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On 2/24/2013 1:28 PM, Paul Anton Letnes wrote:
> Hi everyone,
>
> I've been looking into making an animation of a mechanical system. In its first incarnation, my plan was as follows:
> 1) Make a fading line plot of two variables (say, x and y)
> 2) Run a series of such plots through ffmpeg/avencode to generate an animation
>
> First, I'm wondering whether there's a built-in way of making a fading line plot, i.e. a plot where one end of the line is plotted with high alpha, the other end with low alpha, and intermediate line segments with linearly scaled alpha. For now, I've done this by manually "chunking" the x and y arrays and plotting each chunk with different alpha. Is there a better way? Is there interest in creating such a plotting function and adding it to matplotlib?
>
> Second, is there a way of integrating the "chunked" generation of fading lines with the animation generating features of matplotlib? It seems possible, although a bit clunky, at present, but maybe someone has a better idea at what overall approach to take than I do.
>
> Cheers
> Paul
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Paul,
I've had to do something similar to what you need, and I found the 
following example from the Gallery quite helpful:
http://matplotlib.org/examples/pylab_examples/multicolored_line.html
I think the second plot in particular is pretty close to what you want; 
however, you'll need to set the alpha values manually. This is what I've 
done for line collections, scatter plots, etc.
_________________________________
import numpy as np
import matplotlib.pyplot as plt
norm_data = np.random.rand(20)
xs = np.random.rand(20)
# Pick a colormap and generate the color array for your data
cmap = plt.cm.spectral
colors = cmap(norm_data)
# Reset the alpha data using your desired values
colors[:,3] = norm_data
# Adding a colorbar is a bit of a pain here, need to use a mappable
fig = plt.figure()
plt.scatter(xs, norm_data, c=colors, s=55)
mappable = plt.cm.ScalarMappable(cmap=cmap)
mappable.set_array(norm_data)
fig.colorbar(mappable)
plt.show()
_________________________________
Hope that helps a little.
Ryan

On 24/02/2013 18:28, Paul Anton Letnes wrote:
> Hi everyone,
>
> I've been looking into making an animation of a mechanical system. In its first incarnation, my plan was as follows:
> 1) Make a fading line plot of two variables (say, x and y)
> 2) Run a series of such plots through ffmpeg/avencode to generate an animation
>
> First, I'm wondering whether there's a built-in way of making a fading line plot, i.e. a plot where one end of the line is plotted with high alpha, the other end with low alpha, and intermediate line segments with linearly scaled alpha. For now, I've done this by manually "chunking" the x and y arrays and plotting each chunk with different alpha. Is there a better way? Is there interest in creating such a plotting function and adding it to matplotlib?
>
> Second, is there a way of integrating the "chunked" generation of fading lines with the animation generating features of matplotlib? It seems possible, although a bit clunky, at present, but maybe someone has a better idea at what overall approach to take than I do.
>
> Cheers
> Paul
> ------------------------------------------------------------------------------
> Everyone hates slow websites. So do we.
> Make your web apps faster with AppDynamics
> Download AppDynamics Lite for free today:
> http://p.sf.net/sfu/appdyn_d2d_feb
>
I remember this 
http://www.johndcook.com/blog/2013/02/20/python-animation-for-mechanical-vibrations/ 
from a few days back, HTH.
-- 
Cheers.
Mark Lawrence

Hi everyone,
I've been looking into making an animation of a mechanical system. In its first incarnation, my plan was as follows:
1) Make a fading line plot of two variables (say, x and y)
2) Run a series of such plots through ffmpeg/avencode to generate an animation
First, I'm wondering whether there's a built-in way of making a fading line plot, i.e. a plot where one end of the line is plotted with high alpha, the other end with low alpha, and intermediate line segments with linearly scaled alpha. For now, I've done this by manually "chunking" the x and y arrays and plotting each chunk with different alpha. Is there a better way? Is there interest in creating such a plotting function and adding it to matplotlib?
Second, is there a way of integrating the "chunked" generation of fading lines with the animation generating features of matplotlib? It seems possible, although a bit clunky, at present, but maybe someone has a better idea at what overall approach to take than I do.
Cheers
Paul