MKPolygon面积计算 [英] MKPolygon area calculation
本文介绍了MKPolygon面积计算的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
我正在尝试为MKPolygon制作区域计算类别。
我发现了一些JS代码 https:// github。 com / mapbox / geojson-area / blob / master / index.js#L1 ,带有算法链接: http://trs-new.jpl.nasa.gov/dspace/handle/2014/40409 。
它说:
I'm trying to make an area calculation category for MKPolygon. I found some JS code https://github.com/mapbox/geojson-area/blob/master/index.js#L1 with a link to the algorithm: http://trs-new.jpl.nasa.gov/dspace/handle/2014/40409. It says:
这是我的代码,它给出了错误的结果(比实际数千倍):
Here is my code, which gave a wrong result (thousands times more than actual):
#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?
推荐答案
的最后一步i = N-1
和<$ c循环中缺少$ c> i + 1 = 0 (环绕)。
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