Interpolating at a single point


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:
  1. Invoke an initialization procedure that calculates the natural neighbor relationships. This procedure is NNPNTINITS in Fortran and c_nnpntinits in C.

  2. Do the interpolation at the desired points. The procedure for this is NNPNTS in Fortran and c_nnpnts in C.

  3. 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.

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