Add ground_track.py

examples/iss.txt

@@ -0,0 +1,3 @@
+ISS (ZARYA)
+1 25544U 98067A   19004.59354167  .00000715  00000-0  18267-4 0  9995
+2 25544  51.6416  95.0104 0002419 236.2184 323.8248 15.53730729149833

examples/sathyabamasat.txt

@@ -0,0 +1,3 @@
+SATHYABAMASAT
+1 41600U 16040B   19310.17193730  .00001455  00000-0  63216-4 0  9994
+2 41600  97.3537  10.1403 0012192 255.4467 104.5418 15.23822105187350

python/README.md

@@ -0,0 +1,18 @@
+## Notes
+
+
+## Setup
+- Dependency installation via pip:
+  ```
+  pip install -r requirements.txt
+  ```
+
+- In order to be able to use `ground_track.py`,
+  download [earth.png](https://raw.githubusercontent.com/galactics/beyond/master/doc/source/_static/earth.png) into this directory.
+
+## Usage
+
+- Plot the ground track of satellite based on it's TLE around the epoch:
+  ```
+  ./ground_track.py ../examples/sathyabamasat.txt
+  ```

python/ground_track.py

@@ -0,0 +1,121 @@
+#!/usr/bin/env python3
+
+"""
+Script showing the position of the ISS at the time of the TLE
+and the ground track for the previous and the next orbit
+
+(original) source: https://github.com/galactics/beyond/blob/master/doc/source/_static/ground-track.py
+"""
+
+import sys
+import argparse
+
+import numpy as np
+import matplotlib.pyplot as plt
+
+from pathlib import Path
+
+from beyond.io.tle import Tle
+from beyond.dates import Date, timedelta
+
+
+def tle_from_file(filename):
+    '''
+    Returns: TLE:Tle, Object name:str
+    '''
+
+    with open(filename, 'r') as f:
+        lines = f.readlines()
+
+    return Tle(''.join(lines)), lines[0].strip()
+
+
+if __name__ == "__main__":
+    # Parse arguments
+    parser = argparse.ArgumentParser(
+        description="Plot the ground track of a TLE")
+    parser.add_argument('TLEFILE', help="the tle file", type=str)
+
+    args = parser.parse_args()
+
+    # Parsing of TLE
+    tle, name = tle_from_file(args.TLEFILE)
+   
+    # Conversion into `Orbit` object
+    orb = tle.orbit()
+    
+    # Tables containing the positions of the ground track
+    latitudes, longitudes = [], []
+    prev_lon, prev_lat = None, None
+    
+    period = orb.infos.period
+    start = orb.date - period
+    stop = 2 * period
+    step = period / 100
+    
+    for point in orb.ephemeris(start=start, stop=stop, step=step):
+    
+        # Conversion to earth rotating frame
+        point.frame = 'ITRF'
+    
+        # Conversion from cartesian to spherical coordinates (range, latitude, longitude)
+        point.form = 'spherical'
+    
+        # Conversion from radians to degrees
+        lon, lat = np.degrees(point[1:3])
+    
+        # Creation of multiple segments in order to not have a ground track
+        # doing impossible paths
+        if prev_lon is None:
+            lons = []
+            lats = []
+            longitudes.append(lons)
+            latitudes.append(lats)
+        elif orb.i < np.pi /2 and (np.sign(prev_lon) == 1 and np.sign(lon) == -1):
+            lons.append(lon + 360)
+            lats.append(lat)
+            lons = [prev_lon - 360]
+            lats = [prev_lat]
+            longitudes.append(lons)
+            latitudes.append(lats)
+        elif orb.i > np.pi/2 and (np.sign(prev_lon) == -1 and np.sign(lon) == 1):
+            lons.append(lon - 360)
+            lats.append(lat)
+            lons = [prev_lon + 360]
+            lats = [prev_lat]
+            longitudes.append(lons)
+            latitudes.append(lats)
+    
+        lons.append(lon)
+        lats.append(lat)
+        prev_lon = lon
+        prev_lat = lat
+    
+
+    fig = plt.figure(figsize=(15.2, 8.2))
+    ax = fig.add_subplot(111)
+
+    ax.set_title(name)
+
+    # Plot earth
+    img = Path(__file__).parent / "earth.png"
+    im = plt.imread(str(img))
+    ax.imshow(im, extent=[-180, 180, -90, 90])
+
+    # Plot ground track 
+    for lons, lats in zip(longitudes, latitudes):
+        ax.plot(lons, lats, 'r-')
+
+    # Plot location at epoch time 
+    lon, lat = np.degrees(orb.copy(frame='ITRF', form='spherical')[1:3])
+    ax.plot([lon], [lat], 'bo')
+
+    ax.set_xlim([-180, 180])
+    ax.set_ylim([-90, 90])
+    ax.grid(True, color='w', linestyle=":", alpha=0.4)
+    ax.set_xticks(range(-180, 181, 30))
+    ax.set_yticks(range(-90, 91, 30))
+    fig.tight_layout()
+    
+    if "no-display" not in sys.argv:
+        plt.show()