Path: chuka.playstation.co.uk!news
From: "Martin Keates" <martin@jabadaw.fsnet.co.uk>
Newsgroups: scee.yaroze.programming.3d_graphics
Subject: Re: libps - RotMatrix()
Date: Fri, 26 Oct 2001 14:31:27 +0100
Organization: PlayStation Net Yaroze (SCEE)
Lines: 35
Message-ID: <9rbol5$2i3@www.netyaroze-europe.com>
References: <3BD923D9.872FC1A0@127.0.0.1>
NNTP-Posting-Host: modem-794.abra.dialup.pol.co.uk
X-Priority: 3
X-MSMail-Priority: Normal
X-Newsreader: Microsoft Outlook Express 5.50.4133.2400
X-MimeOLE: Produced By Microsoft MimeOLE V5.50.4133.2400

> x = banking angle
> y = pitch
> z = direction
>
> so the planes have +ve z as up, and fly in the direction of the +ve y

That makes y roll not pitch, and x,y,z is basically pitch, roll and yaw.

> RotMatrixX(x, mtrx);
> RotMatrixY(y, mtrx);
> RotMatrixZ(z, mtrx);

This is not quite right. For example, if a plane pitches 45 degrees
up and rolls 90 degrees right it will be pointing between the x and
y axes, but its direction of travel will be along the y axis. You need
to swap the x and y rotations (or make your planes point along the
x axis and travel along +ve x) - it's not known as "roll, pitch and yaw"
for nothing. :)

Also, you need to make sure you keep your rotations within a
suitable range. Anything for roll and yaw, but pitch needs to be
within -90 to 90 degrees.

I don't think you'll get any sort of Gimbal Lock problem here. When
pitch is +/- 90 degrees the plane will be vertical so you probably
won't want it to be moving along the y axis. But it should have the
correct orientation. Presumably you move the planes on the
z-axis as well as the y-axis depending on their pitch. You could
get the direction vector of the plane by putting (0,1,0) through the
rotation matrix.

Martin.