a c# helper class that contains the basic geometry operations.

Geometry.cs

using System;
using System.Text;
using System.Windows;

namespace Geometry.NET
{
    public static class Basic
    {
        // a basic struct that represnt a line's equation
        public struct Equation
        {
            public double m;
            public double b;           

            public Equation(double p1, double p2)
            {                
                this.m = p1;
                this.b = p2;
            }
        }

       // convert from radian to degree
        public static double RadianToDegree(double angle)
        {
            return angle * (180.0 / Math.PI);
        }

       // return the angle between two lines
        public static double GetAngle(Point P1 , Point P2 , Point Vertex)
        {
            float f1 = (float)(GetDistanceInPX(Vertex, P1) * GetDistanceInPX(Vertex, P1) + GetDistanceInPX(Vertex, P2) * GetDistanceInPX(Vertex, P2) - GetDistanceInPX(P1, P2) * GetDistanceInPX(P1, P2));
            float f2 = (float)(2 * GetDistanceInPX(Vertex, P1) * GetDistanceInPX(Vertex, P2));
            double r = Math.Acos(f1 / f2);
            return RadianToDegree(r);
        }

        // get an equation from a line
        public static Equation GetEquation(Line L)
        {
            float m = (float)((L.Y2 - L.Y1) / (L.X2 - L.X1));
            float b = (float)(L.Y1 - m * L.X1);            
            return new Equation(m,b);
        }
        // return the intersection point bewteen two lines
        public static Point GetIntersection(Equation E1, Equation E2 )
        {            

            double delta = E2.m - E1.m;
            if (delta == 0)
                throw new ArgumentException("Lines are parallel");
            double x = Double.Parse(((E1.b-E2.b)/delta).ToString("0.00"));
            double y = Double.Parse(((- E1.m * E2.b + E2.m * E1.b) / delta).ToString("0.00"));            
            return new Point(x,y);
        }

        // given the point P , return a new line parallel to L
        public static Equation GetParallelLine(Equation E, Point P)
        {
            double Slope = E.m;
            Equation Parallell = new Equation();
            Parallell.m = Slope;
            Parallell.b = -Slope * P.X + P.Y;
            return Parallell;
        }

        // given a point P , return the perpendicular projection point with the line L
        public static Point GetPIntersection(Line L, Point P)
        {
            Equation E = GetEquation(L);
            double Slope = -1 / E.m;
            Equation Perpendicular = new Equation();
            Perpendicular.m = Slope;
            Perpendicular.b = -Slope * P.X + P.Y;
            Point r = GetIntersection(E, Perpendicular);
            return r;
        }
        
        // return the distance between two points in mm
        public static float GetDistanceInMM(Point P1, Point P2)
        {
            float a = (float)(P1.X - P2.X);
            float b = (float)(P1.Y - P2.Y);
            float distance = (float)(Math.Sqrt(a * a + b * b));
            return (float)(distance * 0.264583333);
        }

        // return the distance between two points in mm
        public static double GetDistanceInPX(Point P1, Point P2)
        {
            double a = (P1.X - P2.X);
            double b = (P1.Y - P2.Y);
            double r = a * a + b * b;
            double distance = Math.Sqrt(r);
            return distance;
        }   
       
        
        // return the percentage of a given value from a whole value
        public static double GetPercentage(float Given, float Whole)
        {
            return Given * 100 / Whole;
        }

        // return the midpoint of a given line
        public static Point GetMidPoint(Point P1 , Point P2)
        {
            double X = Double.Parse(((P1.X + P2.X) / 2).ToString("0.00"));
            double Y = Double.Parse(((P1.Y + P2.Y) / 2).ToString("0.00"));
            return new Point(X,Y);
        }
        
    }
}