
Hi Objo and everybody,
First of all I want to congratulate you for this great Helix 3D tookit
I had to use one of the methods of class BoundingSphere and as it was not implemented so I did it. Feel free to test and include the code I'm sending here.
Best Regards,
Rui
public bool RayIntersection(Ray3D ray, out Point3D[] result)
{
result = null;
bool inter = false;
double h = this.center.X ;
double j = this.center.Y;
double k = this.center.Z;
double ra = this.radius;
double x1 = ray.Origin.X ;
double y1 = ray.Origin.Y;
double z1 = ray.Origin.Z;
double a = x1  ray.Origin.X * ray.Direction.X;
double b = y1  ray.Origin.Y * ray.Direction.Y;
double c = z1  ray.Origin.Z * ray.Direction.Z;
//Quadratic solving
double aQ = a * a + b * b + c * c;
double bQ = 2 * a * (x1  h) + 2 * b * (y1  j) + 2 * c * (z1  k);
double cQ = x1 * x1 + y1 * y1 + z1 * z1 + h * h + k * k + j * j  2 * (j * y1 + k * z1 + h * x1)  ra * ra;
//Dscriminant
double Q = bQ * bQ  4 * aQ * cQ;
if (Q >= 0)
{
double rx1 = (bQ + Math.Sqrt(bQ * bQ  4 * aQ * cQ)) / (2 * aQ); //First Root
double rx2 = (bQ  Math.Sqrt(bQ * bQ  4 * aQ * cQ)) / (2 * aQ); //Second Root
//first Intersection
Point3D I1 = new Point3D(x1 + a * rx1,y1 + b * rx1 , z1 + c * rx1);
//Second Intersection
Point3D I2 = new Point3D(x1 + a * rx2, y1 + b * rx2, z1 + c * rx2);
//ray inside sphere
if ((ray.Origin  this.center).Length <= this.radius)
{
result = new Point3D[1];
//Check if the vectors have the same direction
if (Vector3D.DotProduct(ray.Direction, I1  ray.Origin) >= 0)
{
result[0] = I1;
}
else
{
result[0] = I2;
}
}
else
{
result = new Point3D[2];
result[0] = I1;
result[1] = I2;
}
inter = true;
}
else
{
inter = false;
}
return inter;
}



thanks for the code! Did you make this yourself, or do you have a reference?
I created some unit tests for this code, but could not get my last case (no intersection) to work:
[Test, Ignore]
public void RayInterSection_NoIntersections()
{
var ray = new Ray3D(new Point3D(0.2, 0.3, 1), new Vector3D(1, 0.1, 0.1));
var sphere = new BoundingSphere(new Point3D(0.2, 0.3, 0), 1.0);
Point3D[] result;
Assert.IsFalse(sphere.RayIntersection(ray, out result));
Assert.AreEqual(sphere.Radius, sphere.Center.DistanceTo(result[0]), 1e6, "Point is not on sphere.");
Assert.AreEqual(0, ray.GetNearest(result[0]).DistanceTo(result[0]), 1e6, "Point is not on ray.");
}



Hi objo,
I did the all code myself, and yes I have some references from Wikipedia and other common links that I will give.
I'm also finishing a detailed presentation with the all
theoretical stuff, and I will post it all here.
Regards,
Rui



