/// <summary>
/// Performs latitude calculations as part of lat/long to scanning angle. These are cached in order to avoid
/// repeating latitude calculations for every pixel.
/// </summary>
private LatitudeCalculations CalculateGeostationaryLatitude(int y)
{
var target = _target;
var yOffset = _yOffset;
return(LatitudeCalculationCache.GetOrAdd(y, angle =>
{
// Convert pixel row to latitude
var projectionY = ProjectionAngleConverter.FromY(y, target.Height + yOffset * 2);
// Perform and cache intermediary geostationary latitude calculations
return GeostationaryProjection.LatitudeCalculations(projectionY);
}));
}
public void Invoke(int y)
{
var span = _target.GetPixelRowSpan(y);
// Calculate or retrieve the latitude calculation component of geostationary projection
var latitudeCalculations = CalculateGeostationaryLatitude(y + _yOffset);
// Convert image x,y to Mercator projection angle
var targetWidth = _registration.Width * 2;
var projectionY = ProjectionAngleConverter.FromY(y + _yOffset, _registration.Height);
for (var x = 0; x < span.Length; x++)
{
var projectionX = ProjectionAngleConverter.FromX(x + _xOffset, targetWidth);
// Convert latitude/longitude to geostationary scanning angle
GeostationaryProjection.ToScanningAngle(latitudeCalculations, projectionX, _registration.Definition, out var scanningX, out var scanningY);
// Map pixel from satellite image back to target image
span[x] = GetTargetColour(scanningX, scanningY, projectionY, projectionX);
}
}
public void FromY()
{
Angle.FromRadians(ProjectionAngleConverter.FromY(0, 200)).Degrees.Should().BeApproximately(90, Precision);
Angle.FromRadians(ProjectionAngleConverter.FromY(200, 200)).Degrees.Should().BeApproximately(-90, Precision);
Angle.FromRadians(ProjectionAngleConverter.FromY(100, 200)).Degrees.Should().BeApproximately(0, Precision);
}