Introduction
In this lab, we will learn how to use GridHelperCurveLinear to create custom grid and tick lines in Matplotlib. We will also learn how to create a polar projection in a rectangular box.
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Grid for Custom Transform
First, we will create a custom grid and tick lines using GridHelperCurveLinear. The custom transform will be applied to the grid and tick lines. The following code demonstrates this process:
import matplotlib.pyplot as plt
import numpy as np
from matplotlib.projections import PolarAxes
from matplotlib.transforms import Affine2D
from mpl_toolkits.axisartist import Axes, HostAxes, angle_helper
from mpl_toolkits.axisartist.grid_helper_curvelinear import GridHelperCurveLinear
def curvelinear_test1(fig):
# Define custom transform
def tr(x, y):
return x, y - x
def inv_tr(x, y):
return x, y + x
# Create GridHelperCurveLinear object
grid_helper = GridHelperCurveLinear((tr, inv_tr))
# Create a subplot with the custom grid and tick lines
ax1 = fig.add_subplot(1, 2, 1, axes_class=Axes, grid_helper=grid_helper)
# Plot some points on the subplot
xx, yy = tr(np.array([3, 6]), np.array([5, 10]))
ax1.plot(xx, yy)
# Set the aspect ratio and limits of the subplot
ax1.set_aspect(1)
ax1.set_xlim(0, 10)
ax1.set_ylim(0, 10)
# Add floating axes and grid lines
ax1.axis["t"] = ax1.new_floating_axis(0, 3)
ax1.axis["t2"] = ax1.new_floating_axis(1, 7)
ax1.grid(True, zorder=0)
fig = plt.figure(figsize=(7, 4))
curvelinear_test1(fig)
plt.show()
Polar Projection in a Rectangular Box
Next, we will create a polar projection in a rectangular box using GridHelperCurveLinear. We will use an Affine2D transform to scale the degree coordinates to radians, and PolarAxes.PolarTransform to create the polar projection. We will also use angle_helper.ExtremeFinderCycle to find the extremes of the polar projection, and angle_helper.LocatorDMS and angle_helper.FormatterDMS to format the tick labels. The following code demonstrates this process:
def curvelinear_test2(fig):
# Define the custom transform
tr = Affine2D().scale(np.pi/180, 1) + PolarAxes.PolarTransform()
# Define the extreme finder, grid locator, and tick formatter
extreme_finder = angle_helper.ExtremeFinderCycle(
nx=20, ny=20,
lon_cycle=360, lat_cycle=None,
lon_minmax=None, lat_minmax=(0, np.inf),
)
grid_locator1 = angle_helper.LocatorDMS(12)
tick_formatter1 = angle_helper.FormatterDMS()
# Create GridHelperCurveLinear object
grid_helper = GridHelperCurveLinear(
tr, extreme_finder=extreme_finder,
grid_locator1=grid_locator1, tick_formatter1=tick_formatter1)
ax1 = fig.add_subplot(
1, 2, 2, axes_class=HostAxes, grid_helper=grid_helper)
# Make ticklabels of right and top axis visible
ax1.axis["right"].major_ticklabels.set_visible(True)
ax1.axis["top"].major_ticklabels.set_visible(True)
# Let right axis show ticklabels for 1st coordinate (angle)
ax1.axis["right"].get_helper().nth_coord_ticks = 0
# Let bottom axis show ticklabels for 2nd coordinate (radius)
ax1.axis["bottom"].get_helper().nth_coord_ticks = 1
# Set the aspect ratio and limits of the subplot
ax1.set_aspect(1)
ax1.set_xlim(-5, 12)
ax1.set_ylim(-5, 10)
# Add grid lines to the subplot
ax1.grid(True, zorder=0)
# Create a parasite axes with the given transform
ax2 = ax1.get_aux_axes(tr)
