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Dan111 science forum beginner
Joined: 06 Mar 2006
Posts: 20

Posted: Thu Jul 20, 2006 9:33 pm Post subject:
Adding 2 sets of roll/pitch/yaw



Hello,
I have been working on a problem for a day now and am spinning my
wheels. What is the easiest way to add two sets of roll/pitch/yaw
angles? For example, an airplane is at 25deg pitch, 0 deg roll, and a
heading of 90 degrees, and the pilot is wearing a head mounted display
that is independent of the airframe.
Tried transformation matricies and couldn't quite get it right. I
thought there may be an easier solution.
Any help would really be great!
Thanks,
Dan Hoffard 

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matt271829news@yahoo.co. science forum Guru
Joined: 11 Sep 2005
Posts: 846

Posted: Fri Jul 21, 2006 10:39 am Post subject:
Re: Adding 2 sets of roll/pitch/yaw



Dan wrote:
Quote:  Hello,
I have been working on a problem for a day now and am spinning my
wheels. What is the easiest way to add two sets of roll/pitch/yaw
angles? For example, an airplane is at 25deg pitch, 0 deg roll, and a
heading of 90 degrees, and the pilot is wearing a head mounted display
that is independent of the airframe.
Tried transformation matricies and couldn't quite get it right. I
thought there may be an easier solution.
Any help would really be great!
Thanks,
Dan Hoffard

I was going to have a go at working this out, then I realised that I'm
not completely clear how pitch, roll and yaw are successively applied
to determine the attitude of the aircraft (let's assume it's an
aircraft).
This is the (to me) obvious method:
1. Set up appropriate xyz axes, which remain fixed throughout (e.g. x
axis pointing north, y axis pointing east, z axis pointing vertically
upwards).
2. Initially position the aircraft with the tail lying on the negative
x axis, the nose lying on the positive x axis, the left wingtip on the
negative y axis and the right wingtip on the positive y axis.
3. Rotate the aircaft through the pitch angle about the y axis.
4. Rotate the aircraft through the yaw angle about the z axis.
5. Rotate the aircraft through the roll angle about its own axis.
We would also need to know the convention for the direction in which
angles are measured (i.e. whether a positive angle is clockwise or
anticlockwise when looking along the axis in the positive direction).
But some sources are very vague about the order in which these
operations are applied, and the axes about which rotation takes place
(for example, whether the yaw angle is about the original z axis, or
about a new z axis perpendicular to the plane of nosetailwingtips
after pitch has been applied). What's your interpretation?
Once the aircraft's attitude is determined, I assume we set up new
x'y'z' axes, with the x'axis pointing from tail to nose, the y' axis
pointing from left wingtip to right wingtip, and the z' axis orthogonal
to both these and pointing from the underside of the aircraft through
the top side of the aircraft. Then a new pitch, roll, yaw is applied
relative to this new axis system, and you want the resultant pitch,
roll, yaw relative to the original xyz coordinate system. Is that
right? 

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