Arcs and Ellipses look like polylines

[ghost]

Hi,
In Matplotlib, Ellipses (and Ellipses Arcs) are drawn using Bezier splines, as explained here.
When using Cartopy, it looks to me like the projection of these splines is not so nice as with vanilla Matplotlib.
The last test below gives this image:

Thanks!

import math

from matplotlib import patches
import matplotlib.pyplot as plt

import cartopy.crs as ccrs
from cartopy.io.img_tiles import OSM

def setup_osm():
  osm = OSM()
  proj = osm.crs  
  ax = plt.axes(projection=proj)
  ax.add_image(osm, 5)
  return ax
  
def setup_stock_img():
  ax = plt.axes(projection=ccrs.PlateCarree())
  ax.stock_img()
  return ax

def plot_arc(ax):
  ax.add_patch(patches.Arc(
      (2.0, 44.0), 
      width = 2.0 / math.cos(math.radians(44.0)),
      height = 2.0,
      angle = 0.0,
      theta1= 90.0,
      theta2= 180.0,
      fill=False,
      linewidth=2,
      transform=ccrs.Geodetic()))
  ax.set_extent((-2.0, 4.0, 41.0, 47.0))
  plt.show()
  
def plot_ellipse(ax):
  ax.add_patch(patches.Ellipse(
      (2.0, 44.0), 
      width = 2.0 / math.cos(math.radians(44.0)),
      height = 2.0,
      angle = 0.0,
      fill=False,
      linewidth=2,
      transform=ccrs.Geodetic()))
  ax.set_extent((0.0, 4.0, 42.0, 46.0))
  plt.show()  

plot_arc(setup_stock_img())
plot_arc(setup_osm())
plot_ellipse(setup_osm())

[ResidentMario]

+1 to this. This effect is obvious and rather undesirable here also, in the cartopy example gallery.

[kaspervanwijk]

I had noticed the behaviour as well, and resorted to using tissot, instead, for smooth circles on maps. This does not help if you need ellipses, though.

[ajdawson]

This seems to be a problem with how the arcs/ellipses are represented and drawn after a projection. If there is no projection transform the objects appear as expected. This is not simply due to a poor choice of projection threshold.

@ResidentMario - The example gallery problem is actually slightly different to the problem here, although it looks the same, it is to do with the projection threshold being too large.

[pelson]

Came up in https://stackoverflow.com/questions/54192575/matplotlib-circle-patch-does-not-have-smooth-edges.
I've been working on a Path interpolator that would allow us to fine-tune the path as we zoom in (in matplotlib). Might prove to be a really workable solution for this problem.

[kaspervanwijk]

Unable to solve this myself, I ended up using the tissot function <https://matplotlib.org/basemap/api/basemap_api.html#mpl_toolkits.basemap.Basemap.tissot>, instead, as I only needed circles...

…

On Wed, 16 Jan 2019 at 03:28, Phil Elson ***@***.***> wrote: Came up in https://stackoverflow.com/questions/54192575/matplotlib-circle-patch-does-not-have-smooth-edges . I've been working on a Path interpolator that would allow us to fine-tune the path as we zoom in (in matplotlib). Might prove to be a really workable solution for this problem. — You are receiving this because you commented. Reply to this email directly, view it on GitHub <#825 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AE253lEL_r5wrEGeY8b3bo4LerqJNZwHks5vDeWZgaJpZM4LIeNV> .

[sergio-dr]

Is there any workaround for ellipses? (I'm using PlateCarree). Thanks