= get_obs_f_pdaf =

The page document the user-supplied call-back routine `get_obs_f_pdaf`.

The routine `get_obs_f_pdaf` (called `U_get_obs_f` in the PDAF core routines) is a call-back routine that has to be provided by the user. 
This routine is used for generating synthetic observations with PDAF using [PDAF_generate_obs] or [PDAF_put_state_generate_obs].
The routine is called after PDAF has generated the observation. Here, PDAF provides the vector of synthetic observations to the user so that they can be stored, e.g. in a file.

The interface is the following:
{{{
SUBROUTINE get_obs_f_pdaf(step, dim_obs_f, observation_f)
}}}
with
 * `step` : `integer, intent(in)`[[BR]] Current time step
 * `dim_obs_f` : `integer, intent(in)`[[BR]] Size of the full observation vector
 * `observation_f` : `real, intent(out), dimension(dim_obs_f)`[[BR]] Full vector of synthetic observations (process-local)

Hints:
 * For the generation of synthetic observations, PDAF does not distinguish between local and global filters. Without parallelization, the full observation vector would be the same for both types of filters. With parallelization the implementation of the observation operator used for generating the observations will define whether different process-domain have the same or distinct observation vectors (i.e. covering the global domain or different process-specific domains). 
 * In case of the global filters, one uses the functionality of the observation operator for this filter type. With parallelization, the observation operator will initialize an observation vector specifically for each process-domain.
 * The usual operation performed in this routine is to write the generated synthetic observation into a file. The PDAF package provides the template routine [readwrite_obs readwrite_obs] for this. Depending on the parallelization, discussed above, one either writes a single file (of the full observation vector is the same for all processes. In this case one a single process calls the writing routine) or a different file for each process (in this case, each process call the routine with a different file name; usually indicating the process-rank number).