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  #1  
Old 10-13-2009, 12:27 PM
whj whj is offline
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Join Date: Apr 2008
Posts: 60
positions on animation path

Hi, I would like to create an environment in which a ball is going around the original point. My simple code just create an animation path of a circle for a ball and try to figure out the actual positions when the ball pass along the animation path. My question is why the printed positions are not on a circle like what we can see? And so why the distance between the ball and the original point are not the constant value 10? Thanks!


Code:
import viz
viz.go()

import math

viz.add('tut_ground.wrl')
ball = viz.add('ball.wrl')

viz.MainView.move([0,3,-20])

path = viz.addAnimationPath()
positions = [ [0,1,10], [10,1,0], [0,1,-10], [-10,1,0], [0,1,10] ]
for x in range(len(positions)):
	cp = viz.add(viz.CONTROL_POINT)
	cp.setPosition(positions[x])
	path.add(cp,x+1)

path.loop(viz.CIRCULAR)
viz.CUBIC_BEZIER
path.translatemode(viz.BEZIER)
path.computetangents()
path.setAutoRotate(viz.ON)

mylink = viz.link(path,ball)
path.play()

def mytimer(num):
	pc = ball.getPosition()
	print 'position: ', pc

	dist = math.sqrt( (pc[0]-0.0)*(pc[0]-0.0) + (pc[2]-0.0)*(pc[2]-0.0) )
	print 'distance: ', dist

	
viz.callback(viz.TIMER_EVENT, mytimer)
viz.starttimer(0,1/60.0,viz.FOREVER)
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  #2  
Old 10-16-2009, 12:19 PM
farshizzo farshizzo is offline
WorldViz Team Member
 
Join Date: Mar 2003
Posts: 2,849
You won't be able to create a perfect circle using bezier paths. You are better off manually animating the object. Either way, the following modified version of your script will generate a path that is closer to a circle. It uses cubic bezier and you removes the duplicate control point at the end of the path:
Code:
import viz
import vizmat
import vizact
viz.go()

viz.add('tut_ground.wrl')
ball = viz.add('ball.wrl')

viz.MainView.move([0,3,-20])

path = viz.addAnimationPath()
positions = [ [0,1,10], [10,1,0], [0,1,-10], [-10,1,0] ]
for x,pos in enumerate(positions):
	cp = viz.addControlPoint()
	cp.setPosition(pos)
	path.add(cp,x+1)

path.loop(viz.CIRCULAR)
path.translatemode(viz.CUBIC_BEZIER)
path.computetangents()
path.setAutoRotate(viz.ON)

mylink = viz.link(path,ball)
path.play()

def PrintInfo():
	pc = ball.getPosition()
	print 'position: ', pc

	dist = vizmat.Distance(pc,[0,1,0])
	print 'distance: ', dist

vizact.ontimer(0,PrintInfo)
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  #3  
Old 10-19-2009, 03:13 PM
whj whj is offline
Member
 
Join Date: Apr 2008
Posts: 60
I'll try that. Thank you.
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  #4  
Old 10-27-2009, 01:21 PM
whj whj is offline
Member
 
Join Date: Apr 2008
Posts: 60
Hi,

If I happen to create another non-circle path using bezier paths, would the distance we can see/feel in VR is close to the actual distance that calculated by vizmat.Distance().

Thanks!



Quote:
Originally Posted by farshizzo View Post
You won't be able to create a perfect circle using bezier paths. You are better off manually animating the object. Either way, the following modified version of your script will generate a path that is closer to a circle. It uses cubic bezier and you removes the duplicate control point at the end of the path:
Code:
import viz
import vizmat
import vizact
viz.go()

viz.add('tut_ground.wrl')
ball = viz.add('ball.wrl')

viz.MainView.move([0,3,-20])

path = viz.addAnimationPath()
positions = [ [0,1,10], [10,1,0], [0,1,-10], [-10,1,0] ]
for x,pos in enumerate(positions):
	cp = viz.addControlPoint()
	cp.setPosition(pos)
	path.add(cp,x+1)

path.loop(viz.CIRCULAR)
path.translatemode(viz.CUBIC_BEZIER)
path.computetangents()
path.setAutoRotate(viz.ON)

mylink = viz.link(path,ball)
path.play()

def PrintInfo():
	pc = ball.getPosition()
	print 'position: ', pc

	dist = vizmat.Distance(pc,[0,1,0])
	print 'distance: ', dist

vizact.ontimer(0,PrintInfo)
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