**comp.graphics.algorithms**

## Subject: **Re: Lineal algebra problem**

Thanks, I will try that method.

I am learning Renderman and having problems specifying the camera. It

uses a left-handed system and it seems the camera is fixed and the

"world" system is placed relative to the camera (and not vice versa).

cr88192 wrote:

> "guanaco"

> news:1145235014.461387.155400@z34g2000cwc.googlegroups.com...

> > Hi, I am having problems with transformation matrices. Suppose the

> > camera is in the origin (0 0 0) and pointing to positive "z" (0 0 1).

> > Positive "x" is at the right and positive "y" is up. I need to move the

> > camera to a point P1 (the look-from) pointing to another point P2 (the

> > look-to). Is there a general procedure to do this with translations and

> > rotations?

> >

> thought it was in the faq, but I don't know...

>

> general approach:

> move the camera to P1;

> point the camera at P2.

>

> there is a vector from P1 to P2, which can be useful here.

>

> D=((P2-P1)/|P2-P1|)

> th=atan2(D.x, D.z)

> r=asin(D.y)

>

> where th is yaw and r is pitch (note, in c at least these functions return

> the result in radians, which may or may not be what is desired).

>

> then again, there are alternate definitions of camera orientation, so I gave

> angles. likewise, you didn't specify a lot of things, so likely you will

> need to fudge out the rest on your own.

>

>

> likewise, whether or not it was intentional, the space described is left

> handed (in my experience right handed systems are more common).

> eg:

> opengl will leave you looking in the -Z direction by default (X right, Y

> up);

> most 3D engines I have seen have Z up, X right, and Y forwards;

> ...

>

> but these are right handed spaces.

>

> > Thanks

> >

Reply

View All Messages in

**comp.graphics.algorithms**

path:

Lineal algebra problem =>Re: Lineal algebra problem =>

Replies:

Re: Lineal algebra problem

Copyright © 2006 WatermarkFactory.com. All Rights Reserved.