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fixed geoloc_example and added variable descriptions #121

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Mar 22, 2023
Merged

fixed geoloc_example and added variable descriptions #121

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12dd464
fixed geoloc_example and added variable descriptions
Spect4tor Mar 8, 2023
83c1689
Removed type specification of scan_nb
Spect4tor Mar 22, 2023
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34 changes: 21 additions & 13 deletions pyorbital/geoloc_example.py
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Original file line number Diff line number Diff line change
Expand Up @@ -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)
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