def max_drift_filter(n1, x1, y1, n2, x2, y2, max_speed=0.5, max_drift=None, **kwargs):
''' Filter out too high drift (m/s)
Parameters
----------
n1 : First Nansat object
x1 : 1D vector - X coordinates of keypoints on image 1
y1 : 1D vector - Y coordinates of keypoints on image 1
n2 : Second Nansat object
x2 : 1D vector - X coordinates of keypoints on image 2
y2 : 1D vector - Y coordinates of keypoints on image 2
max_speed : float - maximum allowed ice drift speed, m/s
max_drift : float - maximum allowed drift distance, meters
Returns
-------
x1 : 1D vector - filtered source X coordinates on img1, pix
y1 : 1D vector - filtered source Y coordinates on img1, pix
x2 : 1D vector - filtered destination X coordinates on img2, pix
y2 : 1D vector - filtered destination Y coordinates on img2, pix
Note
----
If time_coverage_start is not avaialabe from input data then the <max_speed> threshold
is not used and the user should set value for <max_drift>.
'''
# chack if input datasets have time stamp
try:
n1_time_coverage_start = n1.time_coverage_start
n2_time_coverage_start = n2.time_coverage_start
except ValueError:
data_has_timestamp = False
else:
data_has_timestamp = True
if data_has_timestamp:
# if datasets have timestamp compare with speed
gpi = get_speed_ms(n1, x1, y1, n2, x2, y2) <= max_speed
elif max_drift is not None:
# if datasets don't have timestamp compare with displacement
gpi = 1000.*get_displacement_km(n1, x1, y1, n2, x2, y2) <= max_drift
else:
# if max displacement is not given - raise error
raise ValueError('''
Error while filtering matching vectors!
Input data does not have time stamp, and <max_drift> is not set.
Either use data supported by Nansat, or
provide a value for <max_drift> - maximum allowed ice displacement between images (meters).
Examples:
uft, vft, lon1ft, lat1ft, lon2ft, lat2ft = sid.get_drift_FT(max_drift=10000)
x1, y1, x2, y2 = feature_tracking(n1, n2, max_drift=10000)
Vectors with displacement higher than <max_drift> will be removed.
''')
print('MaxDrift filter: %d -> %d' % (len(x1), len(gpi[gpi])))
return x1[gpi], y1[gpi], x2[gpi], y2[gpi]
def test_get_displacement_km(self):
''' Shall find matching coordinates and plot quiver in lon/lat'''
keyPoints1, descr1 = find_key_points(self.img1, nFeatures=self.nFeatures)
keyPoints2, descr2 = find_key_points(self.img2, nFeatures=self.nFeatures)
x1, y1, x2, y2 = get_match_coords(keyPoints1, descr1,
keyPoints2, descr2)
h = get_displacement_km(self.n1, x1, y1, self.n2, x2, y2)
plt.scatter(x1, y1, 30, h)
plt.colorbar()
plt.savefig('sea_ice_drift_tests_%s.png' % inspect.currentframe().f_code.co_name)
plt.close('all')
self.assertTrue(len(h) == len(x1))