The Transformer manages the regridding (also called the interpolation) of the coupling fields, i.e. the expression on the target component model grid of a coupling field given by a source component model on its grid. The Transformer performs only the weights calculation and the regridding per se. As explained in section 5.5.1, the neighbourhood search, i.e. the determination for each target point of the source points that will contribute to the calculation of its regridded value, is performed in parallel in the source PSMILe.
The Transformer can be assimilated to an automate that reacts following predefined sequences of actions considering what is demanded. The implementation of the Transformer is based on a loop over the receptions of predefined arrays of 11 Integers sent by the component PSMILe . These 11 integers give a clear description of what has to be done by the Transformer. The Transformer is thus able to react with a pre-defined sequence of actions matching the corresponding sequence activated on the sender side.
The first type of action that can be requested by the component PSMILe is to receive the grid information resulting of the different neighbouring searches. The Transformer receives, for each intersection of source and target process calculated by the PSMILe , the latitude, longitude, mask, or areas of all source and target grid points in the intersection involved in the regridding (EPIOS and EPIOT, see section 5.5.1). The Transformer then calculates the weight corresponding to each source neighbour depending on the regridding method chosen by the user. The end of this phase corresponds in the component models to the PSMILe routine prism_enddefcall.
During the simulation timestepping, the Transformer receives orders from the PSMILe linked to the different component processes to receive data for transformation (source component process) or to send transformed data (target component process). After a reception, the Transformer applies the appropriate transformations or regridding following the information collected during the initialisation phase (here, the regridding corresponds to applying the pre-calculated weights to the source field). In case of request of fields, the Transformer is able to control if the requested field has already been received and transformed. If so, the data field is sent; if not, the data field will be sent as soon as it is received and treated.
At the end of the run, the participating processes inform the Transformer once they are ready to finish the coupled simulation so that they all terminate collectively.