# Anything you draw in ax2 will match the ticks and grids of ax1.
ax2.plot(np.linspace(0, 30, 51), np.linspace(10, 10, 51), linewidth=2)
ax2.pcolor(np.linspace(0, 90, 4), np.linspace(0, 10, 4),
np.arange(9).reshape((3, 3)))
ax2.contour(np.linspace(0, 90, 4), np.linspace(0, 10, 4),
np.arange(16).reshape((4, 4)), colors="k")
fig = plt.figure(figsize=(7, 4))
curvelinear_test2(fig)
plt.show()
Final Code
The final code combines the code from Step 1 and Step 2:
import matplotlib.pyplot as plt
import numpy as np
from matplotlib.projections import PolarAxes
from matplotlib.transforms import Affine2D
from mpl_toolkits.axisartist import Axes, HostAxes, angle_helper
from mpl_toolkits.axisartist.grid_helper_curvelinear import GridHelperCurveLinear
def curvelinear_test1(fig):
# Define custom transform
def tr(x, y):
return x, y - x
def inv_tr(x, y):
return x, y + x
# Create GridHelperCurveLinear object
grid_helper = GridHelperCurveLinear((tr, inv_tr))
# Create a subplot with the custom grid and tick lines
ax1 = fig.add_subplot(1, 2, 1, axes_class=Axes, grid_helper=grid_helper)
# Plot some points on the subplot
xx, yy = tr(np.array([3, 6]), np.array([5, 10]))
ax1.plot(xx, yy)
# Set the aspect ratio and limits of the subplot
ax1.set_aspect(1)
ax1.set_xlim(0, 10)
ax1.set_ylim(0, 10)
# Add floating axes and grid lines
ax1.axis["t"] = ax1.new_floating_axis(0, 3)
ax1.axis["t2"] = ax1.new_floating_axis(1, 7)
ax1.grid(True, zorder=0)
def curvelinear_test2(fig):
# Define the custom transform
tr = Affine2D().scale(np.pi/180, 1) + PolarAxes.PolarTransform()
# Define the extreme finder, grid locator, and tick formatter
extreme_finder = angle_helper.ExtremeFinderCycle(
nx=20, ny=20,
lon_cycle=360, lat_cycle=None,
lon_minmax=None, lat_minmax=(0, np.inf),
)
grid_locator1 = angle_helper.LocatorDMS(12)
tick_formatter1 = angle_helper.FormatterDMS()
# Create GridHelperCurveLinear object
grid_helper = GridHelperCurveLinear(
tr, extreme_finder=extreme_finder,
grid_locator1=grid_locator1, tick_formatter1=tick_formatter1)
ax1 = fig.add_subplot(
1, 2, 2, axes_class=HostAxes, grid_helper=grid_helper)
# Make ticklabels of right and top axis visible
ax1.axis["right"].major_ticklabels.set_visible(True)
ax1.axis["top"].major_ticklabels.set_visible(True)
# Let right axis show ticklabels for 1st coordinate (angle)
ax1.axis["right"].get_helper().nth_coord_ticks = 0
# Let bottom axis show ticklabels for 2nd coordinate (radius)
ax1.axis["bottom"].get_helper().nth_coord_ticks = 1
# Set the aspect ratio and limits of the subplot
ax1.set_aspect(1)
ax1.set_xlim(-5, 12)
ax1.set_ylim(-5, 10)
# Add grid lines to the subplot
ax1.grid(True, zorder=0)
# Create a parasite axes with the given transform
ax2 = ax1.get_aux_axes(tr)
# Anything you draw in ax2 will match the ticks and grids of ax1.
ax2.plot(np.linspace(0, 30, 51), np.linspace(10, 10, 51), linewidth=2)
ax2.pcolor(np.linspace(0, 90, 4), np.linspace(0, 10, 4),
np.arange(9).reshape((3, 3)))
ax2.contour(np.linspace(0, 90, 4), np.linspace(0, 10, 4),
np.arange(16).reshape((4, 4)), colors="k")
fig = plt.figure(figsize=(7, 4))
curvelinear_test1(fig)
curvelinear_test2(fig)
plt.show()
Summary
In this lab, we learned how to create custom grid and tick lines using GridHelperCurveLinear. We also learned how to create a polar projection in a rectangular box using Affine2D, PolarAxes.PolarTransform, and GridHelperCurveLinear.
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