Add waypoint generator

utils/tle/import-tle.sh

@@ -0,0 +1,30 @@
+#!/bin/sh
+
+set -u
+set -e
+
+search=$1
+
+# Get the ids of sats matching the search term
+if [ ! -f ids.txt ]
+then
+	curl https://celestrak.com/pub/satcat.txt | grep "$search" | cut -b14-18 > ids.txt
+fi
+
+# Download TLE data for each sat
+while read id
+do
+	if [ ! -f $id.txt ]
+	then
+		wget "https://celestrak.com/satcat/tle.php?CATNR=$id" -O $id.txt
+	fi
+	# 6000 s ~ 95 min ~ 1 orbital period
+done < ids.txt
+
+while read id
+do
+	if [ ! -f $id.waypoints ]
+	then
+		./tle2wps.py $id.txt 2020 08 28 6000 > $id.waypoints
+	fi
+done < ids.txt

utils/tle/tle2wps.py

@@ -0,0 +1,61 @@
+#!/usr/bin/env python3
+
+"""
+Creates a stream of waypoints using SGP4 and two-line element (TLE) information
+
+Up-to-date TLEs can be obtained from [Celestrak](https://celestrak.com/satcat/search.php)
+"""
+
+import logging as log
+import argparse
+
+from datetime import datetime
+from skyfield.api import EarthSatellite, Time, load, utc
+
+log.basicConfig(level=log.DEBUG)
+
+"""
+Class for exporting `ns3::Waypoint` in its own serialized format.
+
+See `ns3::Waypoint::operator <<`
+"""
+class Waypoint:
+    def __init__(self, time, x, y, z):
+        self.time = time
+        self.x = x
+        self.y = y
+        self.z = z
+
+    def __repr__(self):
+        return("%fs $ %f:%f:%f" % (self.time, self.x, self.y, self.z))
+
+
+"""
+Use Skyfield to generate the waypoints
+"""
+if __name__ == "__main__":
+    parser = argparse.ArgumentParser(description='Process some integers.')
+    parser.add_argument('tle', type=str, help='Two-line element data')
+    parser.add_argument('year', type=int, help='year to start at')
+    parser.add_argument('month', type=int, help='month to start at')
+    parser.add_argument('day', type=int, help='day to start at')
+    parser.add_argument('duration', type=int, help='duration in seconds')
+    args = parser.parse_args()
+
+    ts = load.timescale(builtin=True)
+    sats = load.tle_file(args.tle)
+    log.info("Loaded %d satellites" % len(sats))
+
+    duration = args.duration
+
+    for sat in sats:
+        log.info("Generating waypoints for %s" % sat.name)
+        # skyfield will automatically overflow the seconds and produce the next correct second
+        t_start = ts.utc(year=args.year, month=args.month, day=args.day)
+        for t in ts.utc(year=args.year, month=args.month, day=args.day, second=range(1, duration, 1)):
+            geocentric = sat.at(t)
+            t_rel = (t.tai - t_start.tai) * 10**5
+            d = geocentric.itrf_xyz().m
+            wp = Waypoint(t_rel, d[0], d[1], d[2])
+            print(wp)
+