Below are examples illustrating a few common use-cases.
JSON is a great format for configuring applications and for exchanging data over the internet:
Assuming an input.json file as follows:
{
"Key 1": "Hello World!"
}the following code:
// Setup JSON file
File jsonFile = File::Path(Path::String("/path/to/input.json")) ;
// Create object by loading JSON file
Object object = Object::Load(jsonFile) ;
// Get object value
String value = object["Key 1"].getString() ; // "Hello World!"
// Set object value
object["Key 2"] = Object::Integer(123) ;
// Save object
object.writeToFile(File::Path(Path::String("/path/to/output.json"))) ;will return an output.json file as:
{
"Key 1": "Hello World!",
"Key 2": 123
}Instead of using real numbers, units can be used to store physical values.
This makes code more explicit, facilitates conversions and may avoid potential errors.
// Length
Length distance = Length::Meters(3.5) ;
distance.getIn(Length::Unit::Meter) ;
distance.getIn(Length::Unit::Foot) ;
distance.getIn(Length::Unit::TerrestrialMile) ;
distance.getIn(Length::Unit::NauticalMile) ;
distance.getIn(Length::Unit::AstronomicalUnit) ;
// Angle
Angle angle = Angle::Degrees(35.6) ;
angle.getIn(Angle::Unit::Degree) ;
angle.getIn(Angle::Unit::Radian) ;
angle.getIn(Angle::Unit::ArcMinute) ;
angle.getIn(Angle::Unit::ArcSecond) ;
// Also available for Mass, Time, Volume, Density, ...// Setup environment model
Environment environment = Environment::Default() ; // Using the default configuration, to simplify things
// Set environment time
environment.setInstant(Instant::DateTime(DateTime::Parse("2018-01-01T00:00:00Z"))) ;
// Access Solar System's objects
Object earth = environment.accessObject(Object::Type::Earth) ;
Object sun = environment.accessObject(Object::Type::Sun) ;
Object moon = environment.accessObject(Object::Type::Moon) ;
// Get object properties
Length earthEquatorialRadius = earth.getEquatorialRadius() ;
Mass earthMass = earth.getMass() ;
Position earthPosition_ECI = earth.getFixedFrame().getPositionIn(Frame::ECI) ;
Quaternion earthOrientation_ECI = earth.getFixedFrame().getOrientationIn(Frame::ECI) ;
Position sunPosition_ECI = sun.getFixedFrame().getPositionIn(Frame::ECI) ;
Position moonPosition_ECI = moon.getFixedFrame().getPositionIn(Frame::ECI) ;
// Setup a satellite position
Position satellitePosition_ECI = {7000e3, 0.0, 0.0} ;
// Calculate derived quantities
Vector3d satelliteToSunDirection_ECI = (sunPosition_ECI - satellitePosition_ECI).normalized() ;
// Check if the satellite is in eclipse
// (this is a simplified version, a more elaborated one would use a cone instead of a ray)
Ray satelliteToSunRay(satellitePosition_ECI, satelliteToSunDirection_ECI) ; // Ray starting from the satellite, to the Sun
bool isSatelliteInEclipse = environment.isRayIntersectingAnyObject(satelliteToSunRay, { sun }) ; // Any object, except the Sun itself// Setup TLE file
File tleFile = File::Path(Path::String("/path/to/satellite.tle")) ;
// Load TLE
TLE tle = TLE::Load(tleFile) ;
// Generate orbit using SGP4
Instant startTime = Instant::DateTime(DateTime::Parse("2018-01-01T00:00:00Z")) ;
Instant endTime = startTime + Duration::Hours(10.0) ;
Duration stepDuration = Duration::Seconds(5.0) ;
Array<Instant> timeGrid = Interval(startTime, endTime).generateGrid(stepDuration) ;
Orbit satelliteOrbit = Orbit::SGP4(timeGrid, SGP4::TLE(tle)) ;
// Print orbit states
for (const auto& state : satelliteOrbit)
{
std::cout << state.getTime().getString() << " - " << state.getPositionIn(Frame::ECI).getString() << std::endl ;
}
// Dump orbit data to file
orbit.writeToFile(File::Path(Path::String("/path/to/orbit.csv"))) ;
// Generate access
Position groundStationPosition = Position::LLA(30.0, 50.0, 145.0) ;
Array<Access> accessArray = Access::Generate(groundStationPosition, satelliteOrbit) ;
// Print access
for (const auto& access : accessArray)
{
std::cout << access << std::endl ;
}// Generate orbit using SGP4
Orbit satelliteOrbit = ... ; // From previous example
// Filter predicate
auto stateFilter = [] (const State& aState) -> bool
{
return aState.getPositionIn(Frame::ECEF).z() >= 0.0 ; // Only over Northern hemisphere
} ;
// Iterate over states matching the filter
for (const auto& state : satelliteOrbit.getFilteredStates(stateFilter))
{
// Do something...
}// Setup an environment model
Environment environment = Environment::Default() ; // Using the default configuration, to simplify things
// Set the environment time
environment.setInstant(Instant::DateTime(DateTime::Parse("2018-01-01T00:00:00Z"))) ;
// Setup a pyramidal sensor model (in Earth-Centered, Earth-Fixed [ECEF] frame)
Position sensorPosition_ECEF = {7000e3, 0.0, 0.0} ; // Sensor is located at equator
Vector3d sensorDirection_ECEF = {-1.0, 0.0, 0.0} ; // Sensor is nadir pointing
Vector3d sensorPlaneXAxis_ECEF = {0.0, 0.0, 1.0} ;
Vector3d sensorPlaneYAxis_ECEF = {0.0, 1.0, 0.0} ;
Angle sensorFieldOfViewHalfAngle = Angle::Degrees(10.0) ;
Pyramid sensorModel_ECEF( sensorPosition_ECEF,
sensorDirection_ECEF,
sensorPlaneXAxis_ECEF,
sensorPlaneYAxis_ECEF,
sensorFieldOfViewHalfAngle) ;
// Calculate sensor intersection with Earth
Object earth = environment.accessObject(Object::Type::Earth) ;
Ellipsoid earthEllipsoid_ECEF = earth.getEllipsoidInFrame(Frame::ECEF) ;
Intersection sensorIntersectionWithEarth_ECEF = earthEllipsoid_ECEF.getIntersectionWith(sensorModel_ECEF) ;
if (sensorIntersectionWithEarth_ECEF.isDefined()) // If sensor field of view is intersecting Earth
{
// Convert intersection into area
Area sensorIntersectionArea = Area::Empty() ;
for (const auto& intersectionPoint_ECEF : sensorIntersectionWithEarth_ECEF.getPoints())
{
Position intersectionPosition = Position::ECEF(intersectionPoint_ECEF) ;
Angle intersectionLatitude = intersectionPosition.getLatitude() ;
Angle intersectionLongitude = intersectionPosition.getLongitude() ;
sensorIntersectionArea.add(intersectionPosition) ;
}
// Print out intersection area in EWKT format
std::cout << sensorIntersectionArea.getString(Format::EWKT) << std::endl ;
}