I have built a frustum class and been happily testing it and all has been fine, Until now. I seem to get problems for objects that are not at (0,0,0) World space. The thing is I am passing in the location of objects I wish to test and the tests should take this into account. I am calculating the plains like this!! l_FrustumMatrix = (m_View * m_Projection); //Left m_FrustumSide[5].A = l_FrustumMatrix.M14 + l_FrustumMatrix.M11; m_FrustumSide[5].B = l_FrustumMatrix.M24 + l_FrustumMatrix.M21; m_FrustumSide[5].C = l_FrustumMatrix.M34 + l_FrustumMatrix.M31; m_FrustumSide[5].D = l_FrustumMatrix.M44 + l_FrustumMatrix.M41; //Right m_FrustumSide[4].A = l_FrustumMatrix.M14 - l_FrustumMatrix.M11; m_FrustumSide[4].B = l_FrustumMatrix.M24 - l_FrustumMatrix.M21; m_FrustumSide[4].C = l_FrustumMatrix.M34 - l_FrustumMatrix.M31; m_FrustumSide[4].D = l_FrustumMatrix.M44 - l_FrustumMatrix.M41; //Bottom m_FrustumSide[3].A = l_FrustumMatrix.M14 + l_FrustumMatrix.M12; m_FrustumSide[3].B = l_FrustumMatrix.M24 + l_FrustumMatrix.M22; m_FrustumSide[3].C = l_FrustumMatrix.M34 + l_FrustumMatrix.M32; m_FrustumSide[3].D = l_FrustumMatrix.M44 + l_FrustumMatrix.M42; //Top m_FrustumSide[2].A = l_FrustumMatrix.M14 - l_FrustumMatrix.M12; m_FrustumSide[2].B = l_FrustumMatrix.M24 - l_FrustumMatrix.M22; m_FrustumSide[2].C = l_FrustumMatrix.M34 - l_FrustumMatrix.M32; m_FrustumSide[2].D = l_FrustumMatrix.M44 - l_FrustumMatrix.M42; //Near m_FrustumSide[1].A = l_FrustumMatrix.M13; m_FrustumSide[1].B = l_FrustumMatrix.M23; m_FrustumSide[1].C = l_FrustumMatrix.M33; m_FrustumSide[1].D = l_FrustumMatrix.M43; //Far m_FrustumSide[0].A = l_FrustumMatrix.M14 - l_FrustumMatrix.M13; m_FrustumSide[0].B = l_FrustumMatrix.M24 - l_FrustumMatrix.M23; m_FrustumSide[0].C = l_FrustumMatrix.M34 - l_FrustumMatrix.M33; m_FrustumSide[0].D = l_FrustumMatrix.M44 - l_FrustumMatrix.M43; for (l_Index = 0;l_Index < 6;l_Index ++){ m_FrustumSide[l_Index].Normalize(); } And the Visibility test like this!! public Proximity TestSphere(Vector3 p_Centre,Single p_Radius){ Single l_Distance; Int32 l_Index; for (l_Index = 0;l_Index < 6;l_Index ++){ l_Distance = m_FrustumSide[l_Index].Dot(p_Centre) + m_FrustumSide[l_Index].D; if (l_Distance < -p_Radius){ return Proximity.Outside; }else if (Math.Abs(l_Distance) < p_Radius){ return Proximity.Intersecting; } } return Proximity.Inside; } Just to reiterate this all works when the centre of the object is (0,0,0) No matter where the view points to etc. Thanks in advance for any help

I've got a couple of ideas, but first:

1. Could you put the code in [ source ] [ /source ] tags? It's hard to read without indentation.

2. Perhaps you could also post the 'frustum side' class, in particular the 'dot' function.

Sure, now i know the tags (:

There is no code for the Dot function.. its c# directx 9
and FrustumSide is an array of plains.

I'd have to consult the DirectX docs to say for sure, but I'm going to venture a guess. Try changing this:

l_Distance = m_FrustumSide[l_Index].Dot(p_Centre) + m_FrustumSide[l_Index].D;

To:

l_Distance = m_FrustumSide[l_Index].Dot(p_Centre);

I'm thinking that plane.Dot(Vector3) may be of the form:

ax+by+cz+d

And that therefore you don't need to add m_FrustumSide[l_Index].D yourself (and that's what's throwing things off).

Again, without consulting the DirectX docs, this is just a guess on my part.

you are correct.

Your sugestion that the dot may be incorrect made me try

l_Distance = m_FrustumSide[l_Index].A * p_Centre.X + m_FrustumSide[l_Index].B * p_Centre.Y + m_FrustumSide[l_Index].C * p_Centre.Z + m_FrustumSide[l_Index].D;

insted of using the .Dot method.

However leaving the D part of also works!! (: (: