Basemap/ orthographic projection plot doesn't respect globe boundary

Hi forum/ mailing list,
When I plot in the orthographic projection I’m getting the large artefact shown below extending away from the north east of the globe.
I’m not finding the same problem when plotting in a full globe projection so I’m presuming the problem is with the way I’m projecting everything rather than my data itself.
I’ve included my plotting code below, if anyone is able to spot some glaring omissions/ errors I’d be most grateful (I’ve been using python/ matplotlib for only a couple of weeks now!).

import numpy as np
import matplotlib.pyplot as plt
from mpl_toolkits.basemap import Basemap
import sys, glob

#input must be 3 col file of lons lats and data
#bins input values into half degree grid, ignores negative values

plts = glob.glob(’*.plt’)
x = np.arange(-180, 180, 0.5); y = np.arange(-90, 90, 0.5)
grid_lon, grid_lat = np.meshgrid(x,y) #regularly spaced 2D grid
n_vals = np.zeros((360,720)) #mean divisor
dat = np.zeros((360,720)) #2D grid of zeros

for pt in plts:

in_file = pt
data = np.loadtxt(in_file, comments = ';')
fname = in_file.split('.')[0]

lon = data[:,0] #original 1D list
lat = data[:,1] #original 1D list
slcol = data[:,2] #z data

lon = (np.around(lon*2))/2 #round to nearest .0 or 0.5
lat = (np.around(lat*2))/2 #round to nearest .0 or 0.5

##keep the below between files


for i in slcol:
    if lon[j] < 0:
        grid_lon_ind = 360+(lon[j]*2)
        grid_lat_ind = 180+(lat[j]*2)
        grid_lon_ind = 360-(lon[j]*2)
        grid_lat_ind = 180+(lat[j]*2)

    if i > 0:
        dat[grid_lat_ind, grid_lon_ind] += i #add i'th value
        n_vals[grid_lat_ind, grid_lon_ind] += 1 #increase cell counter by 1 for each extra value

dat = np.nan_to_num(dat/n_vals)

#create map object
fig = plt.figure()
m = Basemap(projection=‘ortho’, lon_0=lon[(len(lon)/2)], lat_0=0, resolution=‘l’, area_thresh=10000.)
#m = Basemap(projection=‘moll’,lon_0=0,resolution=‘c’, area_thresh=10000.)

X,Y = m(grid_lon, grid_lat)

#pass all 2d arrays to pcolor
im = m.pcolormesh(X,Y,dat)

#add coastlines, globe boundary and colourbar
m.drawparallels(np.arange(-90, 90,30))

plt.title(‘CH20 and ting’)

Thanks for your help,



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