[Matplotlib-users] axes properties

Tue Mar 21 10:21:44 EDT 2017

Jean-Philippe,

To answer your second question, you can use the `view_init()` method of the
axes to change the orientation of the axes:
http://matplotlib.org/mpl_toolkits/mplot3d/api.html#mpl_toolkits.mplot3d.axes3d.Axes3D.view_init

An example using it to do a "rotation":
http://matplotlib.org/examples/mplot3d/rotate_axes3d_demo.html

I hope that helps!
Ben Root

On Tue, Mar 21, 2017 at 9:57 AM, vincent.adrien at gmail.com <
vincent.adrien at gmail.com> wrote:

> Dear Jean-Philippe,
>
> (If I correctly understood your question 1.:) `fig.add_subplot` creates an
> Axes
> instance where you can then plot more or less *any* kind of plot that
> Matplotlib
> supports (line, scatter, hist, patch, etc.). *It is not specific to the
> '3d'
> projection.* `fig.add_subplot(1, 1, 1)` (or `fig.add_subplot(111)` if your
> prefer a syntax closer to MATLAB) simply means that you want to create a
> single
> (sub)plot area on your figure canvas. If you are confused because in 2D you
> could get a line plot simply with `plt.plot([0, 1, 2])`, understand that
> under
> the hood it is only some kind of wrapper for the (OO-)equivalent:
> ```python
> fig = plt.figure()
> ax = fig.add_subplot(1, 1, 1)
> ax.plot([0, 1, 2])
> ```
> The difference here to get a 3D Axes instance is that you have to precise
> the
> projection when you create it (`fig.add_subplot(1, 1, 1,
> projection='3d')`).
>
> Besides (if I am correct), please note that “we” tend to promote using an
> equivalent (but more OO-)wrapper, namely `plt.subplots` (the final *s* is
> important!). In 2D, you can thus write
> ```python
> fig, ax = plt.subplots()  # create a "111-subplot"
> ax.plot([0, 1, 2])
> ```
> and you can pass different **kwargs to it, among which a 'subplot_kw'
> dictionary
> that allows you to precise the projection. For example if you want to get a
> "111-subplot" 3d Axes:
> ```
> fig, ax = plt.subplots(subplot_kw={'projection': '3d'})
> ```
> It is a bit verbose is this simple situation but becomes rather convenient
> for
> grids with several subplots.
>
> About 2. you may want to have a look at the following properties and
> methods:
> - ax.dist
> - ax.azim
> - ax.elev
> - ax.view_init(elev=..., azim=...)
>
> Here is a small script (PNG output is attached) that demonstrate their
> usage:
> ```python
> import numpy as np
> import matplotlib.pyplot as plt
> from mpl_toolkits.mplot3d import Axes3D
>
>
> def dummy_plot(ax):
>     X, Y = np.meshgrid(np.arange(-5, 5, 0.25), np.arange(-5, 5, 0.25))
>     Z = np.sin(np.sqrt(X**2 + Y**2))
>     ax.plot_surface(X, Y, Z, cmap='coolwarm')
>     # Remove all the ticks for eye pleasure
>     ax.xaxis.set_major_locator(plt.NullLocator())
>     ax.yaxis.set_major_locator(plt.NullLocator())
>     ax.zaxis.set_major_locator(plt.NullLocator())
>     return ax
>
> # Here is a way to instantiate all the 2x2 subplots at once, without using
> # the `fig.add_subplot` method. *axs* is a 2x2-array of Axes instances.
> fig, axs = plt.subplots(nrows=2, ncols=2, figsize=(6.4, 4.8),
>                         num="Demo_Jean-Philippe_GRIVET_2",  # <- figure
> label
>                         subplot_kw={'projection': '3d'})
>
> ax = dummy_plot(axs[0, 0])
> ax.set_title("Forced defaults: dist=10 (a.u.),\nazim=-60 (deg), elev=30
> (deg)")
> # NB: these values does not seem to be exactly the (1, 1, 1) direction to
> me.
> ax.dist = 10
> ax.view_init(azim=-60, elev=30)
> # From the docstring of `ax.view_init`:
> # Set the elevation and azimuth of the axes. This can be used to rotate
> # the axes programatically:
> # - 'elev' stores the elevation angle in the z plane.
> # - 'azim' stores the azimuth angle in the x,y plane.
>
> ax = dummy_plot(axs[0, 1])
> ax.set_title("Doubled 'dist' value")
> ax.dist *= 2
>
> # NB: one can also directly set the `ax.azim` and `ax.elev` properties
> ax = dummy_plot(axs[1, 0])
> ax.set_title("'azim' increased of 45 deg.")
> ax.azim += 45
>
> ax = dummy_plot(axs[1, 1])
> ax.set_title("'elev' set to 60 deg.")
> ax.elev = 60
>
> plt.tight_layout()
> plt.show()
> ```
>
> Hopefully it will help you to plot what you want :).
>
> Best,
> Adrien
>
> On 18/03/2017 17:56, Jean-Philippe GRIVET wrote:
> > Thank you so much Vincent  (and Amit) for your detailed answers.
> >
> > I have two questions remaining.
> >
> > 1. All the code examples that I have looked at (including the "getting
> > started" example on page 1798 of the user manual for Matplotlib 2.0)
> > uses the "add_subplot" metod. Why should a 3d projection be included
> > in a subplot and not in a plot ?
> >
> > 2. In all the examples, the figure seems to be viewed down the 1,1,1
> > direction towards the origin. How can the view point be changed from
> > within the program ?
> >
> > Thanks again,
> > Jean-Philippe
>
>
>
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