## matplotlib-users

 [Matplotlib-users] Polar plot From: jan gillis - 2008-09-16 23:00:59 ```Hello, I have a problem with polar plot, if i run the following code in matplotlib 0.98.3, polar plot is drawing a extra circle to go from angle -3.14159265 to angle 3.03753126. Is there a solution for this problem? ******************** import numpy as np from matplotlib.pyplot import figure, show, rc, grid # radar green, solid grid lines rc('grid', color='#316931', linewidth=1, linestyle='-') rc('xtick', labelsize=15) rc('ytick', labelsize=15) # force square figure and square axes looks better for polar, IMO fig = figure(figsize=(8,8)) ax = fig.add_axes([0.1, 0.1, 0.8, 0.8], polar=True, axisbg='#d5de9c') z = np.zeros((1,2000),complex) z.real = 0.2 z.imag = np.arange(-50,50,0.05) gamma_r = np.transpose((z-1)/(z+1)) ax.plot(np.angle(gamma_r), np.abs(gamma_r), '.-', zorder=0) ax.set_rmax(2.0) grid(True) show() ******************** Kind regards, Jean -- Jan Gillis Ghent University IMEC vzw - INTEC Sint-Pietersnieuwstraat 41 B-9000 Gent Belgium tel. +32 9 264 33 33 jan.gillis@... ```
 Re: [Matplotlib-users] Polar plot From: Tony S Yu - 2008-09-17 09:26:13 ```On Sep 17, 2008, at 1:59 AM, jan gillis wrote: > Hello, > > I have a problem with polar plot, if i run the following code in > matplotlib 0.98.3, polar plot is drawing a extra circle to go from > angle -3.14159265 to angle 3.03753126. Is there a solution for this > problem? > > ******************** > import numpy as np > from matplotlib.pyplot import figure, show, rc, grid > > # radar green, solid grid lines > rc('grid', color='#316931', linewidth=1, linestyle='-') > rc('xtick', labelsize=15) > rc('ytick', labelsize=15) > > # force square figure and square axes looks better for polar, IMO > fig = figure(figsize=(8,8)) > ax = fig.add_axes([0.1, 0.1, 0.8, 0.8], polar=True, axisbg='#d5de9c') > > z = np.zeros((1,2000),complex) > z.real = 0.2 > z.imag = np.arange(-50,50,0.05) > gamma_r = np.transpose((z-1)/(z+1)) > > ax.plot(np.angle(gamma_r), np.abs(gamma_r), '.-', zorder=0) Hi Jan, It looks like you get the circle because the angles you're plotting go from negative to positive radians in a weird way. The circle being drawn starts around 0 radians and goes clockwise by negative values. Then when it gets to - pi, it switches to positive indices, i.e. pi. Of course, these are the same points on a polar plot, but different angles, if you want to be consistent. Here are a couple of quick solutions, but there but there maybe better ways of handling this. # ~~~~~~~~~~~~~~~~~~ # get rid of the plot line above, and add the following theta = np.angle(gamma_r) mag = np.abs(gamma_r) # option 1 ordered = np.argsort(theta, axis=0).squeeze() ax.plot(theta[ordered], mag[ordered], '.-', zorder=0) # option 2 neg_theta = np.where(theta < 0) theta[neg_theta] += 2 * np.pi ax.plot(theta, mag, '.-', zorder=0) # ~~~~~~~~~~~~~~~~~~ I hope that's helpful, -Tony > > ax.set_rmax(2.0) > grid(True) > > show() > > ******************** > Kind regards, > Jean > > -- > Jan Gillis > Ghent University > IMEC vzw - INTEC > Sint-Pietersnieuwstraat 41 > B-9000 Gent > Belgium > tel. +32 9 264 33 33 > jan.gillis@... > > > ------------------------------------------------------------------------- > This SF.Net email is sponsored by the Moblin Your Move Developer's > challenge > Build the coolest Linux based applications with Moblin SDK & win > great prizes > Grand prize is a trip for two to an Open Source event anywhere in > the world > http://moblin-contest.org/redirect.php?banner_id=100&url=/ > _______________________________________________ > Matplotlib-users mailing list > Matplotlib-users@... > https://lists.sourceforge.net/lists/listinfo/matplotlib-users ```
