colormap support for 3d quiver

[twmr]

It would be nice to have support for a colormap kwarg (like the C kwarg in the 2d implementation of quiver http://matplotlib.org/api/axes_api.html?highlight=quiver#matplotlib.axes.Axes.quiver) in the 3d version of quiver.

[tacaswell]

cc @WeatherGod

[perimosocordiae]

It's currently possible to do this with a little bit of colormap trickery. Assuming you have an array of scalar color values between 0 and 1 named C:

cmap = plt.get_cmap()
ax.quiver(x,y,z,u,v,w,color=cmap(C))

I agree that support for this would be nice to have directly in the quiver function itself.

[tacaswell]

This actually goes back to a limitation of the LineCollection class...

[perimosocordiae]

I also just realized that you'd need to do np.repeat(C, 3) first, because quiver creates three lines for each arrow in the plot.

[delooper]

I'm reading in the linecollection API for matplotlib 1.5.1 and it looks like you should be able to assign colors arrow-by-arrow but I haven't determined what format the library wants the call to be in. The library makes it sound like it needs a nxmxkx3 or a nxmxkx4 array depending on if you are using RGB or RGBA colors. But I'm not having any luck with it.

[WeatherGod]

Most likely, the problem is that the colors might be getting re-assigned by
other parts of mplot3d. Color-handling has been extremely tricky in mplot3d.

On Thu, Mar 17, 2016 at 5:02 PM, Ryan Budney notifications@github.com
wrote:

I'm reading in the linecollection API for matplotlib 1.5.1 and it looks
like you should be able to assign colors arrow-by-arrow but I haven't
determined what format the library wants the call to be in. The library
makes it sound like it needs a nxmxkx3 or a nxmxkx4 array depending on if
you are using RGB or RGBA colors. But I'm not having any luck with it.

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#3382 (comment)

[delooper]

Do you know if one can change the length or width of a 3d quiver plot, element-by-element? I haven't had luck with that, either.

[sytrus-in-github]

@delooper I have just opend another issue on specifying colors for each arrow in 3D quiver plot (since this one is more about colormap) in which I have given a work around for my case:

• reshape your array of shape (n,m,k,3) to (n*m*k, 3) (4 for RGBA I suppose)
• filter out color values corresponding to vectors of length 0 because they won't be drawn ...
• specify colors = array + repeatEachElement(array, 2) since first all "-" part of "->" will be drawn then the ">" part will be drawn

Hope this helps.

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