[osg-users] How to rotate node's local coordinate system?

Sebastian Messerschmidt sebastian.messerschmidt at gmx.de
Tue Jun 23 03:01:09 PDT 2015

Hi Elias,

Seems like you are after a change of coordinate frame (e.g. which axis 
is front/up etc.)
 From my experience: don't ...
What I usually do ist to transform at the interface by using a 
permutation matrix.
So for instance if you want
x = x´
y = -z
z = y

then multiply your incoming positions/orientation with the matrix
1  0  0  0
0  0 -1  0
0  1  0  0
0  0  0  1

and your outgoing with the inverse (or transpose in this case).

This saves you the trouble of fiddeling with the coordinates inside osg.

> Hello, Robert!
> Thanks for the quick reply.
> It seems i wasn't able to clarify my question. I dont use MatrixTransform or PositionAttitudeTransform here because i don't want to transform my target node relate to others. I want to change local XYZ in that node itself, not the position of my node relate to other nodes or world XYZ.
> Let me describe more specifically.
> Standart aerodynamic convention (and it also looks reasonable in most practical situations) defines local(body) coordinate system as:
> O - center of mass (here just center of a node), X - from center up to nose, Y - from center up to right wing, Z - down. That leads to Roll, Pitch, Yaw rotations around X,Y,Z respectively.
> Let say i want to place camera right behind cessna's tail. Then, AFAIK that code can help me
> Code:
> nodeTracker = new osgGA::NodeTrackerManipulator;
> nodeTracker->setHomePosition( Vec3(-90,0,0), Vec3(), Z_AXIS );
> nodeTracker->setTrackerMode(osgGA::NodeTrackerManipulator::NODE_CENTER_AND_ROTATION );
> nodeTracker->setTrackNode( cessna.get() );
> So: eye Vec3(-90,0,0) means 90 behind center on X. //Local coords, right?
> And of course what we can see now is depended on how X is oriented with respect to model body.
> If, for instance, X has center at model's center and go straight up to nose,
> then -90 means right behind tail (this is what i want to achieve)
> But if X has center at model's center and go from right wing, then -90 means we see left side of an aeroplane, not the tail.
> Then, even when cessna moves correctly (for instance, straight to the north), i see at as moving with right wing forward and nose to the west.
> Also, Roll (rotation about X axis) will be looking like pitch (rotation about Y axis according to aerodynamic standart)
> So to avoid confusion and necessity to remeber how that particular node (cessna) is oriented with respect to its own local coords, maybe the better
> way is to rotate local coords somehow?
> I might be wrong, just to explain why i cannot use Tranform classes according to you advice.
> Could you explain how that problem might be solved?
> Thank you!
> Cheers,
> Elias
> ------------------
> Read this topic online here:
> http://forum.openscenegraph.org/viewtopic.php?p=64161#64161
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