public void GetNearestElevationPostColumnAndRowForNorthEastCoordinates(float feetNorth, float feetEast, uint lod, out int col, out int row)
{
var feetBetweenElevationPosts = _distanceBetweenElevationPostsCalculator.GetNumFeetBetweenElevationPosts(lod);
col = (int)Math.Floor(feetEast / feetBetweenElevationPosts);
row = (int)Math.Floor(feetNorth / feetBetweenElevationPosts);
_elevationPostCoordinateClamper.ClampElevationPostCoordinates(ref row, ref col, lod);
}
public float CalculateTerrainHeight(float feetNorth, float feetEast, uint lod)
{
int col;
int row;
var feetAcross = _distanceBetweenElevationPostsCalculator.GetNumFeetBetweenElevationPosts(lod);
//determine the column and row in the DTED matrix where the nearest elevation post can be found
_nearestElevationPostColumnAndRowCalculator.GetNearestElevationPostColumnAndRowForNorthEastCoordinates(feetNorth, feetEast, lod, out col, out row);
//retrieve the 4 elevation posts which form a box around our current position (origin point x=0,y=0 is in lower left)
var Q11 = _columnAndRowElevationPostRecordRetriever.GetElevationPostRecordByColumnAndRow(col, row, lod);
var Q21 = _columnAndRowElevationPostRecordRetriever.GetElevationPostRecordByColumnAndRow(col + 1, row, lod);
var Q22 = _columnAndRowElevationPostRecordRetriever.GetElevationPostRecordByColumnAndRow(col + 1, row + 1, lod);
var Q12 = _columnAndRowElevationPostRecordRetriever.GetElevationPostRecordByColumnAndRow(col, row + 1, lod);
if (Q11 == null || Q21 == null || Q22 == null || Q12 == null)
{
return(0);
}
//determine the North/East coordinates of these 4 posts, respectively
var Q11North = row * feetAcross;
var Q11East = col * feetAcross;
float FQ11 = Q11.Elevation;
var Q21East = (col + 1) * feetAcross;
float FQ21 = Q21.Elevation;
float FQ22 = Q22.Elevation;
var Q12North = (row + 1) * feetAcross;
float FQ12 = Q12.Elevation;
//perform bilinear interpolation on the 4 outer elevation posts relative to our actual center post
//see: http://en.wikipedia.org/wiki/Bilinear_interpolation
var x = feetEast;
var y = feetNorth;
var x1 = Q11East;
var x2 = Q21East;
var y1 = Q11North;
var y2 = Q12North;
var result =
(
((FQ11 / ((x2 - x1) * (y2 - y1))) * (x2 - x) * (y2 - y))
+
((FQ21 / ((x2 - x1) * (y2 - y1))) * (x - x1) * (y2 - y))
+
((FQ12 / ((x2 - x1) * (y2 - y1))) * (x2 - x) * (y - y1))
+
((FQ22 / ((x2 - x1) * (y2 - y1))) * (x - x1) * (y - y1))
);
return(result);
}
public float GetDistanceInFeetBetweenElevationPosts(uint lod)
{
return(_distanceBetweenElevationPostsCalculator.GetNumFeetBetweenElevationPosts(lod));
}