Satellite

The GDK layer "Satellite" defined in the namespace TPG.GeoFramework.SatelliteLayer handles satellites, they can therefore easily be separated from other draw types. Satellite objects in this layer are controlled using the TPG.GeoFramework.SatelliteLayer.SatelliteLayerViewModel class.

What is a satellite?

A satellite consists of two draw objects; a satellite position object of type symbol and a satellite trajectory object of type line. Both object types are not required, but are usually used.

ISatellitePosition

The satellite position is handled by the ISatellitePosition class.

ISatelliteTrajectory

The satellite trajectory is handled by the ISatelliteTrajectory class.

The TLE string

A satellite position and its trajectory is computed from a TLE string. The format of the TLE is described in https://www.space-track.org/documentation#/tle.

//Example of TLE text used in tests
public static string TestTle()
{
    var tle = "0 ISS (ZARYA)";
    tle += "\n1 25544U 98067A   20227.03014521  .00002523  00000-0  53627-4 0  9998";
    tle += "\n2 25544  51.6461  62.1977 0001435  30.4470 104.2862 15.49164713240985";
    return tle;
}

How to create satellite objects

The satellite objects are first created and then added to the satellite layer.

This test code creates a satellite position object:

var satellite = new TPG.GeoFramework.SatelliteLayer.Satellite
{
   Tle = TestTle(),
   MetadataSetting = (long)SatelliteObject.TleMetadata.All,
   RecalculateTrajectoryAlways = FullCurveCalculations
};
Assert.NotNull(satellite);

//calculate the satellite position for this time
var time = new DateTime(2020, 08, 14, 7, 55, 26, DateTimeKind.Utc);
Assert.IsTrue(satellite.CreateSatellite(time));
Assert.AreEqual(1, satellite.Objects.Count);
Assert.IsNotNull(satellite.Objects.First() as ISatellitePosition);

This code shows how to add satellites to the satellite layer:

//The satellite layer
SatelliteLayerViewModel _satelliteLayerViewModel = ...

//create satellites, details not shown
var createdSatellites = new List<ISatellite>();
createdSatellites = CreateSatellites();

//prevent refresh while we are adding satellites
_satelliteLayerViewModel.LockRedraw = true;

foreach (var satellite in createdSatellites)         
   _satelliteLayerViewModel.AddSatellite(satellite);

//will refresh rendering
_satelliteLayerViewModel.LockRedraw = false;