## Imaging Philosophy and Data Architecture

CASA intends to solve the Measurement Equation, whatever the complexity of this process. It is a all-in-one package for this purpose, where calibration and imaging are deeply intermixed and use a unified data format. As a result, a CASA Measurement Set is a complex architecture encompassing relations between many components stored as Tables in a directory-like tree. It can handle calibrated data, calibration tables, multisource data sets, raw data and final images in the same architecture, allowing to retain all information to process complex images, such as multi-frequency synthesis of polarized emission observed in a mosaic of fields.

On the contrary, GILDAS is designed to break the process in totally independent steps. For IRAM data, calibration is done in one program (CLIC for interferometry with NOEMA or CLASS for single-dish with the 30-m), and imaging in another (here IMAGER), with a clear intermediate step to change from the calibration data format (using the CLASSIC container) to UV Tables or CLASS Tables. In particular, IMAGER does not handle polarization transparently at the current time: polarization states must be imaged independently. The Gildas Data Format stores a limited number of informations in a single binary data file with a compact binary header, and is only suited for calibrated data. UV Tables are little more elaborate than simple images, but still limited in complexity.