Re: [Matplotlib-users] The shape of symbols in some scatter plots.

[John H. <jdh...@ac...>]

>>>>> "Paul" == Paul Barrett <ba...@st...> writes:

    Paul> I occasionally use the scatter() function to make light
    Paul> curves of astronomical targets.  The scale of the x-axis is
    Paul> often given in days with a range of 0.54 - 0.68 days.  The
    Paul> y-axis is in counts.  This type of data produces unusual
    Paul> scatter plots with the blue symbols being very elongated
    Paul> ovals (in the x-direction).

    Paul> Are there plans to change this behavior - maybe by drawing
    Paul> the symbols in device space instead of data or user space?

There are a couple of ways to do this.

The line style provides markers, the sizes of which are in points.  If
you want fixed size markers independent of data coords, you can use
plot with the 'o' marker symbol (or any other marker symbol), and then
set the marker size, facecolor, and edgecolor, as you desire

  markers = plot(x, y, 'o')
  set(markers, 'markersize', 20)
  set(markers, 'markeredgecolor', 'k')
  set(markers, 'markerfacecolor', 'b')

The set function takes a sequence of markers and applies the arguments
to all of them.  To control the marker properties separately, you can
do (for example)

  rgbs = [ ... ]   # a len x list of rgb tuples
  sizes = [ ... ]  # a len x list of marker sizes in points
  for m, rgb, size in zip(markers, rgbs, sizes):
      m.set_markerfacecolor(rgb)
      m.set_markersize(size)
   
See the documentation for matplotlib.lines for more info.

Patches (which is what scatter and hist create) on the other hand, are
in data coordinates by default.  This too can be changed by setting
the transformation functions.  You can, for example, specify the
patches in relative (0, 1) axes coords with a little extra work.  All
the figure "Artists" can be placed with arbitrary transforms -- see
matplotlib.transforms for more info.  Many of these features could use
some better documentation....

My guess is that you will be happy with the line markers -- let me
know.

JDH