View Full Version : Distance Calculation

07-30-2001, 11:00 PM
How do I calculate the distance between coordinates of a rotated object and eye position ?

I am not the math expert, so please explain with easy formula or codes.

07-31-2001, 04:21 AM
Well i'm not sure i've understood the question, but why don't you use pythagor's formula:
distance between (x1,y1,z1) and (x2,y2,z2)
= sqrt ((x1-x2)*(x1-x2)+((y1-y2)*(y1-y2)+((z1-z2)*(z1-z2))
For the sqrt function, include <math.h>.
I don't see why you talk about a rotated object : rotation preserves distances, so you don't need to take care of rotations when you are computing distances. Good luck !

07-31-2001, 03:49 PM
What I meant was not just rounding the object at its center.

Say I have a cube at (10,10, 0) and rotate 20 degrees around x axis and 30 degrees for z axis centering (100,100,40).
Then what is the distance between cube and me?

07-31-2001, 11:58 PM
I don't know if theres any way to access it but thats the info the Z buffer holds.

Otherwise the previously mentioned distance formula will have to be used. Maybe if you use glLookAt to do the movement of the camera you can then do a distance check to the object, Try doing one to each vertex then take the shortest values as the correct distance.

08-01-2001, 12:50 AM
You have to multiply your object initial coordonates by the modelview matrix. Then you obtain your transformed coordinates. You obtain the distance in one soustraction (eyepos - transformCubePos)

08-01-2001, 10:49 PM
Someone taught me how to solve the problem by using the viewing frustum.

It looked like what I wanted.

Thanks everyone.

08-02-2001, 05:33 AM
Ok... if you know coordinates of your object in the window, you can do gluUnProject to find the object coord BEFORE projection. If you just a depth clamped between 0 and 1, you can readback the depth buffer with glReadPixel.