/// <summary>
/// Get the terrain elevation map corresponding to the specified position.
/// </summary>
/// <param name="viewPosition">
/// The <see cref="Vertex2d"/> that specify the current view position, using an absolute cartesian reference system.
/// </param>
/// <returns>
/// It returns the <see cref="Image"/> that contains the terrain elevation data corresponding to <paramref name="viewPosition"/>.
/// </returns>
public Image GetTerrainElevationMap(Vertex2d viewPosition)
{
// Apply clipmap offset
double lodUnitScale = Math.Pow(2.0, Lod) * UnitScale;
Vertex2d texturePositionOffset = viewPosition - _CurrentViewPosition;
texturePositionOffset /= lodUnitScale;
// Determine whether an texture update is not required
bool xNormOffset = texturePositionOffset.x > -1.0 && texturePositionOffset.x < 1.0;
bool yNormOffset = texturePositionOffset.y > -1.0 && texturePositionOffset.y < 1.0;
if (xNormOffset && yNormOffset && _TerrainElevationInitialized)
{
return(null);
}
// Discard fractional part, move towards zero
texturePositionOffset = new Vertex2d(Math.Truncate(texturePositionOffset.x), Math.Truncate(texturePositionOffset.y));
// Determine the dataset section to load
Vertex2d rasterPosition = _CurrentTexPosition + (texturePositionOffset * Math.Pow(2.0, Lod));
double w2 = _TerrainElevation.Width / 2, h2 = _TerrainElevation.Height / 2;
// Specify the LOD 0 size
// Note: the dataset should have overviews, in order to make CPU friendly update
w2 *= Math.Pow(2.0, Lod);
h2 *= Math.Pow(2.0, Lod);
double x1 = rasterPosition.x - w2, x2 = rasterPosition.x + w2;
double y1 = rasterPosition.y - h2, y2 = rasterPosition.y + h2;
Rectangle datasetSection = new Rectangle();
datasetSection.X = (int)Math.Floor(x1);
datasetSection.Y = (int)Math.Floor(y1);
datasetSection.Width = (int)Math.Floor(x2 - x1);
Debug.Assert(datasetSection.Width % _TerrainElevation.Width == 0);
datasetSection.Height = (int)Math.Floor(y2 - y1);
Debug.Assert(datasetSection.Height % _TerrainElevation.Height == 0);
// Update current terrain elevation, following the updated position
ImageCodecCriteria datasetCriteria = new ImageCodecCriteria();
datasetCriteria.ImageSection = datasetSection;
GdalImageCodecPlugin.Load_GrayIndex(_DatabaseDataset, 1, datasetCriteria, _TerrainElevation);
// Update current positions
_CurrentTexPosition = rasterPosition;
_CurrentViewPosition = _CurrentViewPosition + (texturePositionOffset * lodUnitScale);;
// Trace.TraceInformation("Texture LOD {0} reposition: {1}", Lod, _CurrentTexPosition);
// Allow first time initialization
_TerrainElevationInitialized = true;
return(_TerrainElevation);
}
/// <summary>
/// Static constructor.
/// </summary>
static Terrain()
{
GdalImageCodecPlugin.AllRegister();
}
