Using a custom frame¶
By default, WCSAxes
will make use of a rectangular
frame for a plot, but this can be changed to provide any custom frame. The
following example shows how to use the built-in
EllipticalFrame
class, which is an ellipse which extends to the same limits as the built-in rectangular frame:
from astropy.wcs import WCS
from wcsaxes import datasets
from wcsaxes.frame import EllipticalFrame
hdu = datasets.fetch_msx_hdu()
wcs = WCS(hdu.header)
import matplotlib.pyplot as plt
fig = plt.figure()
ax = fig.add_axes([0.15, 0.15, 0.7, 0.7], projection=wcs,
frame_class=EllipticalFrame)
ax.coords.grid(color='white')
im = ax.imshow(hdu.data, vmin=-2.e-5, vmax=2.e-4, cmap=plt.cm.gist_heat,
origin='lower')
# Clip the image to the frame
im.set_clip_path(ax.coords.frame.patch)
However, you can also write your own frame class. The idea is to set up any number of connecting spines that define the frame. You can define a frame as a spine, but if you define it as multiple spines you will be able to control on which spine the tick labels and ticks should appear.
The following example shows how you could for example define a hexagonal frame:
from wcsaxes.frame import BaseFrame
class HexagonalFrame(BaseFrame):
spine_names = 'abcdef'
def update_spines(self):
xmin, xmax = self.parent_axes.get_xlim()
ymin, ymax = self.parent_axes.get_ylim()
ymid = 0.5 * (ymin + ymax)
xmid1 = (xmin + xmax) / 4.
xmid2 = (xmin + xmax) * 3. / 4.
self['a'].data = np.array(([xmid1, ymin], [xmid2, ymin]))
self['b'].data = np.array(([xmid2, ymin], [xmax, ymid]))
self['c'].data = np.array(([xmax, ymid], [xmid2, ymax]))
self['d'].data = np.array(([xmid2, ymax], [xmid1, ymax]))
self['e'].data = np.array(([xmid1, ymax], [xmin, ymid]))
self['f'].data = np.array(([xmin, ymid], [xmid1, ymin]))
which we can then use:
from astropy.wcs import WCS
from wcsaxes import datasets
hdu = datasets.fetch_msx_hdu()
wcs = WCS(hdu.header)
import matplotlib.pyplot as plt
fig = plt.figure()
ax = fig.add_axes([0.15, 0.15, 0.7, 0.7], projection=wcs,
frame_class=HexagonalFrame)
ax.coords.grid(color='white')
im = ax.imshow(hdu.data, vmin=-2.e-5, vmax=2.e-4, cmap=plt.cm.gist_heat,
origin='lower')
# Clip the image to the frame
im.set_clip_path(ax.coords.frame.patch)
Frame properties¶
The color and linewidth of the frame can also be set by
ax.coords.frame.set_color('red')
ax.coords.frame.set_linewidth(2)