__init__.py 文件源码

def tissot(self,lon_0,lat_0,radius_deg,npts,ax=None,**kwargs):
        """
        Draw a polygon centered at ``lon_0,lat_0``.  The polygon
        approximates a circle on the surface of the earth with radius
        ``radius_deg`` degrees latitude along longitude ``lon_0``,
        made up of ``npts`` vertices.
        The polygon represents a Tissot's indicatrix
        (http://en.wikipedia.org/wiki/Tissot's_Indicatrix),
        which when drawn on a map shows the distortion
        inherent in the map projection.

        .. note::
         Cannot handle situations in which the polygon intersects
         the edge of the map projection domain, and then re-enters the domain.

        Extra keyword ``ax`` can be used to override the default axis instance.

        Other \**kwargs passed on to matplotlib.patches.Polygon.

        returns a matplotlib.patches.Polygon object."""
        ax = kwargs.pop('ax', None) or self._check_ax()
        g = pyproj.Geod(a=self.rmajor,b=self.rminor)
        az12,az21,dist = g.inv(lon_0,lat_0,lon_0,lat_0+radius_deg)
        seg = [self(lon_0,lat_0+radius_deg)]
        delaz = 360./npts
        az = az12
        for n in range(npts):
            az = az+delaz
            lon, lat, az21 = g.fwd(lon_0, lat_0, az, dist)
            x,y = self(lon,lat)
            # add segment if it is in the map projection region.
            if x < 1.e20 and y < 1.e20:
                seg.append((x,y))
        poly = Polygon(seg,**kwargs)
        ax.add_patch(poly)
        # clip polygons for round polar plots.
        if self.round: poly,c = self._clipcircle(ax,poly)
        # set axes limits to fit map region.
        self.set_axes_limits(ax=ax)
        return poly