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   "source": [
    "# Two-Line Element Set\n",
    "\n",
    "Examples showing how to use two-line element sets to generate a state vector and get geodetic position of satellite"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Generate State Vector"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "import satkit as sk\n",
    "\n",
    "# The two-line element set\n",
    "# Lets pick a random StarLink satellite\n",
    "# The lines below were downloaded from https://www.celetrack.org\n",
    "tle_lines = [\n",
    "    '0 STARLINK-30477',\n",
    "    '1 57912U 23146X   24099.49439401  .00006757  00000+0  51475-3 0  9997',\n",
    "    '2 57912  43.0018 157.5807 0001420 272.5369  87.5310 15.02537576 31746'\n",
    "]\n",
    "\n",
    "# Create a TLE object\n",
    "starlink30477 = sk.TLE.from_lines(tle_lines)\n",
    "\n",
    "# We want the orbital state at April 9 2024, 12:00pm UTC\n",
    "thetime = sk.time(2024, 4, 9, 12, 0, 0)\n",
    "\n",
    "# The state is output in the \"TEME\" frame, which is an approximate inertial\n",
    "# frame that does not include precession or nutation\n",
    "# pTEME is geocentric position in meters\n",
    "# vTEME is geocentric velocity in meters / second\n",
    "# for now we will ignore the velocity\n",
    "pTEME, _vTEME = sk.sgp4(starlink30477, thetime)\n",
    "\n",
    "# Suppose we want currrent latitude, longitude, and altitude of satellite:\n",
    "# we need to rotate into an Earth-fixed frame, the ITRF\n",
    "# We use a \"quaternion\" to represent the rotation.  Quaternion rotations\n",
    "# in the satkit toolbox can be represented as multiplications of a 3-vector\n",
    "pITRF = sk.frametransform.qteme2itrf(thetime) * pTEME\n",
    "\n",
    "# Now lets make a \"ITRFCoord\" object to extract geodetic coordinates\n",
    "coord = sk.itrfcoord(pITRF)\n",
    "\n",
    "# Get the latitude, longitude, and \n",
    "# altitude (height above ellipsoid, or hae) of the satellite\n",
    "print(coord)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Plot satellite ground track"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "import satkit as sk\n",
    "import numpy as np\n",
    "import plotly.graph_objects as go\n",
    "\n",
    "# The two-line element set\n",
    "# Same satellite as above...\n",
    "# The lines below were downloaded from https://www.celetrack.org\n",
    "tle_lines = [\n",
    "    '0 STARLINK-30477',\n",
    "    '1 57912U 23146X   24099.49439401  .00006757  00000+0  51475-3 0  9997',\n",
    "    '2 57912  43.0018 157.5807 0001420 272.5369  87.5310 15.02537576 31746'\n",
    "]\n",
    "\n",
    "# Create a TLE object\n",
    "starlink30477 = sk.TLE.from_lines(tle_lines)\n",
    "\n",
    "# We want the orbital state at April 9 2024, 12:00pm UTC\n",
    "thetime = sk.time(2024, 4, 9, 12, 0, 0)\n",
    "\n",
    "# plot for 5 orbits.  The mean motion in the TLE is number of orbits in a day\n",
    "timearr = np.array([thetime + sk.duration(days=x) for x in np.linspace(0, 5/starlink30477.mean_motion, 1000)])\n",
    "\n",
    "# Get position in the TEME frame\n",
    "pTEME, _vTEME = sk.sgp4(starlink30477, timearr)\n",
    "qarr = sk.frametransform.qteme2itrf(timearr)\n",
    "pITRF = np.array([q * p for q, p in zip(qarr, pTEME)])\n",
    "coord = [sk.itrfcoord(p) for p in pITRF]\n",
    "lat, lon, alt = zip(*[(c.latitude_deg, c.longitude_deg, c.altitude) for c in coord])\n",
    "\n",
    "fig = go.Figure()\n",
    "fig.add_trace(go.Scattergeo(lat=lat, lon=lon, mode='lines'))\n",
    "fig.update_layout(margin={\"r\":0,\"t\":40,\"l\":0,\"b\":0}, title='Ground Track', geo=dict(showland=True, showcountries=True))\n",
    "fig.show()\n",
    "fig = go.Figure()\n",
    "fig.add_trace(go.Scatter(x=[t.datetime() for t in timearr], y=np.array(alt)/1e3, mode='lines'))\n",
    "fig.update_layout(yaxis_title='Altitude (km)', xaxis_title='Time', font=dict(size=14), title='Altitude vs Time')\n",
    "fig.show()"
   ]
  }
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