Hi Objo,
I've made some improvements, and you can find the new code below. I'm also posting some test cases. (I've changed your "no intersections" case )
You can also find my detailed explanation and references
here
thanks,
Rui
public bool RayIntersection(Ray3D ray, out Point3D[] result)
{
result = new Point3D[2];
result[0] = new Point3D(double.PositiveInfinity, double.PositiveInfinity, double.PositiveInfinity);
result[1] = new Point3D(double.PositiveInfinity, double.PositiveInfinity, double.PositiveInfinity);
bool inter = false;
double h = this.center.X;
double j = this.center.Y;
double k = this.center.Z;
double ra = this.radius;
double x1 = ray.Origin.X;
double y1 = ray.Origin.Y;
double z1 = ray.Origin.Z;
//[a,b,c] = Ray.direction
double a = ray.Direction.X;
double b = ray.Direction.Y;
double c = ray.Direction.Z;
//Quadratic solving
double aQ = a * a + b * b + c * c;
double bQ = 2 * a * (x1  h) + 2 * b * (y1  j) + 2 * c * (z1  k);
double cQ = x1 * x1 + y1 * y1 + z1 * z1 + h * h + k * k + j * j  2 * (j * y1 + k * z1 + h * x1)  ra * ra;
//Dscriminant
double Q = bQ * bQ  4 * aQ * cQ;
if (Q >= 0) //We have at least one possible Intersection
{
double rx1 = (bQ + Math.Sqrt(bQ * bQ  4 * aQ * cQ)) / (2 * aQ); //First Root
double rx2 = (bQ  Math.Sqrt(bQ * bQ  4 * aQ * cQ)) / (2 * aQ); //Second Root
//first Possible Intersection
Point3D I1 = new Point3D(x1 + a * rx1, y1 + b * rx1, z1 + c * rx1);
//Second Possible Intersection
Point3D I2 = new Point3D(x1 + a * rx2, y1 + b * rx2, z1 + c * rx2);
//Check if I1 is intersection by laying in the ray
if (Vector3D.DotProduct(ray.Direction, I1  ray.Origin) >= 0)
{
result[0] = I1;
inter = true;
}
//Check if I2 is intersection by laying in the ray
if (Vector3D.DotProduct(ray.Direction, I2  ray.Origin) >= 0)
{
result[1] = I2;
inter = true;
}
}
return inter;
}
TESTS:
[Test]
public void RayInterSection_HasIntersections()
{
var ray = new Ray3D(new Point3D(0.2, 0.3, 0), new Vector3D(1, 0, 0));
var sphere = new BoundingSphere(new Point3D(0.2, 0.3, 0), 1.0);
Point3D[] result;
Assert.IsTrue(sphere.RayIntersection(ray, out result));
Assert.AreEqual(sphere.Radius, sphere.Center.DistanceTo(result[0]), 1e6, "Point is not on sphere.");
Assert.AreEqual(0, ray.GetNearest(result[0]).DistanceTo(result[0]), 1e6, "Point "+ result[0] +" is not on ray.");
}
[Test]
public void RayInterSection_NoIntersections()
{
var ray = new Ray3D(new Point3D(0.2, 0.3, 1), new Vector3D(1, 0.1, 0.1));
var sphere = new BoundingSphere(new Point3D(0.2, 0.3, 0), 1.0);
Point3D[] result;
Assert.IsFalse(sphere.RayIntersection(ray, out result));
Assert.IsTrue( double.IsInfinity(sphere.Center.DistanceTo(result[0])), "There is a finite solution 1.");
Assert.AreNotEqual(0, ray.GetNearest(result[0]).DistanceTo(result[0]), "Point 1 is on ray.");
Assert.IsTrue(double.IsInfinity(sphere.Center.DistanceTo(result[1])), "There is a finite solution 2.");
Assert.AreNotEqual(0, ray.GetNearest(result[0]).DistanceTo(result[1]), "Point 2 is on ray.");
}
[Test]
public void RayInterSection_TwoIntersections()
{
var sphere = new BoundingSphere(new Point3D(0.2, 0.3, 0), 1.0);
var ray = new Ray3D(new Point3D(12, 23, 32), sphere.Center  new Point3D(12, 23, 32)); // vector away and pointing to the center of sphere
Point3D[] result;
Assert.IsTrue(sphere.RayIntersection(ray, out result));
Assert.AreEqual(sphere.Radius, sphere.Center.DistanceTo(result[0]), 1e6, "Point 1 is not on sphere.");
Assert.AreEqual(0, ray.GetNearest(result[0]).DistanceTo(result[0]), 1e6, "Point 1" + result[0] + " is not on ray.");
Assert.AreEqual(sphere.Radius, sphere.Center.DistanceTo(result[1]), 1e6, "Point 2 is not on sphere.");
Assert.AreEqual(0, ray.GetNearest(result[1]).DistanceTo(result[1]), 1e6, "Point 2 " + result[0] + " is not on ray.");
}
[Test]
public void RayInterSection_OnlyOneIntersection()
{
var sphere = new BoundingSphere(new Point3D(0.2, 0.3, 0), 1.0);
var ray = new Ray3D(sphere.Center, new Vector3D(1, 0.1, 0.1)); // vector origin in the center of sphere pointing away
Point3D[] result;
Assert.IsTrue(sphere.RayIntersection(ray, out result), "No intersection");
Assert.IsTrue(sphere.Center.DistanceTo(ray.Origin ) <= sphere.Radius,"Ray origin outside sphere");
Assert.IsFalse( double.IsInfinity(sphere.Center.DistanceTo(result[0])) && double.IsInfinity(sphere.Center.DistanceTo(result[1])), "No Intersections");
Assert.IsFalse(!double.IsInfinity(sphere.Center.DistanceTo(result[0])) && !double.IsInfinity(sphere.Center.DistanceTo(result[1])), "Two Intersections");
}
[Test]
public void RayInterSection_TwoTangentIntersections()
{
var sphere = new BoundingSphere(new Point3D(0.2, 0.3, 0), 1.0);
var ray = new Ray3D(new Point3D(sphere.Center.X + sphere.Radius, sphere.Center.Y + sphere.Radius, sphere.Center.Z + 50), new Point3D(sphere.Center.X + sphere.Radius, sphere.Center.Y, sphere.Center.Z)  new Point3D(sphere.Center.X + sphere.Radius, sphere.Center.Y + sphere.Radius, sphere.Center.Z + 50)); // ray tangent to sphere
Point3D[] result;
Assert.IsTrue(sphere.RayIntersection(ray, out result), "No intersection");
Assert.IsTrue(!double.IsInfinity(sphere.Center.DistanceTo(result[0])) && !double.IsInfinity(sphere.Center.DistanceTo(result[1])), "Less then two Intersections");
Assert.IsTrue(result[0]==result[1], "Solutions are not equal");
}



thanks for the unit tests. I have done some modifications and submitted the changes!

