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# PDAFomi_get_interp_coeff_tri

This page documents the routine `PDAFomi_get_interp_coeff_tri`

of PDAF-OMI.

The routine is called in `init_dim_obs_OBSTYPE of an obseration module to initialize interpolation coefficients for triangular interpolation
with barycentric coordinates. It is used if the observation operator performs linear interpolation (usually `PDAFomi_obs_op_interp_lin`

).

See the page describing PDAF-OMI observation operators for a general overview. |

The interface is:

SUBROUTINE PDAFomi_get_interp_coeff_tri(gcoords, ocoords, icoeff) REAL, INTENT(in) :: gcoords(:,:) ! Coordinates of grid points; dim(3,2) ! 3 rows; each containing lon and lat coordinates REAL, INTENT(in) :: ocoords(:) ! Coordinates of observation; dim(2) REAL, INTENT(inout) :: icoeff(:) ! Interpolation coefficients; dim(3)

**Note:**

- In the array
`gcoords`

, the first index specifies the grid point while the second specifies the coordinate, thus`gcoords(1,1)`

is the first coordinate for grid point 1,`gcoords(1,2)`

is the second coordiate for grid point 1, while`gcoords(2,1)`

is the first coordiate for grid point 2. The coordinates need to be consistent with the indices specified in`thisobs%id_obs_p`

since these specify the elements of the state vector that are interpolated. Only the first`n_dim`

entries of ocoord will be used for the interpolation.