问题描述
如何从多个地理位置(长,纬度值)创建多边形地理栅栏。还有如何跟踪用户进入到这个区域范围设定的区域或该区域在Android上退出。
How to create Polygon Geofence from multiple geo locations(long,lat values) . Also how to track user is entering into this geofence region or exiting from this region on android.
推荐答案
一个地理围栏仅仅是形成多边形纬度/长点的数组。一旦你有纬度/长点的列表,你可以用一个点内的多边形检查,看是否有位置是多边形内。
A geofence is simply an array of lat/long points that form a polygon. Once you have a list of lat/long points, you can use a point-inside-polygon check to see if a location is within the polygon.
这是code我在自己的项目来执行点的多边形检查非常大的凹多边形(20K +顶点):
This is code I have used in my own projects to perform point-in-polygon checks for very large concave polygons (20K+ vertices):
public class PolygonTest
{
class LatLng
{
double Latitude;
double Longitude;
LatLng(double lat, double lon)
{
Latitude = lat;
Longitude = lon;
}
}
bool PointIsInRegion(double x, double y, LatLng[] thePath)
{
int crossings = 0;
LatLng point = new LatLng (x, y);
int count = thePath.length;
// for each edge
for (var i=0; i < count; i++)
{
var a = thePath [i];
var j = i + 1;
if (j >= count)
{
j = 0;
}
var b = thePath [j];
if (RayCrossesSegment(point, a, b))
{
crossings++;
}
}
// odd number of crossings?
return (crossings % 2 == 1);
}
bool RayCrossesSegment(LatLng point, LatLng a, LatLng b)
{
var px = point.Longitude;
var py = point.Latitude;
var ax = a.Longitude;
var ay = a.Latitude;
var bx = b.Longitude;
var by = b.Latitude;
if (ay > by)
{
ax = b.Longitude;
ay = b.Latitude;
bx = a.Longitude;
by = a.Latitude;
}
// alter longitude to cater for 180 degree crossings
if (px < 0) { px += 360; };
if (ax < 0) { ax += 360; };
if (bx < 0) { bx += 360; };
if (py == ay || py == by) py += 0.00000001;
if ((py > by || py < ay) || (px > Math.max(ax, bx))) return false;
if (px < Math.min(ax, bx)) return true;
var red = (ax != bx) ? ((by - ay) / (bx - ax)) : float.MAX_VALUE;
var blue = (ax != px) ? ((py - ay) / (px - ax)) : float.MAX_VALUE;
return (blue >= red);
}
}
我会尽力追捕链接到原来的javascript code,我移植这个距离。
I'll try to hunt down the link to the original javascript code that I ported this from.
在程序流程方面,你会希望有一个后台服务做位置更新,然后执行对你的纬度/经度的多边形数据此检查,看是否该位置是内在的。
In terms of program flow, you will want a background service to do location updates and then perform this check against your lat/long polygon data to see if the location is inside.
祝你好运!
编辑:这里是链接到原始出处code,该算法来自:的
Here is the link to the original source code that this algorithm came from:http://www.counsellingbyabhi.com/2013/01/google-map-check-whether-point-latlong.html
这篇关于Android的地理围栏(多边形)的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持!