speed on animation path
 

Hello Jeff,

Previously you helped me out with the problem that how to get the position of an object two seconds ahead. Thanks a lot. Here is the code with slight change on your code, in which a semi-transparent ball two seconds ahead of another ball on animation path. I have a question about their speed. Why the speed of balls changes a lot along the animation path although I used path.constantspeed(viz.ON,4). How can I get a smooth constant speed? Thanks.


import viz
viz.go()

viz.add('tut_ground.wrl')

ball = viz.add('ball.wrl')
ball.alpha(.5)
ball2 = viz.add('ball.wrl')

viz.MainView.move(0,3,-30)

path = viz.add(viz.ANIMATION_PATH)
path2 = viz.add(viz.ANIMATION_PATH)

positions = [ [2,0.15,50], [1,0.15,35], [0,0.15,25], [-4,0.15,15], [-10,0.15,8], [-25,0.15,0], [-15,0.15,-8], [-10,0.15,-10], [-6,0.15,-12], [-3,0.15,-15], [0,0.15,-18], [3,0.15,-16], [6,0.15,-8], [10,0.15,2], [15,0.15,0], [25,0.15,-12], [35,0.15,-12], [50,0.15,-12], [70,0.15,10], [90,0.15,30], [140,0.15,120] ]

for x in range(0,len(positions)):
cp = viz.add(viz.CONTROL_POINT)
cp.setPosition(positions[x])
path.add(cp,x+1)
path2.add(cp,x+1)


path.constantspeed(viz.ON,4)
path2.constantspeed(viz.ON,4)


path.loop(viz.OFF)
path2.loop(viz.OFF)

path.translatemode(viz.BEZIER)
path2.translatemode(viz.BEZIER)

path.setAutoRotate(viz.ON)
path2.setAutoRotate(viz.ON)

#Link ball and ball2 to their paths
ball.link(path)
ball2.link(path2)


#start playing the first animation path immediately
path.play()

#start playing the second animation path after two seconds
vizact.ontimer2(2, 1, path2.play)

thanks for the post, we'll get back to you as soon as we can on this

the constantspeed method does not work with the bezier translation mode. If you use it with one of the other modes it should be fine.

Seems that computeTangents() mode doesn't work too. Then how can I smoothly move a object in a specified curve with constent speed?

Thanks,

Are you using

I think this should work with constantspeed. Can you post an example with how you are using it.

Thanks Jeff. I didn't put path.translatemode(viz.CUBIC_BEZIER) in my code.:p Yes, cubic_bezier mode has constant speed.

BTW, it's not bad for me to specify all positions of a animation path using bezier translation mode, but it is really hard to find positions in cubic_bezier translation mode. Having a cubic-bezier curve, do you have any easy way to get its intermediate points?

Thanks,
whj

Hi Jeff,

Please see the following code. The car speed up when it turns. Seems still not constant speed for some curves. How can I improve it? About cubic_bezier curve, do I specify only 4 points for a curve? If the curve is complex, could I include more points?

import viz
viz.go()

viz.add('tut_ground.wrl')

ball = viz.add('ball.wrl')
ball.alpha(.5)
car = viz.add('mini.osgx')

viz.MainView.move(0,3,-60)

path = viz.add(viz.ANIMATION_PATH)
path2 = viz.add(viz.ANIMATION_PATH)

positions = [ [7,0.15,-50], [5,0.15,10], [20,0.15,-10], [140,0.15,120] ]
for x in range(0,len(positions)):
cp = viz.add(viz.CONTROL_POINT)
cp.setPosition(positions[x])
path.add(cp,x+1)
path2.add(cp,x+1)


path.constantspeed(viz.ON,4)
path2.constantspeed(viz.ON,4)


path.loop(viz.OFF)
path2.loop(viz.OFF)

path.translatemode(viz.CUBIC_BEZIER)
path.computetangents()
path2.translatemode(viz.CUBIC_BEZIER)
path2.computetangents()

path.setAutoRotate(viz.ON)
path2.setAutoRotate(viz.ON)

#Link ball and ball2 to their paths
ball.link(path)
car.link(path2)


#start playing the first animation path immediately
path.play()

#start playing the second animation path after two seconds
vizact.ontimer2(2, 1, path2.play)

Yes, your right. I guess the constantspeed does not work with Cubic Bezier either. Would defining more points on the curve and using the linear mode work for your situation

OK. Thanks for your help.