def test_geographic_distance(self):
actual = angles.geographic_distance(0., 0., 1., 0.)
expected = 111194.87 # 60 nautical miles in kilometers
self.assertAlmostEqual(actual, expected, 1)
actual = angles.geographic_distance(0., 0.5, 0., -0.5)
self.assertAlmostEqual(actual, expected, 1)
actual = angles.geographic_distance(0., 0.5, 0., 0.5)
self.assertAlmostEqual(actual, 0., 1)
def bounding_box(fcst, pad=0.1, lon_pad=None, lat_pad=None):
lons = np.unique(fcst['longitude'].values)
lats = np.unique(fcst['latitude'].values)
lon_diffs = angles.angle_diff(lons[:, None], lons)
lat_diffs = angles.angle_diff(lats[:, None], lats)
western_most_ind = np.nonzero(np.all(lon_diffs >= 0., axis=0))[0]
western_most = np.unique(lons[western_most_ind]).item()
eastern_most_ind = np.nonzero(np.all(lon_diffs <= 0., axis=0))[0]
eastern_most = np.unique(lons[eastern_most_ind]).item()
northern_most_ind = np.nonzero(np.all(lat_diffs <= 0., axis=0))[0]
northern_most = np.unique(lats[northern_most_ind]).item()
southern_most_ind = np.nonzero(np.all(lat_diffs >= 0., axis=0))[0]
southern_most = np.unique(lats[southern_most_ind]).item()
# count the number of lons greater than and less than each lon
# and take the difference. The longitude (or pair of lons) that
# minimize this help us determine the median. This allows different
# definitions of longitude.
lon_rel_loc = np.abs(np.sum(lon_diffs >= 0., axis=0) -
np.sum(lon_diffs <= 0., axis=0))
central_lons = lons[lon_rel_loc == np.min(lon_rel_loc)]
# make sure the central two aren't too far apart.
assert np.max(central_lons) - np.min(central_lons) < 90
median_lon = np.median(central_lons)
lat_rel_loc = np.abs(np.sum(lat_diffs >= 0., axis=0) -
np.sum(lat_diffs <= 0., axis=0))
central_lats = lats[lat_rel_loc == np.min(lat_rel_loc)]
median_lat = np.median(central_lats)
width = angles.geographic_distance(western_most, median_lat,
eastern_most, median_lat)
height = angles.geographic_distance(median_lon, northern_most,
median_lon, southern_most)
if lon_pad is None:
lon_pad = pad * np.abs(angles.angle_diff(eastern_most,
western_most))
if lat_pad is None:
lat_pad = pad * np.abs(angles.angle_diff(northern_most,
southern_most))
return {'llcrnrlon': western_most - lon_pad,
'urcrnrlon': eastern_most + lon_pad,
'urcrnrlat': northern_most + lat_pad,
'llcrnrlat': southern_most - lat_pad,
'width': width * (1. + 2 * pad),
'height': height * (1. + 2 * pad),
'lon_0': median_lon,
'lat_0': median_lat}