Accessing position list

[Josh Gates]

Is there a method to access the stored set of positions in a curve (trail)?

I'm trying to plot via matplotlib, and instead of creating my own variable to accumulate the points, I'd like to access the stored set of points in the trail, if possible. Is there anything else odd about that workflow that I'm not considering? I know that, when there's a long trail, it seems like it doesn't display all of the points in the curve - I assume that's just a display change (modifying the interval), but I'm not positive.

Thanks,

jg

[Bruce Sherwood]

No, there's isn't currently a way to access the points in a trail. I'm not aware of a long trail not showing all points; do you have an example? There was something like this in Classic VPython, but not in GlowScript or Jupyter VPython.

For your purposes it makes sense not to use the trail machinery but to append points to your own curve object (and to a list), so that you have complete control. Be aware that typically you shouldn't add a point every time you update the position of an object, because that could mean you would be adding several hundred points per second, and a curve with a very large number of points displays slowly.

[Josh Gates]

I was assuming that GS had the same behavior as classic VP - thanks for clarifying that. 

What's the method for accessing the points list of a curve object?

Thanks,

jg

On Thu, Aug 4, 2016 at 3:37 PM, Bruce Sherwood <bruce.s...@gmail.com> wrote:

No, there's isn't currently a way to access the points in a trail. I'm not aware of a long trail not showing all points; do you have an example? There was something like this in Classic VPython, but not in GlowScript or Jupyter VPython.

For your purposes it makes sense not to use the trail machinery but to append points to your own curve object (and to a list), so that you have complete control. Be aware that typically you shouldn't add a point every time you update the position of an object, because that could mean you would be adding several hundred points per second, and a curve with a very large number of points displays slowly.

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Joshua Gates

[Bruce Sherwood]

See the GlowScript help article on the curve object.

But in your case, if you append your own points to a curve object you could easily append the same point to your own list. There's no need to read from the curve later.

[Bruce Sherwood]

Another scheme is to use make_trail and periodically, when you update pos, append pos to a list of positions. Something like this:

count = 10

while True:

    newpos = .....

    ball.pos = newpos

    if count == 0:

        poslist.append(newpos)

        count = 0

    else:

        count -= 1

[Josh Gates]

That's pretty similar to what I was doing (except that I was keeping the count going and using modular arithmetic to get every 200th point) - works fine!

Thanks,

jg