   Collision Detection using lesson 30
  I'm doing a scene using openGL (a house). I want to do some collision detection, mainly with the walls in the house.I have tried using the TestIntersionPlane function in Lesson 30 but I don't understand what exactly should the first two parameters be. I've tried the following:Vector planeNor(0,0,1);Vector position(0,0,-10);Plane p(planeNor,position);Vector vel(0,0,-1);double lamda;Vector pNormal;coll= p.TestIntersionPlane(vel,Z,lamda,pNormal);glPushMatrix();glBegin(GL_QUADS);if(coll)glColor3f(1,0,0);elseglColor3f(1,1,1);glVertex3d(0,0,-10);glVertex3d(3,0,-10);glVertex3d(3,3,-10);glVertex3d(0,3,-10);glEnd();glPopMatrix();where Z is initially (0,0,0) and everytime I move the camera towards the plane, I reduce its z component by 0.1 (i.e. Z.z-=0.1 ).I know that the problem is with the vel vector, but I can't figure out what the right value should be. Can anyone help me please?   