lon() + polygon.at(j).lon()) * f; cx += (pi.lon() + pj.lon()) * f;
cy += (polygon.at(i).lat() + polygon.at(j).lat()) * f; cy += (pi.lat() + pj.lat()) * f;
} }
return Coordinates(cx * factor, cy * factor); return Coordinates(cx * factor, cy * factor);