我正在尝试为MKPolygon创建一个面积计算分类。我发现了一些JS代码https://github.com/mapbox/geojson-area/blob/master/index.js#L1,其中包含到算法的链接:http://trs-new.jpl.nasa.gov/dspace/handle/2014/40409。
它说:
![enter image description here](https://istack.dev59.com/vift6.webp)
这是我的代码,结果错误(比实际面积大数千倍):
#define kEarthRadius 6378137
@implementation MKPolygon (AreaCalculation)
- (double) area {
double area = 0;
NSArray *coords = [self coordinates];
if (coords.count > 2) {
CLLocationCoordinate2D p1, p2;
for (int i = 0; i < coords.count - 1; i++) {
p1 = [coords[i] MKCoordinateValue];
p2 = [coords[i + 1] MKCoordinateValue];
area += degreesToRadians(p2.longitude - p1.longitude) * (2 + sinf(degreesToRadians(p1.latitude)) + sinf(degreesToRadians(p2.latitude)));
}
area = area * kEarthRadius * kEarthRadius / 2;
}
return area;
}
- (NSArray *)coordinates {
NSMutableArray *points = [NSMutableArray arrayWithCapacity:self.pointCount];
for (int i = 0; i < self.pointCount; i++) {
MKMapPoint *point = &self.points[i];
[points addObject:[NSValue valueWithMKCoordinate:MKCoordinateForMapPoint(* point)]];
}
return points.copy;
}
double degreesToRadians(double radius) {
return radius * M_PI / 180;
}
@end
我错过了什么?
i == N-1
和i+1 == 0
(环绕)的最后一步。 - Martin R