Montage is a toolkit for assembling astronomical images into mosaics. Its scientific value derives from three features of its design:
- It uses algorithms that preserve the calibration and positional (astrometric) fidelity of the input images to deliver mosaics that meet user-specified parameters of projection, coordinates, and spatial scale. It supports all projections and coordinate systems in use in astronomy.
- It contains independent modules for analyzing the geometry of images on the sky, and for creating and managing mosaics; these modules are powerful tools in their own right and have applicability outside mosaic production, in areas such as data validation.
- It is written in American National Standards Institute (ANSI)-compliant C, and is portable and scaleable - the same engine runs on desktops, clusters or supercomputer environments running common Unix-based operating systems.
There are four steps in the production of an image mosaic:
- Discover the geometry of the input images on the sky from the input FITS keywords and use it to calculate the geometry of the output mosaic on the sky
- Re-project the input images to the same spatial scale, coordinate system, WCS projection, and image rotation
- Model the background radiation in the input images to achieve common flux scales and background levels across the mosaics
- Co-add the re-projected, background-corrected images into a mosaic
Each production step has been implemented as an independent module run from an executive script. This toolkit design offers flexibility to users. They may, for example, use Montage as a re-projection tool, or deploy a custom background rectification algorithm while taking advantage of the re-projection and co-addition engines.