add project point to plane

src/GShark.Test.XUnit/Geometry/Point3Tests.cs

@@ -57,6 +57,24 @@ public void It_Checks_If_A_Point_Lies_On_A_Plane()
             // Assert
             pt.IsOnPlane(plane, 0.001).Should().BeTrue();
         }
+
+        [Fact]
+        public void If_Check_Project_A_Point_On_A_Plane()
+        {
+            // Arrange
+            Point3 point = new Point3(10, 20, -5);
+            Point3 planeOrigin = new Point3(0, 10, 0);
+            Vector3 direction = new Vector3(0, 1, 0);
+            Plane plane = new Plane(planeOrigin, direction);
+            var expectedPt = new Point3(10, 10, -5);
+
+            // Act
+            var result = Point3.ProjectTo(point,plane);
+
+            // Assert
+            result.Should().BeEquivalentTo(expectedPt);
+            result.Equals(expectedPt).Should().Be(true);
+        }
 
         [Fact]
         public void It_Returns_The_Linear_Interpolation_Between_Two_Points()
@@ -71,6 +89,7 @@ public void It_Returns_The_Linear_Interpolation_Between_Two_Points()
             var result = Point3.Interpolate(p1, p2, amount);
 
             // Assert
+
             result.Equals(expectedPoint).Should().Be(true);
         }
 

src/GShark/Geometry/Point3.cs

@@ -527,6 +527,20 @@ public double DistanceTo(Point3 other)
             }
             return d;
         }
+
+        /// <summary>
+        /// Project a point onto a plane.
+        /// </summary>
+        /// <param name="point">point</param>
+        /// <param name="plane">plane to project onto</param>
+        /// <returns name="the point projected to plane"></returns>
+        public static Point3 ProjectTo(Point3 point, Plane plane)
+        {
+            Vector3 v = plane.Origin - point;
+            Vector3 normal = plane.ZAxis;
+            double d = Vector3.DotProduct(v, normal);
+            return point + d * normal;
+        }
 
         /// <summary>
         /// Calculates the distance of a point to a line.
@@ -665,6 +679,7 @@ public int InPolygon(Polygon polygon)
             }
             return inside ? 1 : -1;
         }
+
     }
 }