importnumpyasnpimportmatplotlib.pyplotaspltfrommpl_toolkits.axisartistimportSubplotHostfrommpl_toolkits.axisartist.grid_helper_curvelinearimportGridHelperCurveLinearimportmpl_toolkits.axisartist.angle_helperasangle_helperfrommatplotlib.projectionsimportPolarAxesfrommatplotlib.transformsimportAffine2DclassFormatterDMS(object):'''Transforms angle ticks to damping ratios'''def__call__(self,direction,factor,values):angles_deg=values/factordamping_ratios=np.cos((180-angles_deg)*np.pi/180)ret= ["%.2f"%valforvalindamping_ratios]returnretclassModifiedExtremeFinderCycle(angle_helper.ExtremeFinderCycle):'''Changed to allow only left hand-side polar grid'''def__call__(self,transform_xy,x1,y1,x2,y2):x_,y_=np.linspace(x1,x2,self.nx),np.linspace(y1,y2,self.ny)x,y=np.meshgrid(x_,y_)lon,lat=transform_xy(np.ravel(x),np.ravel(y))withnp.errstate(invalid='ignore'):ifself.lon_cycleisnotNone:lon0=np.nanmin(lon)lon-=360.* ((lon-lon0)>360.)# Changed from 180 to 360 to be able to span only 90-270 (left hand side)ifself.lat_cycleisnotNone:lat0=np.nanmin(lat)lat-=360.* ((lat-lat0)>360.)# Changed from 180 to 360 to be able to span only 90-270 (left hand side)lon_min,lon_max=np.nanmin(lon),np.nanmax(lon)lat_min,lat_max=np.nanmin(lat),np.nanmax(lat)lon_min,lon_max,lat_min,lat_max= \self._adjust_extremes(lon_min,lon_max,lat_min,lat_max)returnlon_min,lon_max,lat_min,lat_maxdefsgrid():# From matplotlib demos:# https://matplotlib.org/gallery/axisartist/demo_curvelinear_grid.html# https://matplotlib.org/gallery/axisartist/demo_floating_axis.html# PolarAxes.PolarTransform takes radian. However, we want our coordinate# system in degreetr=Affine2D().scale(np.pi/180.,1.)+PolarAxes.PolarTransform()# polar projection, which involves cycle, and also has limits in# its coordinates, needs a special method to find the extremes# (min, max of the coordinate within the view).# 20, 20 : number of sampling points along x, y directionsampling_points=20extreme_finder=ModifiedExtremeFinderCycle(sampling_points,sampling_points,lon_cycle=360,lat_cycle=None,lon_minmax=(90,270),lat_minmax=(0,np.inf),)grid_locator1=angle_helper.LocatorDMS(15)tick_formatter1=FormatterDMS()grid_helper=GridHelperCurveLinear(tr,extreme_finder=extreme_finder,grid_locator1=grid_locator1,tick_formatter1=tick_formatter1                                        )fig=plt.figure()ax=SubplotHost(fig,1,1,1,grid_helper=grid_helper)# make ticklabels of right invisible, and top axis visible.visible=Trueax.axis[:].major_ticklabels.set_visible(visible)ax.axis[:].major_ticks.set_visible(False)ax.axis[:].invert_ticklabel_direction()ax.axis["wnxneg"]=axis=ax.new_floating_axis(0,180)axis.set_ticklabel_direction("-")axis.label.set_visible(False)# let left axis shows ticklabels for 1st coordinate (angle)ax.axis["left"].get_helper().nth_coord_ticks=0ax.axis["right"].get_helper().nth_coord_ticks=0ax.axis["left"].get_helper().nth_coord_ticks=0ax.axis["bottom"].get_helper().nth_coord_ticks=0fig.add_subplot(ax)ax.grid(True,zorder=0,linestyle='dotted')returnax,figax,f=sgrid()ax.plot([-5,5],[-5,5])

    par2 = ax.twin()    new_fixed_axis = par2.get_grid_helper().new_fixed_axis    par2.axis["left"] = new_fixed_axis(loc="left",                                       axes=par2,                                       offset=(0, 0))    par2.axis["bottom"] = new_fixed_axis(loc="bottom",                                       axes=par2,                                       offset=(0, 0))