 Re: [Matplotlib-users] Polar plot From: jan gillis - 2008-09-17 23:18:03 ```Hi Tony, Thank you for the reply, the solutions you propose are fine in this case. But I'm trying to use the polar plot as a smith chart for an instrument and there i will receive data that is unknown but can be something like this: r = np.transpose(.1+np.arange ( 0 , 0.7 , 0.001)) theta = -4.5 * np.pi *r freq = r*10e9 data = np.multiply(r,np.exp(1j*theta)) ax.plot(angle(data),abs(data)) Any idea why Polar plot can't handle theta going from negative to positive radians? Jan Tony S Yu wrote: > > On Sep 17, 2008, at 1:59 AM, jan gillis wrote: > >> Hello, >> >> I have a problem with polar plot, if i run the following code in >> matplotlib 0.98.3, polar plot is drawing a extra circle to go from >> angle -3.14159265 to angle 3.03753126. Is there a solution for this >> problem? >> >> ******************** >> import numpy as np >> from matplotlib.pyplot import figure, show, rc, grid >> >> # radar green, solid grid lines >> rc('grid', color='#316931', linewidth=1, linestyle='-') >> rc('xtick', labelsize=15) >> rc('ytick', labelsize=15) >> >> # force square figure and square axes looks better for polar, IMO >> fig = figure(figsize=(8,8)) >> ax = fig.add_axes([0.1, 0.1, 0.8, 0.8], polar=True, axisbg='#d5de9c') >> >> z = np.zeros((1,2000),complex) >> z.real = 0.2 >> z.imag = np.arange(-50,50,0.05) >> gamma_r = np.transpose((z-1)/(z+1)) >> >> ax.plot(np.angle(gamma_r), np.abs(gamma_r), '.-', zorder=0) > > Hi Jan, > > It looks like you get the circle because the angles you're plotting go > from negative to positive radians in a weird way. The circle being > drawn starts around 0 radians and goes clockwise by negative values. > Then when it gets to - pi, it switches to positive indices, i.e. pi. > Of course, these are the same points on a polar plot, but different > angles, if you want to be consistent. > > Here are a couple of quick solutions, but there but there maybe better > ways of handling this. > > # ~~~~~~~~~~~~~~~~~~ > # get rid of the plot line above, and add the following > theta = np.angle(gamma_r) > mag = np.abs(gamma_r) > > # option 1 > ordered = np.argsort(theta, axis=0).squeeze() > ax.plot(theta[ordered], mag[ordered], '.-', zorder=0) > > # option 2 > neg_theta = np.where(theta < 0) > theta[neg_theta] += 2 * np.pi > ax.plot(theta, mag, '.-', zorder=0) > # ~~~~~~~~~~~~~~~~~~ > > I hope that's helpful, > -Tony > >> >> ax.set_rmax(2.0) >> grid(True) >> >> show() >> >> ******************** >> Kind regards, >> Jean >> >> >> ------------------------------------------------------------------------- >> >> This SF.Net email is sponsored by the Moblin Your Move Developer's >> challenge >> Build the coolest Linux based applications with Moblin SDK & win >> great prizes >> Grand prize is a trip for two to an Open Source event anywhere in the >> world >> http://moblin-contest.org/redirect.php?banner_id=100&url=/ >> _______________________________________________ >> Matplotlib-users mailing list >> Matplotlib-users@... >> https://lists.sourceforge.net/lists/listinfo/matplotlib-users > > ```
 Re: [Matplotlib-users] Polar plot From: Michael Droettboom - 2008-09-18 06:16:30 ```It seems you're getting bitten by the brain-dead interpolation of points (which is meant to draw line segments as curves that follow the radii). I have fixed the polar drawing code in SVN r6106 to normalize theta to (0.0 <= theta <= 2pi) before doing the interpolation, which seems to fix your example. The user doesn't/shouldn't have to care about whether theta is negative. Cheers, Mike jan gillis wrote: > Hi Tony, > > Thank you for the reply, the solutions you propose are fine in this > case. But I'm trying to use the polar