Interpolating at a single point

Slowness

Natgrid provides for interpolation at a single point but, as indicated and documented in the efficiency module, interpolation at single points is very expensive and, in general, should be used only for filling in a few missing data values.

How to do it

For the same input dataset, in order to avoid having to calculate the natural neighbor relationships every time interpolation is done on a single point, interpolation at single points is implemented as a three step process:

Invoke an initialization procedure that calculates the natural neighbor relationships. This procedure is NNPNTINITS in Fortran and c_nnpntinits in C.
Do the interpolation at the desired points. The procedure for this is NNPNTS in Fortran and c_nnpnts in C.
Terminate single point mode. This is done using the procedure NNPNTEND in Fortran and c_nnpntend in C.

You can set any control parameters you want before interpolating at individual points, except slopes and aspects cannot be calculated while in single point mode.

See Example 6 for Fortran and C examples of interpolation in single point mode.

Due to implementation details, the values calculated in single point mode may differ slightly from values at the same coordinates when calculated using a grid.