WorldViz User Forum - positions on animation path

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- - positions on animation path (https://forum.worldviz.com/showthread.php?t=2320)

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)

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)

I'll try that. Thank you.

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 (Post 8852)

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)