plot > as a smith chart for an instrument and there i will receive data that is > unknown but can be something like this: > > r = np.transpose(.1+np.arange ( 0 , 0.7 , 0.001)) > theta = -4.5 * np.pi *r > freq = r*10e9 > data = np.multiply(r,np.exp(1j*theta)) > ax.plot(angle(data),abs(data)) > > Any idea why Polar plot can't handle theta going from negative to > positive radians? > > Jan > > Tony S Yu wrote: > >> On Sep 17, 2008, at 1:59 AM, jan gillis wrote: >> >> >>> Hello, >>> >>> I have a problem with polar plot, if i run the following code in >>> matplotlib 0.98.3, polar plot is drawing a extra circle to go from >>> angle -3.14159265 to angle 3.03753126. Is there a solution for this >>> problem? >>> >>> ******************** >>> import numpy as np >>> from matplotlib.pyplot import figure, show, rc, grid >>> >>> # radar green, solid grid lines >>> rc('grid', color='#316931', linewidth=1, linestyle='-') >>> rc('xtick', labelsize=15) >>> rc('ytick', labelsize=15) >>> >>> # force square figure and square axes looks better for polar, IMO >>> fig = figure(figsize=(8,8)) >>> ax = fig.add_axes([0.1, 0.1, 0.8, 0.8], polar=True, axisbg='#d5de9c') >>> >>> z = np.zeros((1,2000),complex) >>> z.real = 0.2 >>> z.imag = np.arange(-50,50,0.05) >>> gamma_r = np.transpose((z-1)/(z+1)) >>> >>> ax.plot(np.angle(gamma_r), np.abs(gamma_r), '.-', zorder=0) >>> >> Hi Jan, >> >> It looks like you get the circle because the angles you're plotting go >> from negative to positive radians in a weird way. The circle being >> drawn starts around 0 radians and goes clockwise by negative values. >> Then when it gets to - pi, it switches to positive indices, i.e. pi. >> Of course, these are the same points on a polar plot, but different >> angles, if you want to be consistent. >> >> Here are a couple of quick solutions, but there but there maybe better >> ways of handling this. >> >> # ~~~~~~~~~~~~~~~~~~ >> # get rid of the plot line above, and add the following >> theta = np.angle(gamma_r) >> mag = np.abs(gamma_r) >> >> # option 1 >> ordered = np.argsort(theta, axis=0).squeeze() >> ax.plot(theta[ordered], mag[ordered], '.-', zorder=0) >> >> # option 2 >> neg_theta = np.where(theta < 0) >> theta[neg_theta] += 2 * np.pi >> ax.plot(theta, mag, '.-', zorder=0) >> # ~~~~~~~~~~~~~~~~~~ >> >> I hope that's helpful, >> -Tony >> >> >>> ax.set_rmax(2.0) >>> grid(True) >>> >>> show() >>> >>> ******************** >>> Kind regards, >>> Jean >>> >>> >>> ------------------------------------------------------------------------- >>> >>> This SF.Net email is sponsored by the Moblin Your Move Developer's >>> challenge >>> Build the coolest Linux based applications with Moblin SDK & win >>> great prizes >>> Grand prize is a trip for two to an Open Source event anywhere in the >>> world >>> http://moblin-contest.org/redirect.php?banner_id=100&url=/ >>> _______________________________________________ >>> Matplotlib-users mailing list >>> Matplotlib-users@... >>> https://lists.sourceforge.net/lists/listinfo/matplotlib-users >>> >> > > ------------------------------------------------------------------------- > This SF.Net email is sponsored by the Moblin Your Move Developer's challenge > Build the coolest Linux based applications with Moblin SDK & win great prizes > Grand prize is a trip for two to an Open Source event anywhere in the world > http://moblin-contest.org/redirect.php?banner_id=100&url=/ > _______________________________________________ > Matplotlib-users mailing list > Matplotlib-users@... > https://lists.sourceforge.net/lists/listinfo/matplotlib-users > -- Michael Droettboom Science Software Branch Operations and Engineering Division Space Telescope Science Institute Operated by AURA for NASA ```