One of the questions we are often asked is what is the difference between Montage and the mosaic capabilities offered by the Skyview Virtual Telescope at NASA’s High Energy Astrophysics Archive Research Center.
My colleague John Good, the Montage architect, describes the difference as follows:
“Montage is much more slavishly flux conserving than Skyview. By default Skyview uses an interpolation between neighbor input pixels to determine the output value of a pixel. It only has one mode that is close to flux conserving and this only works exactly for certain projections where pixel edges can be treated as straight lines even after reprojection (though not a bad approximation most of the time).
Montage has been extensively tested and shown to conserve flux (to the floating-point round-off limit) for all projections. Pixel edges are treated as spherical coordinate curves. Also, reprojected areas for fractional pixels are preserved exactly so there are no edge effects at all when mosaicking.
Montage can be used with all standard projections in the WCS libraries. Going by the Skyview documentation, it only supports seven. Similarly, Skyview only supports a few specific coordinate systems while Montage allows full precession (e.g. Ecliptic B1983.5 -> Equatorial J2011.0).
Montage includes an extensive set of tools for background matching over the complete set of overlapping input images based on an iterative relaxation technique
Montage is written in C for speed. The newer version of Skyview is written in Java. When dealing with complex spherical trigonometry, C is much faster. Skyview often looks fast, but this is mostly due to the default resampling and background handling.
Finally, Montage is broken down into a set of modules that can be
run intependantly and processing can therefore be heavily parallelized with very little effort. In fact, Montage has been used extensively by the IT community to test large-scale parallelization and workflow environments.”