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    "# Orbital Mean-Element Messages\n",
    "\n",
    "Orbital Mean-Element Messages (OMMs) are standardized data products defined by CCSDS to exchange satellite orbital elements in a machine-readable way.  They are growing in popularity and are now supported at https://www.celetrak.org and https://www.space-track.org.\n",
    "\n",
    "The standard is described at: https://ccsds.org/Pubs/502x0b3e1.pdf though neigher of the web pages above appear to adhere to it rigidly.\n",
    "\n",
    "OMMs can be encoded within:\n",
    "* JSON - very common and straightforward\n",
    "* XML - A bit more confusing, as there are more levels of heirarchy\n",
    "* KVN - Key-value notation, a terrible way for representing the data as it imposes very little structure\n",
    "\n",
    "`satkit` supports SGP4 propagation of OMMs represented as python dictionaries or lists of python dictionaries\n",
    "\n",
    "`satkit` does **not** support KVN\n"
   ]
  },
  {
   "cell_type": "markdown",
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   "source": [
    "## Example 1\n",
    "\n",
    "The following example loads an OMM as json from https://www.celestrak.org , generates state vectors from the output, and converts the state vectors to geodetic positions"
   ]
  },
  {
   "cell_type": "code",
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   "source": [
    "import satkit as sk\n",
    "import json\n",
    "import requests\n",
    "\n",
    "# Query the current ephemeris for the International Space Station (ISS)\n",
    "url = 'https://celestrak.org/NORAD/elements/gp.php?CATNR=25544&FORMAT=json'\n",
    "with requests.get(url) as response:\n",
    "    omm = response.json()\n",
    "\n",
    "# Get a representative time from the output\n",
    "epoch = sk.time(omm[0]['EPOCH'])\n",
    "# crate a list of times .. once every 10 minutes\n",
    "time_array = [epoch + sk.duration(minutes=i*10) for i in range(6)]\n",
    "\n",
    "# TEME (inertial) output from SGP4\n",
    "pTEME, _vTEME = sk.sgp4(omm[0], time_array)\n",
    "\n",
    "# Rotate to Earth-fixed\n",
    "pITRF = [sk.frametransform.qteme2itrf(t) * p for t, p in zip(time_array, pTEME)]\n",
    "\n",
    "# Geodetic coordinates of space station at given times\n",
    "coord = [sk.itrfcoord(x) for x in pITRF]\n"
   ]
  },
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   "source": [
    "## Example 2\n",
    "\n",
    "Same as example above, except OMM is in XML.  Note the additional complexity in the hierarchy\n",
    "\n",
    "also, plot the ground track"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "8576cfcc",
   "metadata": {},
   "outputs": [],
   "source": [
    "import satkit as sk\n",
    "import xmltodict\n",
    "import requests\n",
    "import plotly.graph_objects as go\n",
    "import numpy as np\n",
    "\n",
    "# Query the current ephemeris for the International Space Station (ISS)\n",
    "url = 'https://celestrak.org/NORAD/elements/gp.php?CATNR=25544&FORMAT=xml'\n",
    "with requests.get(url) as response:\n",
    "    omm = xmltodict.parse(response.text)\n",
    "\n",
    "# Navigate to the relevant part of the parsed XML\n",
    "# Ugghh, what a terrible structure\n",
    "omm = omm['ndm']['omm']['body']['segment']['data']\n",
    "\n",
    "\n",
    "# Get a representative time from the output\n",
    "epoch = sk.time(omm['meanElements']['EPOCH'])\n",
    "# crate a list of times .. once every 10 minutes\n",
    "time_array = [epoch + sk.duration(minutes=i) for i in range(97)]\n",
    "\n",
    "# TEME (inertial) output from SGP4\n",
    "pTEME, _vTEME = sk.sgp4(omm, time_array)\n",
    "\n",
    "# Rotate to Earth-fixed\n",
    "pITRF = [sk.frametransform.qteme2itrf(t) * p for t, p in zip(time_array, pTEME)]\n",
    "\n",
    "coord = [sk.itrfcoord(x) for x in pITRF]\n",
    "\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='ISS 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 time_array], y=np.array(alt)/1e3, mode='lines'))\n",
    "fig.update_layout(yaxis_title='Altitude (km)', xaxis_title='Time', font=dict(size=14), title='ISS Altitude vs Time')\n",
    "fig.show()"
   ]
  }
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