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YTEP-0002: Profile Plotter

Abstract

Created: December 5, 2012 Author: Matthew Turk

This YTEP describes a profile plotting solution, in the style of the PlotWindow, to replace the functionality of the methods on the PlotCollection that create profiles. It should have sane defaults, a restricted set of functionality, and should make accessing the underlying matplotlib axes object very easy.

The method proposed needs to meet several competing needs. It should accept objects, it should "do the right thing" for auto-creating profiles, it should provide access to

Status

In Progress: A basic implementation has been created, but API needs to be decided upon as does the list of functions it will implement.

The code can be seen in yt/visualization/profile_plotter.py, specifically the objects:

  • PhasePlotter
  • ProfilePlotter

Detailed Description

Motivation

The PlotCollection provides an easy way to quickly make profiles and phase plots, both from spheres that it will create and from objects. However, it suffers from a number of deficiencies:

  • Accessing the axes objects from matplotlib is non-trivial
  • Plotting multiple profiles on the same axes object is non-trivial
  • The profile plotter tries to do too many things, and in doing so does not do anything particularly well
  • Profile plots can't be pickled independently of the data

As such, by including this new approach, we will match the functionality from these routines:

  • add_profile_sphere
  • add_profile_object
  • add_phase_sphere
  • add_phase_object

in a way that will enable access to the underlying plots, pickling of plots, and also easier overplotting and multi-plotting.

Implementation

The implementation will need to:

  • Accept a data object and set sane defaults for calculating a profile
  • Not add more than one field to the resulting BinnedProfile object; only one will be added at any time, and additional fields will be left up to the user
  • Include a standalone Plot-type object that contains all of the necessary data to create a representation of the data in Matplotlib.
  • Deposit the plot into an existing Axes or Figure object.
  • Provide simple methods of translating the initial Profile data into the matplotlib object, and allow the user to modify the visualization as she sees fit.

The current implementation contains this class structure:

  • ProfilePlotter * profile: property, the BinnedProfile1D * scale: "log" or "linear", the scale of the profile's y-axis (x-axis is set by the bins in the profile) * _current_field: property, the name of the field currently selected * _setup_plot: Called to create a new plot specification (not a Matplotlib plot) and usually called in the background
  • PhasePlotter * profile: property, the BinnedProfile2D * scale: "log" or "linear", the scale of the profile's y-axis (x-axis and y-axis are set by the bins in the profile) * _current_field: property, the name of the field currently selected * _setup_plot: Called to create a new plot specification (not a Matplotlib plot) and usually called in the background
  • AxisSpec: This specifies the description (title, bounds, scale, ticks) of an Axis. It is typically used without specifying ticks, which are used only by the ExtJS widgets.
  • ColorbarSpec * cmap: property, string * display: property, true or false
  • PlotContainer: Used for profile plots * x_spec: property, AxisSpec * y_spec: property, AxisSpec * x_values: property, numpy array * y_values: property, numpy array * to_mpl: routine that accepts either (Axes), (Figure), or None. Returns the figure and axes after plottin.
  • ImagePlotContainer: Used for phase plots * x_spec: property, AxisSpec * y_spec: property, AxisSpec * image: property, numpy array (2D) * cbar: property, ColorbarSpec instance * to_mpl: routine that accepts either (Axes), (Figure) or None. Returns the figure and axes after plotting.

The indirection enables the user to pickle the plot, without storing the data. But it comes at the price of clarity.

This is currently implemented, and plots returned for the most part to not encourage or allow a substantial amount of modification or fiddling. I think this is okay, as it will very easily allow users to plot multiple lines into the same axes, for instance. However, it does less hand-holding.

Open Questions

  • Should the PhasePlotter and ProfilePlotter objects be refactored to be explicitly favoring matplotlib? The PlotWindow does this, and it is successful.
  • Should we allow users to dynamically switch fields on the fly?
  • Should the desire for pickling of objects be given up in favor of a cleaner and simpler class structure? (i.e., getting rid of the Specification objects.)

Backwards Compatibility

We will not remove the existing functionality from PlotCollection. So there are no backwards compatibility issues.

Alternatives

Alternately, we could provide nothing, and encourage users to create their own BinnedProfile1D plots. Or, we could provide a much more specific-to-MPL alternative.