Re: [Matplotlib-users] Some more mplot3d questions

Hi Ben,
Comments inline...

On Fri, Jul 22, 2011 at 1:31 AM, Benjamin Root <ben...@ou...> wrote:
>
>
> On Thu, Jul 21, 2011 at 1:10 AM, gary ruben <gar...@gm...> wrote:
>>
>> I'm trying to make a surface plot using the latest version of mplot3d
>> from the git trunk and I have a couple of questions. The attached
>> image is close to what I would like. The associated plot command I am
>> using is
>>
>> ax.plot_surface(X, Y, Z, rstride=1, cstride=1, alpha=0.8, shade=True,
>>    cmap=plt.cm.summer,
>>    color='k',
>>    facecolors='k',
>>    lightsource = LightSource(azdeg=0, altdeg=0),
>>    )
>>
>> 1. Is there support now to automatically annotate the axis so that a
>> multiplier is added, as occurs in 2D plots, or should I do this
>> manually by rescaling the data for the moment?
>
> Yes, offset text is now automatic and should activate in similar manner as
> it does for regular 2D axis formatters.  You were one order of magnitude off
> from automatically triggering it.  Also, I should note that it might be
> better to use "ax = fig.gca(projection='3d')" instead of "ax = Axes3D(fig)"
> because the former will leave more of a margin, which would allow the offset
> text to be fully visible.

Thanks. That's actually what I am doing but I cropped the output image
before attaching it.

> If you want the full figure area, then you may
> need to fiddle with the ax.zaxis._axinfo['label']['space_factor'] to bring
> it and the axis label closer to the axis.

Thanks. That's useful to know.

> The odd thing that I am encountering right now while investigating your
> problem is that I can't seem to force the use of the offset.  It could just
> be that I am doing it wrong, but I will look closer.

Yes, I had set 'axes.formatter.limits' : (-2, 2) hoping to trigger it
- I guess that's what you tried.

>> 2. Currently, it doesn't appear possible to shade the surface patches
>> according to just a base facecolor and their orientation to a light
>> source. Do I have to define a new colormap with a constant/single
>> colour to achieve this?
>
> Looking over the plot_surface code, this appears to be the case, however,
> looking back over the LightSource code, I believe it might be possible to
> update plot_surface to operate on situations where no cmap is specified.  I
> will take a look today at that possibility and see if I can get it out for
> the v1.1.0 release.

That would be great - it is a very good way to visualize a surface so
it should be made as simple as possible.

>> 3. I have set alpha=0.8 to allow the wireframe lines to show through a
>> little. When shade=False, the wireframe is visible but I lose
>> orientation-based shading. Is there a way to overlay the wireframe
>> properly when shade=True?
>>
>
> In plot_surface, when shade=True, it appears that both the facecolors and
> the edgecolors are set to the same colors.  The only reason why the lines
> show up when you set transparency is that that alpha value is applied only
> to the faces and not the edges.  Specifically, the logic is as follows:
>
> if fcolors is specified, then set that color for both facecolor and
> edgecolor.
> Else, if a cmap is specified, then give the polygon collection the data,
> limits and norm it needs to determine color itself.
> Else, then use the value of "color" to specify only the facecolors.
>
> I think the first branch of this logic is a bit wonky.

I agree, since fcolors must be specified in order to trigger the
lightsource-based shading.

> I am inclined to
> make a small change that would only set the edgecolors if 'edgecolors' was
> not provided as a kwarg.  This would enable users to specify the edgecolor
> they want without worrying about something else over-riding it.  The only
> problem seems to be that there would be no shading of these grid lines.
> Would that still be acceptable to you?

Absolutely acceptable. In fact I think it is preferable not to shade them.

> Thanks for your valuable feedback!
> Ben Root

Thanks for being responsive to it :)
regards,
Gary