How to calculate the distance between two in 3D (x1,y1,z1) & (x2,y2,z2) ?? Sorry about my math, I know how to do it in 2D, is it the same ?? Can I use vector operation (dot, cross, multiply) to do it ?? what exactly does dot, cross, mul mean (I mean how to implement in solving problem)?? Thanks

If I''m not mistaken, you can use this:

Distance = sqrt((x1-x2)^2 + (y1-y2)^2 + (z1-z2)^2)

correct.

subtracting one point from the other gives you a vector that is the length of the distance between the points.

then you use basically 3D pythagorean theorem as per the equation above.

-me

Hmm.. assuming that I have 2 bounding circles .. errr.. balls with radius r1 and r2..
how can I check if those two collided or not ?
The idea is =
if (sqr(x1-x2)+sqr(y1-y2)+sqr(z1-z2) < sqr(r1)+sqr(r2)) then
collided
else
not collided
??? is it true ?? Can somebody explain the theory behind those equation ??

umm...

do not use a square root - keep the values squared

Your comparison is incorrect. The correct comparison is

length(c2 - c1) < r1 + r2

which expands to (if you eliminate the square roots)

(x2 - x1)² + (y2 - y1)² + (z2 - z1)² < (r1 + r2)²

Cédric