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From: Lewis_Evans@Playstation.sony.com
Newsgroups: scee.yaroze.programming.3d_graphics
Subject: Matrix Problems
Date: 20 Nov 1997 18:01:44 -0000
Organization: Sony Computer Entertainment Europe - 119.SS5
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From: Lewis_Evans@Playstation.sony.com
To: news@playstation.co.uk


Here is a problem for the mathematicians among you.
If I have 2 objects each with their own coordinate matrix, and I want
them to orient towards each other, how do I do it? I can calculate the
angles between them on the 3 axes, but then I presume its not as
simple as doing a linear interpolation of the matrices because
mathematically that just doesn't look right...
Ideas?


If you want them each to turn to point towards the other, this can be
achieved by each doing the same thing
concurrently.

Eg for 2 ships A and B, consider A first; express the world position of B
in A's local coordinate system,
and then make A rotate around its own axis until B is 'dead ahead' ie the
position of B in A's coordinate space
is (close to ) a vector (0, 0, k). If each does this concurrently, they'll
end up looking right at each other.

Making them fully aligned (so that they both agree where up is) is just
about each doing theta-Z rotation
until their y-axes agree (are the same in world coordinate space).

In the SCEE demo 'flying', some of the later tutoN programs show enemy
ships that turn towards you and fire
at you; they use this method.

     Lewis