Hello, first of all: thanks for the great software!! After the years of struggling with gnuplot, i really enjoy making my graphs with matplotlib. I'd like to ask, if it is possible to create a contour graph using polar coordinates? If not, can someone give me some pointers about how to implement it? Kind regards, Petr Danecek
Petr Danecek wrote: > Hello, > first of all: thanks for the great software!! After the years of > struggling with gnuplot, i really enjoy making my graphs with > matplotlib. > > I'd like to ask, if it is possible to create a contour graph using polar > coordinates? If not, can someone give me some pointers about how to > implement it? > > Kind regards, > Petr Danecek > > Petr: I don't think contour directly supports polar axes, but if your data are in polar coordinates you can easily make a contour plot with cartesian axes, like this: from pylab import * deltatheta = 2.*pi/100. theta = arange(0.,2.*pi,deltatheta) R = arange(0.,pi,deltatheta) r,t = meshgrid(R, theta) Z = sin(r)*sin(3.*t) X = r*cos(t) Y = r*sin(t) cs = contourf(X,Y,Z) show() -Jeff -- Jeffrey S. Whitaker Phone : (303)497-6313 Meteorologist FAX : (303)497-6449 NOAA/OAR/PSD R/PSD1 Email : Jef...@no... 325 Broadway Office : Skaggs Research Cntr 1D-124 Boulder, CO, USA 80303-3328 Web : http://tinyurl.com/5telg
Petr Danecek wrote:
> Hello,
> first of all: thanks for the great software!! After the years of
> struggling with gnuplot, i really enjoy making my graphs with
> matplotlib.
>
> I'd like to ask, if it is possible to create a contour graph using polar
> coordinates? If not, can someone give me some pointers about how to
> implement it?
>
> Kind regards,
> Petr Danecek
>
>
>
Here's a slightly prettier version of my previous example:
from pylab import *
deltatheta = 2.*pi/100.
theta = arange(0.,2.*pi+0.5*deltatheta,deltatheta)
R = arange(0.,pi,deltatheta)
r,t = meshgrid(R, theta)
Z = sin(r)*sin(3.*t)
X = r*cos(t)
Y = r*sin(t)
ax = subplot(111)
cs = ax.contourf(X,Y,Z)
# make sure aspect ratio preserved
ax.set_aspect('equal')
# turn off rectangular frame.
ax.set_frame_on(False)
# turn off axis ticks.
ax.set_xticks([])
ax.set_yticks([])
# draw a circle around the edge of the plot.
rmax = max(R)
ax.plot(rmax*cos(theta),rmax*sin(theta),'k')
title('Polar contours')
show()
--
Jeffrey S. Whitaker Phone : (303)497-6313
Meteorologist FAX : (303)497-6449
NOAA/OAR/PSD R/PSD1 Email : Jef...@no...
325 Broadway Office : Skaggs Research Cntr 1D-124
Boulder, CO, USA 80303-3328 Web : http://tinyurl.com/5telg
Beautiful! The grid lines must be drawn manually?
On Thu, 2006年12月28日 at 13:32 -0700, Jeff Whitaker wrote:
> Here's a slightly prettier version of my previous example:
>
> from pylab import *
> deltatheta = 2.*pi/100.
> theta = arange(0.,2.*pi+0.5*deltatheta,deltatheta)
> R = arange(0.,pi,deltatheta)
> r,t = meshgrid(R, theta)
> Z = sin(r)*sin(3.*t)
> X = r*cos(t)
> Y = r*sin(t)
> ax = subplot(111)
> cs = ax.contourf(X,Y,Z)
> # make sure aspect ratio preserved
> ax.set_aspect('equal')
> # turn off rectangular frame.
> ax.set_frame_on(False)
> # turn off axis ticks.
> ax.set_xticks([])
> ax.set_yticks([])
> # draw a circle around the edge of the plot.
> rmax = max(R)
> ax.plot(rmax*cos(theta),rmax*sin(theta),'k')
> title('Polar contours')
> show()
>
Petr Danecek wrote:
> Beautiful! The grid lines must be drawn manually?
>
> On Thu, 2006年12月28日 at 13:32 -0700, Jeff Whitaker wrote:
>
>> Here's a slightly prettier version of my previous example:
>>
>> from pylab import *
>> deltatheta = 2.*pi/100.
>> theta = arange(0.,2.*pi+0.5*deltatheta,deltatheta)
>> R = arange(0.,pi,deltatheta)
>> r,t = meshgrid(R, theta)
>> Z = sin(r)*sin(3.*t)
>> X = r*cos(t)
>> Y = r*sin(t)
>> ax = subplot(111)
>> cs = ax.contourf(X,Y,Z)
>> # make sure aspect ratio preserved
>> ax.set_aspect('equal')
>> # turn off rectangular frame.
>> ax.set_frame_on(False)
>> # turn off axis ticks.
>> ax.set_xticks([])
>> ax.set_yticks([])
>> # draw a circle around the edge of the plot.
>> rmax = max(R)
>> ax.plot(rmax*cos(theta),rmax*sin(theta),'k')
>> title('Polar contours')
>> show()
>>
>>
>
>
Petr: Yes. matplotlib has polar axes for some kinds of plots, but not
for contour plots.
