/// <summary>
///
/// </summary>
/// <param name="t"></param>
/// <param name="ct"></param>
/// <returns></returns>
private static PhiLam NadInterpolate(PhiLam t, NadTable ct)
{
PhiLam result, remainder;
// find indices and normalize by the cell size (so fractions range from 0 to 1)
int iPhi = (int) Math.Floor(t.Lambda /= ct.CellSize.Lambda);
int iLam = (int) Math.Floor(t.Lambda /= ct.CellSize.Phi);
// use the index to determine the remainder
remainder.Phi = t.Phi - iPhi;
remainder.Lambda = t.Lambda - iLam;
int offLam = 0; // normally we look to the right and bottom neighbor cells
int offPhi = 0;
if(remainder.Phi < .5) offLam = -1; // look to cells above current cell
if(remainder.Lambda < .5) offPhi = -1; // look to cells to the left of current cell
PhiLam topLeft = GetValue(iPhi + offPhi, iLam + offLam, ct);
PhiLam topRight = GetValue(iPhi + offPhi, iLam + offLam + 1, ct);
PhiLam bottomLeft = GetValue(iPhi + offPhi + 1, iLam + offLam, ct);
PhiLam bottomRight = GetValue(iPhi + offPhi + 1, iLam + offLam + 1, ct);
// because the fractional weights are between cells, we need to adjust the
// "remainder" so that it is now relative to the center of the top left
// cell, taking into account that the definition of the top left cell
// depends on whether the original remainder was larger than .5
remainder.Phi = (remainder.Phi > .5) ? remainder.Phi - .5 : remainder.Phi + .5;
remainder.Lambda = (remainder.Lambda > .5) ? remainder.Lambda - .5 : remainder.Phi + .5;
// The cell weight is equivalent to the area of a cell sized square centered
// on the actual point that overlaps with the cell.
// Since the overlap must add up to 1, any portion that does not overlap
// on the left must overlap on the right, hence (1-remainder.Lambda)
double mTL = remainder.Lambda*remainder.Phi;
double mTR = (1 - remainder.Lambda)*remainder.Phi;
double mBL = remainder.Lambda*(1 - remainder.Phi);
double mBR = (1 - remainder.Lambda) * (1 - remainder.Phi);
result.Lambda = mTL*topLeft.Lambda + mTR*topRight.Lambda + mBL*bottomLeft.Lambda + mBR*bottomRight.Lambda;
result.Phi = mTL*topLeft.Phi + mTR*topRight.Phi + mBL*bottomLeft.Phi + mBR*bottomRight.Phi;
return result;
}
/// <summary>
/// So that we can read from an embedded stream, this reads a NadTable
/// from any stream, not just a filename.
/// </summary>
/// <param name="str">The stream to read</param>
public void ReadStream(Stream str)
{
StreamReader sr = new StreamReader(str);
_name = sr.ReadLine();
string numText = sr.ReadToEnd();
char[] separators = new[] {' ', ',',':', (char)10};
string[] values = numText.Split(separators, StringSplitOptions.RemoveEmptyEntries);
_numLambdas = int.Parse(values[0]);
_numPhis = int.Parse(values[1]);
_lowerLeft.Lambda = double.Parse(values[3]) * DegToRad;
_lowerLeft.Phi = double.Parse(values[4]) * DegToRad;
_cellSize.Lambda = double.Parse(values[5]) * DegToRad;
_cellSize.Phi = double.Parse(values[6]) * DegToRad;
int p = 7;
_cvs = new PhiLam[_numPhis][];
for(int i = 0; i < _numPhis; i++)
{
_cvs[i] = new PhiLam[_numLambdas];
int iCheck = int.Parse(values[p]);
if (iCheck != i)
{
throw new ProjectionException(ProjectionMessages.IndexMismatch);
}
p++;
double lam = long.Parse(values[p]) * USecToRad;
_cvs[i][0].Lambda = lam;
p++;
double phi = long.Parse(values[p]) * USecToRad;
_cvs[i][0].Phi = phi;
p++;
for (int j = 1; j < _numLambdas; j++ )
{
lam += long.Parse(values[p]) * USecToRad;
_cvs[i][j].Lambda = lam;
p++;
phi += long.Parse(values[p])*USecToRad;
_cvs[i][j].Phi = phi;
p++;
}
}
}
private static PhiLam Convert(PhiLam input, bool inverse, NadTable table )
{
if (input.Lambda == HUGE_VAL) return input;
// Normalize input to ll origin
PhiLam tb = input;
tb.Lambda -= table.LowerLeft.Lambda;
tb.Phi -= table.LowerLeft.Phi;
tb.Lambda = Proj.Adjlon(tb.Lambda - Math.PI) + Math.PI;
PhiLam t = NadInterpolate(tb, table);
if(inverse)
{
PhiLam del, dif;
int i = MAX_TRY;
if (t.Lambda == HUGE_VAL) return t;
t.Lambda = tb.Lambda + t.Lambda;
t.Phi = tb.Phi - t.Phi;
do
{
del = NadInterpolate(t, table);
/* This case used to return failure, but I have
changed it to return the first order approximation
of the inverse shift. This avoids cases where the
grid shift *into* this grid came from another grid.
While we aren't returning optimally correct results
I feel a close result in this case is better than
no result. NFW
To demonstrate use -112.5839956 49.4914451 against
the NTv2 grid shift file from Canada. */
if (del.Lambda == HUGE_VAL)
{
System.Diagnostics.Debug.WriteLine(ProjectionMessages.InverseShiftFailed);
break;
}
t.Lambda -= dif.Lambda = t.Lambda - del.Lambda - tb.Lambda;
t.Phi -= dif.Phi = t.Phi + del.Phi - tb.Phi;
} while (i-- > 0 && Math.Abs(dif.Lambda) > TOL && Math.Abs(dif.Phi) > TOL);
if (i < 0)
{
System.Diagnostics.Debug.WriteLine(ProjectionMessages.InvShiftConvergeFailed);
t.Lambda = t.Phi = HUGE_VAL;
return t;
}
input.Lambda = Proj.Adjlon(t.Lambda + table.LowerLeft.Lambda);
input.Phi = t.Phi + table.LowerLeft.Phi;
}
else
{
if(t.Lambda == HUGE_VAL)
{
input = t;
}
else
{
input.Lambda -= t.Lambda;
input.Phi += t.Phi;
}
}
return input;
}
