private static PhiLam Convert(PhiLam input, bool inverse, NadTable table)
{
if (input.Lambda == HUGE_VAL)
{
return(input);
}
// Normalize input to ll origin
if (!table.Filled)
{
table.FillData();
}
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)
{
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)
{
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);
}
