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Interpolations with gl

Introduction

In the following we describe the geometrical routines in gl. gl can handle the following projections

  • lat/lon
  • Rotated lat/lon
  • Lambert
  • Polar stereographic
  • Rotated Mercator

Interpolation

All interpolations are handled within the module util/gl/mod/module_interpol.f90. The module contains

  • clear_interpol to clear the interpolation setup
  • setup_interpol where the position of the output gridpoints in the input grid are calculated
  • setup_weights where we calculate the interpolation weights. Interpolation can be nearest gridpoint or bilinear. The interpolation can be masked with a field that tells which gridpoints from the input fields that can be used.

The setup routines are only called once.

  • interpolate runs the interpolation
  • resample works like the interpolation if the input grid is coarser than the output grid. If reversed it takes the averages of the input gridpoints belonging to each output gridpoit.

Interpolation can be done between different projections as wall as to geographical points. The most general example on the usage of the interpolatin can be found in util/gl/grb/any2any.F90.

For practical usage see the section about postprocessing

Rotations

All rotations are handled within the module util/gl/mod/module_rotations.f90. The module contains

  • clear_rotation to clear the rotation setup
  • prepare_rotation prepare rotations from input geometry to output geometry via north south components.
  • rotate_winds runs the actual rotation.

Staggering

The staggering of an input file is based on the knowledge about the model and is in util/gl/mod/module_griblist.f90. The restaggering is done in util/gl/grb/restag.f90 as a simple average between gridpoints. The staggering of the output geomtery is defined by OUTGEO@ARKAWA, where A and C are available options.