Merge pull request #121 from Spect4tor/main

fixed geoloc_example and added variable descriptions

pyorbital/geoloc_example.py

@@ -29,34 +29,42 @@
 from mpl_toolkits.basemap import Basemap
 import matplotlib.pyplot as plt
 
+# Couple of example Two Line Elements
 tle1 = "1 33591U 09005A   12345.45213434  .00000391  00000-0  24004-3 0  6113"
 tle2 = "2 33591 098.8821 283.2036 0013384 242.4835 117.4960 14.11432063197875"
 
+# Choosing a specific time, this should be relatively close to the issue date of the TLE
 t = datetime(2012, 12, 12, 4, 16, 1, 575000)
-
-scanline_nb = 351
-
+# this is the number of full scan rotations
+scans_nb = 10
 # we take only every 40th point for plotting clarity
 scan_points = np.arange(24, 2048, 40)
-
+# This the maximum scan angle away from nadir for the given TLE that still sees earth.
+scan_angle = 55.37
+# period of one full rotation 1/6 s
+scan_p = 0.16666667
+# integration time of instrument
+int_t = 0.000025
 
 # build the avhrr instrument (scan angles)
-avhrr = np.vstack(((scan_points - 1023.5) / 1024 * np.deg2rad(-55.37),
-                   np.zeros((len(scan_points),)))).transpose()
-avhrr = np.tile(avhrr, [scanline_nb, 1])
+# creates list of radian angles centered around nadir based on the scan points that see earth
+avhrr = np.vstack(((scan_points / 1023.5-1) * np.deg2rad(-scan_angle),
+                   np.zeros((len(scan_points),))))
+avhrr = np.tile(
+        avhrr[:, np.newaxis, :], [1, scans_nb, 1])
 
 # building the corresponding times array
-offset = np.arange(scanline_nb) * 0.1666667
-times = (np.tile(scan_points * 0.000025 + 0.0025415, [scanline_nb, 1])
-         + np.expand_dims(offset, 1))
+times = np.tile(scan_points * int_t, [scans_nb, 1])
+offset = np.arange(scans_nb) * scan_p
+times += np.expand_dims(offset, 1)
 
 # build the scan geometry object
-sgeom = ScanGeometry(avhrr, times.ravel())
+sgeom = ScanGeometry(avhrr, times)
 
-# roll, pitch, yaw in radians
+# roll, pitch, yaw in radians. This is a static offset.
 rpy = (0, 0, 0)
 
-# print the lonlats for the pixel positions
+# print the longitude and latitude for the pixel positions
 s_times = sgeom.times(t)
 pixels_pos = compute_pixels((tle1, tle2), sgeom, s_times, rpy)
 pos_time = get_lonlatalt(pixels_pos, s_times)