检查选定区域中的坐标 [英] Check if coordinate in selected area

问题描述

我有 4 个区域坐标:x1,y1 ...等等.还有一个位置 x0,y0.

I have 4 coordinates of area: x1,y1 ... etc. And have one more position x0,y0.

如何检查我的坐标是否在选定区域?

How to check if my coordinate in selected area?

推荐答案

我将向您解释如何检查 (x0,y0) 是否位于通过 (x1,y1) 和 (x2,y2) 的线下方".本质上，您希望向量 (x0-x1,y0-y1) 指向 (x2-x1, y2-y1) 的右侧".这相当于说矩阵

I will explain you how to check that (x0,y0) lies "below" the line through (x1,y1) and (x2,y2). Essentially, you want that the vector (x0-x1,y0-y1) points "to the right" of (x2-x1, y2-y1). This is equivalent to saying that the matrix

x0-x1      y0-y1

x2-x1      y2-y1

有一个负决定因素.所以你的情况变成了

has a negative determinant. So your condition becomes

(x0-x1)(y2-y1) < (y0-y1)(x2-x1).

对于包围该区域的任何线，您都会得到这样的条件.

You get such a condition for any line bounding the area.

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