using System;

using System.IO;

using UnitsNet;

public class Program

{

    public static void Main()

    {

        var coordinates = new [] {

            new Coordinate(0, 12, 0),

            new Coordinate(5, 12, 0),

            new Coordinate(5, 12, 3.6),

            new Coordinate(0, 12, 3.6)

        };

        //Area result = Area.Zero;

        double result = 0D;

        for(int index = 0; index < coordinates.Length; index++) {

            Coordinate current = coordinates[index];

            Coordinate next = coordinates[(index + 1 == coordinates.Length ? 0 : index+1)];

            Coordinate crossProduct = current.CrossProduct(next);

            result += crossProduct.Size();

        }

        Area finalResult = Area.FromSquareMeters(result / 2);

        Console.WriteLine($"Calculated area: {finalResult}");

    }

}

​

public class Coordinate

{

    public Coordinate(double x, double y, double z)

    {

        X = Length.FromMeters(x);

        Y = Length.FromMeters(y);

        Z = Length.FromMeters(z);

    }

    public Coordinate(Length x, Length y, Length z){

        X = x;

        Y = y;

        Z = z;

    }

    public Length X {get;set;}

    public Length Y {get;set;}

    public Length Z {get;set;}

    public Coordinate CrossProduct(Coordinate other){

        var x = (this.Y.Meters * other.Z.Meters) - (this.Z.Meters * other.Y.Meters);

        var y = (this.Z.Meters * other.X.Meters) - (this.X.Meters * other.Z.Meters);

        var z = (this.X.Meters * other.Y.Meters) - (this.Y.Meters * other.X.Meters);

        return new Coordinate(x,y,z);

    }

    public double Size()

    {

        return Math.Sqrt(Math.Pow(this.X.Meters, 2) + Math.Pow(this.Y.Meters, 2) + Math.Pow(this.Z.Meters, 2));

    }

}

​

​