Quaternions

[roman_suvorov]

All right, I've read QUITE A BIT about quaternions at this point but still don't get them ..

Here's some sample code. Copy/paste and run this:

import viz
viz.go(viz.FULLSCREEN)

ROTATION_INC = 2
TRANSLATE_INC = 0.1

i = 0
while (i < 50):
	redBall = viz.add("white_ball.wrl")
	redBall.setPosition([i, 0, 0])
	redBall.color([255, 0, 0])
	
	greenBall = viz.add("white_ball.wrl")
	greenBall.setPosition([0, i, 0])
	greenBall.color([0, 255, 0])
	
	blueBall = viz.add("white_ball.wrl")
	blueBall.setPosition([0, 0, i])
	blueBall.color([0, 0, 255])
	
	i += 0.1
	
viz.MainView.setQuat([0,1,0,0])
viz.MainView.setPosition(5, 0, 0.5)
	
vizact.whilekeydown(viz.KEY_UP, viz.move, 0, 0, TRANSLATE_INC)
vizact.whilekeydown(viz.KEY_DOWN, viz.move, 0, 0, -TRANSLATE_INC)
vizact.whilekeydown(viz.KEY_LEFT, viz.rotate, viz.BODY_ORI, -ROTATION_INC, 0, 0)
vizact.whilekeydown(viz.KEY_RIGHT, viz.rotate, viz.BODY_ORI, ROTATION_INC, 0, 0)
vizact.whilekeydown(viz.KEY_PAGE_UP, viz.rotate, viz.HEAD_ORI, 0, -ROTATION_INC, 0)
vizact.whilekeydown(viz.KEY_PAGE_DOWN, viz.rotate, viz.HEAD_ORI, 0, ROTATION_INC, 0)

You will see a red "line" in front of you. Look around using left/right arrow keys, tilt your "head" up/down using PgUp/PgDown keys, move forward/backward using up/down arrow keys.
What this is meant to be is "training grounds" for understanding quaternions. If you look at the code inside the while loop you'll see that X-axis is traced with red dots, Y with green, Z with blue (X-Y-Z -> R-G-B was my logic ).
MainView's originally just slightly off red Y-axis and the rotation is set to [x,y,z,w] = [0,1,0,0].
What I'm trying to understand now that we have a well-defined system of coordinates right in front of us is how quaternions work: [0,1,0,0] SHOULD have defined a rotation of 0 degrees around axis [0,1,0] - the Y-axis, so the camera originally should just look down the green Y-axis. Instead we're looking down X!
I hope someone more experienced with quaternions can explain to me how they work in Vizard using this simple script, that would be great. Thanks!

[farshizzo]

In my previous post I explained what the values mean. So given the quaternion rotation of [0,1,0,0], this would mean a 180 degree rotation around the Y axis (2 * acos(0) = 180 degrees). Printing the euler and axis-angle values of the main view after applying the quaternion will confirm this. Adding the following code at the end of the script:

print viz.MainView.getEuler()
print viz.MainView.getAxisAngle()

resulted in the following output:

[-180.0, 0.0, 0.0]
[0.0, -1.0, 0.0, 180.0]

FYI, Vizard color values range from 0-1, not 0-255.