-Jeff
--
Jeffrey S. Whitaker Phone : (303)497-6313
NOAA/OAR/CDC R/PSD1 FAX : (303)497-6449
325 Broadway Boulder, CO, USA 80305-3328
Petr Danecek wrote:
> Beautiful! The grid lines must be drawn manually?
>
> On Thu, 2006年12月28日 at 13:32 -0700, Jeff Whitaker wrote:
>
>> Here's a slightly prettier version of my previous example:
>>
>> from pylab import *
>> deltatheta = 2.*pi/100.
>> theta = arange(0.,2.*pi+0.5*deltatheta,deltatheta)
>> R = arange(0.,pi,deltatheta)
>> r,t = meshgrid(R, theta)
>> Z = sin(r)*sin(3.*t)
>> X = r*cos(t)
>> Y = r*sin(t)
>> ax = subplot(111)
>> cs = ax.contourf(X,Y,Z)
>> # make sure aspect ratio preserved
>> ax.set_aspect('equal')
>> # turn off rectangular frame.
>> ax.set_frame_on(False)
>> # turn off axis ticks.
>> ax.set_xticks([])
>> ax.set_yticks([])
>> # draw a circle around the edge of the plot.
>> rmax = max(R)
>> ax.plot(rmax*cos(theta),rmax*sin(theta),'k')
>> title('Polar contours')
>> show()
>>
>>
Petr: Another option might be to use pcolor, it does work wit polar axes.
import pylab
# make color-filled plot of polar coordinate data array.
# define coordinates.
theta = pylab.linspace(0.,2.*pylab.pi,101)
R = pylab.linspace(0.,pylab.pi,101)
Y,X = pylab.meshgrid(R, theta)
# data to plot.
Z = pylab.sin(Y)*pylab.sin(4*X) + pylab.exp(-(Y**2/4))
# create subplot.
ax = pylab.subplot(111,polar=True)
# mesh fill.
ax.pcolormesh(X,Y,Z)
# make sure aspect ratio preserved
ax.set_aspect('equal')
pylab.show()
-Jeff
--
Jeffrey S. Whitaker Phone : (303)497-6313
NOAA/OAR/CDC R/PSD1 FAX : (303)497-6449
325 Broadway Boulder, CO, USA 80305-3328
Petr Danecek wrote:
> Beautiful! The grid lines must be drawn manually?
>
> On Thu, 2006年12月28日 at 13:32 -0700, Jeff Whitaker wrote:
>
>> Here's a slightly prettier version of my previous example:
>>
>> from pylab import *
>> deltatheta = 2.*pi/100.
>> theta = arange(0.,2.*pi+0.5*deltatheta,deltatheta)
>> R = arange(0.,pi,deltatheta)
>> r,t = meshgrid(R, theta)
>> Z = sin(r)*sin(3.*t)
>> X = r*cos(t)
>> Y = r*sin(t)
>> ax = subplot(111)
>> cs = ax.contourf(X,Y,Z)
>> # make sure aspect ratio preserved
>> ax.set_aspect('equal')
>> # turn off rectangular frame.
>> ax.set_frame_on(False)
>> # turn off axis ticks.
>> ax.set_xticks([])
>> ax.set_yticks([])
>> # draw a circle around the edge of the plot.
>> rmax = max(R)
>> ax.plot(rmax*cos(theta),rmax*sin(theta),'k')
>> title('Polar contours')
>> show()
>>
>>
>
>
Petr: Here's yet another way to do it, using the basemap toolkit. This
way you get axis grid lines.
from matplotlib.toolkits.basemap import Basemap
import pylab
theta = pylab.linspace(0.,2.*pylab.pi,101)
R = pylab.linspace(0.,pylab.pi,101)
lat,lon = pylab.meshgrid(R, theta)
Z = pylab.sin(lat)*pylab.sin(4*lon) + pylab.exp(-(lat**2/4))
# convert radial coordinate to latitude, with r=0 being north pole
# and r=rmax being equator.
# convert r and theta to degrees.
lat = (180./pylab.pi)*0.5*lat[::-1,:]
lon = (180./pylab.pi)*lon
m = Basemap(boundinglat=0.,lon_0=0.,resolution=None,projection='npaeqd')
X,Y = m(lon,lat)
CS = m.contourf(X,Y,Z,15)
m.drawparallels(pylab.arange(0,90,20),labels=[1,1,1,1])
m.drawmeridians(pylab.arange(0,360,60),labels=[1,1,1,1])
pylab.show()
-Jeff
--
Jeffrey S. Whitaker Phone : (303)497-6313
NOAA/OAR/CDC R/PSD1 FAX : (303)497-6449
325 Broadway Boulder, CO, USA 80305-3328
Petr Danecek wrote: > Hello, > first of all: thanks for the great software!! After the years of > struggling with gnuplot, i really enjoy making my graphs with > matplotlib. > > I'd like to ask, if it is possible to create a contour graph using polar > coordinates? If not, can someone give me some pointers about how to > implement it? John has said that he plans to improve polar coordinate handling in the next month or two. If it turns out that changes are also needed in contour.py, I will be happy to make them. So, if all goes well, within a few months we should have contouring and other things working well with polar coordinates. In the meantime, I am glad Jeff has provided a workaround. (I took a stab at making contouring work to a useful degree with present polar coordinates--given that pcolor works, it should be possible--but I couldn't quite get it. Maybe I will try again later.) Eric