One 、 explain
stay GIS field , It is a basic method to judge whether the point is within the polygon range , Here we mainly talk about the implementation principle .
The principle is simple , There is one GIS theory , A point sends rays in one direction , If the intersection point of the ray and each edge of the polygon is odd, it means that the point is within the scope of the polygon .
( The picture is quoted from ：https://blog.csdn.net/qq_27161673/article/details/52973866)
Two 、 Implementation code
So the implementation code is very clear , Any point creates a ray to the right , Why is the right side , Because the horizontal line can be maintained y unchanged , This situation is the simplest and better understood . The implementation code is as follows ：
// Determine whether the point is within the polygon range
function queryPtInPolygon(point, polygon) {
var p1, p2, p3, p4; p1 = point;
p2 = { x: 1000000000000, y: point.y }; var count = 0;
// Compare each edge to the ray
for (var i = 0; i < polygon.length - 1; i++) {
p3 = polygon[i]; p4 = polygon[i + 1];
if (checkCross(p1, p2, p3, p4) == true) {
count++;
}
}
p3 = polygon[polygon.length - 1]; p4 = polygon[0];
if (checkCross(p1, p2, p3, p4) == true) {
count++;
} return (count % 2 == 0) ? false : true; // Judge whether two line segments intersect
function checkCross(p1, p2, p3, p4) {
var v1 = { x: p1.x - p3.x, y: p1.y - p3.y },
v2 = { x: p2.x - p3.x, y: p2.y - p3.y }, v3 = { x: p4.x - p3.x, y: p4.y - p3.y },
v = crossMul(v1, v3) * crossMul(v2, v3); v1 = { x: p3.x - p1.x, y: p3.y - p1.y };
v2 = { x: p4.x - p1.x, y: p4.y - p1.y }; v3 = { x: p2.x - p1.x, y: p2.y - p1.y };
return (v <= 0 && crossMul(v1, v3) * crossMul(v2, v3) <= 0) ? true : false; } // Calculate the vector cross product
function crossMul(v1, v2) {
return v1.x * v2.y - v1.y * v2.x;
}
}
}
Test case download address ：https://download.csdn.net/download/jiangfei200809/9213835
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