Checking if a point is inside a polygon is RIDICULOUSLY simple (Ray casting algorithm) - Inside code
Why Stack Overflow recommends it
Stack Overflow users link it when answering or debugging point-in-polygon questions, since it explains the even-odd ray casting rule and its edge cases clearly.
Recommended by 2 people across 2 different months, 2023 to 2024.
What it is
A six-minute explainer from the Inside code channel that shows how the ray casting algorithm decides whether a point lies inside a polygon. It walks through counting edge crossings of a ray from the point and gives accompanying source code in a linked gist.
What people said
Recommends Lurchfresser · 2024-04 · Stack Overflow · on “google maps flutter check if a point inside a polygon”
I stumbled upon this post because i wanted to solve a similar problem in my code. Unfortunatly both of the answers miss one edgecase, as well as the flutter point in poly library [LINK] . If on edge is a vertical edge, m will be Infinity. This can be avoided by also checking, if the point is to the west (or "left") of both points of the edges, because that condition will always be true for a vertical edge. This also improves performance. For fully understanding this problem I recommend this [this video] video. Improved Code: class Point { Point({required this.x, required this.y}); /// X axis coordinate or longitude double x; /// Y axis coordinate or latitude double y; } class Poly { /// Check if
Recommends mtanksl · 2024-08 · Stack Overflow · on “How can I determine whether a 2D Point is within a Polygon?”
This Youtube video "Checking if a point is inside a polygon is RIDICULOUSLY simple (Ray casting algorithm) - Inside code" explains the formula used here: [this video]
Cites Zenz · 2023-12 · Stack Overflow · on “Point-In-Polygon boundary inclusive/exclusive”
I'm trying to solve the point-in-polygon problem but I'm facing a problem where the lower bounds of the polygon are not included but the higher bounds do. I've been following the tutorial of inside code [this video] to determine if a point lies within the boundaries of a polygon which uses raycasting and counts if said point is crossing the contour (un)even times to determine if the point lies outside or inside the polygon. This is achieved by checking 2 conditions. One condition for the Y coordinate and the other for the X coordinate looping over each edge of the polygon. In example below I'm using a polygon which is a square with size 3X3. I'm looping over all the coordinates to check if they a
Cites Onki Hara · 2024-05 · Stack Overflow · on “Find point inside polygon”
A rather simple method is computing a raycast from your example point in some direction and count the number of intersections with the edges of your polygon. If the raycast intesects odd-times, the example point is in the polygon, if it intersects even-times then it is outside. A detailed explanation and python sample code can be found here: [this video] One edge case: if the intesection lies exactly on an edge of the polygon you have to decide if its in or out and reflect this case in your code.