[Matplotlib-users] basemap: how to plot "toothed" curves

[Phil Cummins]

Hi,

I would like to plot "toothed" curves using basemap. These are curves
with triangles on one side, that are used to plot pressure fronts in
meteorology or thrust faults in geology. You need to be able to say
which side of the curve the triangles should appear on. Does anyone know
whether such curves can be plotted using mtplotlib/basemap?

Thanks,

- Phil

Australian National University

[Benjamin Root]

Hmmm, this is actually an interesting problem. I am also a meteorologist,
so this is interesting to me.

I haven't figured it out yet, but here are my thoughts:

1) There are the "^" triangle markers as well as "2" tri_up markers:
http://nbviewer.ipython.org/github/WeatherGod/AnatomyOfMatplotlib/blob/master/AnatomyOfMatplotlib-Part3-HowToSpeakMPL.ipynb#Markers
2) The markevery property should be set to a float value to have the
markers spaced out evenly along the line regardless of aspect ratios and
zooming (note, this assumes that the line is defined with many vertices to
give a smooth appearance).

Problem:
Using markers and markevery in a Line2D object has an inherent limitation:
all of the markers will be drawn in the same orientation. So, we can't
orient the markers along the normal of the line.
Also, there is no pre-defined marker for half-circles, so this approach
wouldn't work well for warm-fronts/dry-lines/etc.

I'll have to see if a PolygonCollection + Line2D might be the right
approach here...

Ben Root

Hi,
I would like to plot "toothed" curves using basemap. These are curves with
triangles on one side, that are used to plot pressure fronts in meteorology
or thrust faults in geology. You need to be able to say which side of the
curve the triangles should appear on. Does anyone know whether such curves
can be plotted using mtplotlib/basemap?
Thanks,
- Phil
Australian National University
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[Benjamin Root]

Looks like someone else figured out a creative solution using quiver:
http://stackoverflow.com/questions/19918502/sawtooth-line-style-in-matplotlib

Here it is (slightly cleaned up):

import matplotlib.pyplot as pltimport numpy as np

x = np.linspace(0, 2*np.pi, 100)
y = np.sin(x)

dx = np.diff(x)
dy = np.diff(y)

x2 = np.linspace(0, 2*np.pi, 10)
y2 = np.sin(x2)

dx = np.zeros_like(x2) + 1e-12
dy = np.sin(x2 + dx) - y2

length = np.hypot(dx, dy)
dx /= length
dy /= length

fig, ax = plt.subplots()
ax.set_aspect("equal")
ax.plot(x, y, lw=4)

size = 20
ax.quiver(x2, y2, -dy, dx, headaxislength=size, headlength=size,
headwidth=size, color="blue")
plt.margins(0.2)


I don't know yet how to get rounded heads, though. Now I am looking to see
how the text box styles of "sawtooth" and "roundtooth" are handled in the
code to see if that could be exploited, instead.

Cheers!
Ben Root

Post by Benjamin Root
Hmmm, this is actually an interesting problem. I am also a meteorologist,
so this is interesting to me.
http://nbviewer.ipython.org/github/WeatherGod/AnatomyOfMatplotlib/blob/master/AnatomyOfMatplotlib-Part3-HowToSpeakMPL.ipynb#Markers
2) The markevery property should be set to a float value to have the
markers spaced out evenly along the line regardless of aspect ratios and
zooming (note, this assumes that the line is defined with many vertices to
give a smooth appearance).
all of the markers will be drawn in the same orientation. So, we can't
orient the markers along the normal of the line.
Also, there is no pre-defined marker for half-circles, so this approach
wouldn't work well for warm-fronts/dry-lines/etc.
I'll have to see if a PolygonCollection + Line2D might be the right
approach here...
Ben Root

Post by Phil Cummins
Hi,
I would like to plot "toothed" curves using basemap. These are curves
with triangles on one side, that are used to plot pressure fronts in
meteorology or thrust faults in geology. You need to be able to say which
side of the curve the triangles should appear on. Does anyone know whether
such curves can be plotted using mtplotlib/basemap?
Thanks,
- Phil
Australian National University
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[Phil Cummins]

Wow, that's fantastic Ben. Thanks so much for finding that, it's just
what I need!
Regards,

- Phil

Post by Benjamin Root
http://stackoverflow.com/questions/19918502/sawtooth-line-style-in-matplotlib
|import matplotlib.pyplotas plt
import numpyas np
x= np.linspace(0, 2*np.pi, 100)
y= np.sin(x)
dx= np.diff(x)
dy= np.diff(y)
x2= np.linspace(0, 2*np.pi, 10)
y2= np.sin(x2)
dx= np.zeros_like(x2) + 1e-12
dy= np.sin(x2+dx) - y2
length= np.hypot(dx,dy)
dx/= length
dy/= length
fig, ax= plt.subplots()
ax.set_aspect("equal")
ax.plot(x, y, lw=4)
size= 20
ax.quiver(x2, y2, -dy, dx, headaxislength=size, headlength=size, headwidth=size, color="blue")
plt.margins(0.2)|
I don't know yet how to get rounded heads, though. Now I am looking to
see how the text box styles of "sawtooth" and "roundtooth" are handled
in the code to see if that could be exploited, instead.
Cheers!
Ben Root
Hmmm, this is actually an interesting problem. I am also a
meteorologist, so this is interesting to me.
http://nbviewer.ipython.org/github/WeatherGod/AnatomyOfMatplotlib/blob/master/AnatomyOfMatplotlib-Part3-HowToSpeakMPL.ipynb#Markers
2) The markevery property should be set to a float value to have
the markers spaced out evenly along the line regardless of aspect
ratios and zooming (note, this assumes that the line is defined
with many vertices to give a smooth appearance).
Using markers and markevery in a Line2D object has an inherent
limitation: all of the markers will be drawn in the same
orientation. So, we can't orient the markers along the normal of
the line.
Also, there is no pre-defined marker for half-circles, so this
approach wouldn't work well for warm-fronts/dry-lines/etc.
I'll have to see if a PolygonCollection + Line2D might be the
right approach here...
Ben Root
On Fri, Oct 16, 2015 at 7:22 AM, Phil Cummins
Hi,
I would like to plot "toothed" curves using basemap. These are
curves with triangles on one side, that are used to plot
pressure fronts in meteorology or thrust faults in geology.
You need to be able to say which side of the curve the
triangles should appear on. Does anyone know whether such
curves can be plotted using mtplotlib/basemap?
Thanks,
- Phil
Australian National University
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