Spherical ProjectionsΒΆ
Figure 1.14.
Four common full-sky projections. The shaded ellipses represent the distortion across the sky: each is projected from a circle of radius 10 degrees on the sphere. The extent to which these are distorted and/or magnified shows the distortion inherent to the mapping.
# Author: Jake VanderPlas
# License: BSD
# The figure produced by this code is published in the textbook
# "Statistics, Data Mining, and Machine Learning in Astronomy" (2013)
# For more information, see http://astroML.github.com
# To report a bug or issue, use the following forum:
# https://groups.google.com/forum/#!forum/astroml-general
import numpy as np
from matplotlib import pyplot as plt
from astroML.plotting import plot_tissot_ellipse
#----------------------------------------------------------------------
# This function adjusts matplotlib settings for a uniform feel in the textbook.
# Note that with usetex=True, fonts are rendered with LaTeX. This may
# result in an error if LaTeX is not installed on your system. In that case,
# you can set usetex to False.
from astroML.plotting import setup_text_plots
setup_text_plots(fontsize=8, usetex=True)
#------------------------------------------------------------
# generate a latitude/longitude grid
circ_long = np.linspace(-np.pi, np.pi, 13)[1:-1]
circ_lat = np.linspace(-np.pi / 2, np.pi / 2, 7)[1:-1]
radius = 10 * np.pi / 180.
#------------------------------------------------------------
# Plot the built-in projections
plt.figure(figsize=(5, 4))
plt.subplots_adjust(hspace=0, wspace=0.12,
left=0.08, right=0.95,
bottom=0.05, top=1.0)
for (i, projection) in enumerate(['Hammer', 'Aitoff', 'Mollweide', 'Lambert']):
ax = plt.subplot(221 + i, projection=projection.lower())
ax.xaxis.set_major_locator(plt.FixedLocator(np.pi / 3
* np.linspace(-2, 2, 5)))
ax.xaxis.set_minor_locator(plt.FixedLocator(np.pi / 6
* np.linspace(-5, 5, 11)))
ax.yaxis.set_major_locator(plt.FixedLocator(np.pi / 6
* np.linspace(-2, 2, 5)))
ax.yaxis.set_minor_locator(plt.FixedLocator(np.pi / 12
* np.linspace(-5, 5, 11)))
ax.grid(True, which='minor')
plot_tissot_ellipse(circ_long[:, None], circ_lat, radius,
ax=ax, fc='k', alpha=0.3, linewidth=0)
ax.set_title('%s projection' % projection)
plt.show()