Point in Polygon including edge cases with margin in c#

Question

I am using Unity3D and I have a polygon (Vector2 array) as well as points to check. For the last few days I was searching for solutions including pnpoly and other algorithms. The problem is I have an inaccuracy of up to 0.001f because I project 3D Faces onto a 2D plane by multiplying with a Quaternion right after using TransformPoint (to get the world position of a mesh-vertex).

I don't know anything about the polygons because they are formed from a number of mesh-triangles - they can have any shape.

How could I deal with this extreme inaccuracy and find all points that are inside or on the boundaries of the polygon?

    public static bool IsInsidePolygon(Vector2[] vertices, Vector2 checkPoint)
    {
        float[] vertX = new float[vertices.Length];
        float[] vertY = new float[vertices.Length];
        for (int i = 0; i < vertices.Length; i++)
        {
            vertX[i] = vertices[i].x;
            vertY[i] = vertices[i].y;
        }

        return IsInsidePolygon(vertices.Length, vertX, vertY, checkPoint.x, checkPoint.y);
    }

    public static bool IsInsidePolygon3(int nvert, float[] vertx, float[] verty, float testx, float testy)
    {
        int i, j = 0;
        bool c = false;
        for (i = 0, j = nvert - 1; i < nvert; j = i++)
        {
            if (((verty[i] > testy) != (verty[j] > testy)) &&
         (testx < (vertx[j] - vertx[i]) * (testy - verty[i]) / (verty[j] - verty[i]) + vertx[i]))
                c = !c;
        }
        return c;
    }

Answer 1

The solution was to find the Closest Distance to the Polygon and return true if the distance is within the margin, here is the whole code:

'''

public static float DistancePointLine2D(Vector2 point, Vector2 lineStart, Vector2 lineEnd)
{
    return (ProjectPointLine2D(point, lineStart, lineEnd) - point).magnitude;
}
public static Vector2 ProjectPointLine2D(Vector2 point, Vector2 lineStart, Vector2 lineEnd)
{
    Vector2 rhs = point - lineStart;
    Vector2 vector2 = lineEnd - lineStart;
    float magnitude = vector2.magnitude;
    Vector2 lhs = vector2;
    if (magnitude > 1E-06f)
    {
        lhs = (Vector2)(lhs / magnitude);
    }
    float num2 = Mathf.Clamp(Vector2.Dot(lhs, rhs), 0f, magnitude);
    return (lineStart + ((Vector2)(lhs * num2)));
}


public static float ClosestDistanceToPolygon(Vector2[] verts, Vector2 point)
{
    int nvert = verts.Length;
    int i, j = 0;
    float minDistance = Mathf.Infinity;
    for (i = 0, j = nvert - 1; i < nvert; j = i++)
    {
        float distance = DistancePointLine2D(point, verts[i], verts[j]);
        minDistance = Mathf.Min(minDistance, distance);
    }

    return minDistance;
}

public static bool IsInsidePolygon(Vector2[] vertices, Vector2 checkPoint, float margin = 0.01f)
{
    if(ClosestDistanceToPolygon(vertices, checkPoint) < margin)
    {
        return true;
    }

    float[] vertX = new float[vertices.Length];
    float[] vertY = new float[vertices.Length];
    for (int i = 0; i < vertices.Length; i++)
    {
        vertX[i] = vertices[i].x;
        vertY[i] = vertices[i].y;
    }

    return IsInsidePolygon(vertices.Length, vertX, vertY, checkPoint.x, checkPoint.y);
}

public static bool IsInsidePolygon(int nvert, float[] vertx, float[] verty, float testx, float testy)
{
    bool c = false;
    int i, j = 0;
    for (i = 0, j = nvert - 1; i < nvert; j = i++)
    {
        if ((((verty[i] <= testy) && (testy < verty[j])) ||

             ((verty[j] <= testy) && (testy < verty[i]))) &&

            (testx < (vertx[j] - vertx[i]) * (testy - verty[i]) / (verty[j] - verty[i]) + vertx[i]))
            c = !c;
    }
    return c;
}

'''