How to Determine if a Point Lies Inside a Polygon in C#?

Determining Point Position within a Polygon in C#

When working with polygons, a common task is to determine whether a given point lies within its boundaries. In this article, we will explore how to implement this functionality in C# without relying on external libraries.

Our approach involves two steps:

1. Calculate Outer Bounds:

We first define the outer bounds of the polygon by finding the minimum and maximum X and Y coordinates of its vertices. This helps us quickly determine if the point is within the polygon's bounding box.

2. Check Point Inclusion:

To determine if the point is actually inside the polygon, we use the "IsPointInPolygon" algorithm. This algorithm iterates through the polygon's vertices, checking if the point lies to the left or right of the line connecting each pair of vertices. If the point consistently lies to the same side of these lines, it is determined to be inside the polygon.

Here is an example implementation of the algorithm in C#:

public bool IsPointInPolygon(Point[] polygon, Point point)
{
    bool result = false;
    int j = polygon.Length - 1;
    for (int i = 0; i < polygon.Length; i++)
    {
        if (polygon[i].Y < point.Y && polygon[j].Y >= point.Y || 
            polygon[j].Y < point.Y && polygon[i].Y >= point.Y)
        {
            if (polygon[i].X + (point.Y - polygon[i].Y) /
                (polygon[j].Y - polygon[i].Y) *
                (polygon[j].X - polygon[i].X) < point.X)
            {
                result = !result;
            }
        }
        j = i;
    }
    return result;
}

By following these steps, we can efficiently determine whether a given point is located within a polygon using only C# and WinForms.

The above is the detailed content of How to Determine if a Point Lies Inside a Polygon in C#?. For more information, please follow other related articles on the PHP Chinese website!