Introduction
============

The aim of the SIM :term:`Processing Function` (developped by OU-SIM) is to produce homogeneous simulated data amongst the :term:`ECSGS` in a coordinated way for integration, validation and verification of the complexe :term:`ECSGS` framework. In addition, simulations produced by OU-SIM will also serve for the End to End performance validation of the entire Euclid mission.

Within the :term:`ECSGS`, the SIM PF is primarily responsible for producing simulated level-1 data for the 3 Euclid channels: VIS, NISP-P and NISP-S. Further, the SIM PF produces simulated level-EXT data: DES, KiDS, HSC and Gaia. Also, the SIM PF produces level-2 and level-3 data as processed by the OUs. The processing is emulated to produce idealized bypass data that can be used directly by OUs for debugging and optimisation of their algorithms, independently from the prior OU algorithms: SHE, MER, SPE, PHZ and LE3.

.. figure:: /figures/SIM_workflow.png

The SIM PF is divided into several :term:`Software Component`, which are combined inside the SIM :term:`Pipeline`. Interfaces between the different :term:`Processing Element` of the pipeline are file-based. In the figure below, only the data interfaces used by each component are shown. 

.. figure:: /figures/SIM_interfaces.png
 
In many cases, there are also metadata files involved, which we describe in the following subsection of the document:

* :ref:`WP-LE1`
* :ref:`WP-LE23`
* :ref:`WP-LEEXT`
* :ref:`WP-PLANNER`
* :ref:`WP-TU`