Concatenation of HealSparse Files

HealSparse contains a routine for concatenating (combining) multiple HealSparseMap files. If fitsio is available, this will be done in a memory-efficient way. In this way, multiple non-overlapping maps can be combined. This makes possible a simple parallelized scatter-gather approach to creating complex survey maps, where individual tiles are run independently, and then all combined at the end.

Using cat_healsparse_files()

The cat_healsparse_files() routine takes in a list of filename, and an output filename. The individual files must have the same nside_sparse, but may have different nside_coverage. The output file will have the same nside_coverage as the first input file unless otherwise specified.

By default, for speed, the code will not check that the input HealSparseMap files are non-overlapping (that is, that they do not share valid_pixels; they may share coverage in the coverage map). This can be checked.

If fitsio is available (recommended), the combination is not done in-memory. This behavior can be modified by the user by setting in_memory to True. However, if only is available for FITS interfacing, the concatenation can only be done in-memory (and the in_memory value should be overridden.

import healsparse

healsparse.cat_healsparse_files(file_list, outfile, check_overlap=False, clobber=False,
                                in_memory=False, nside_coverage_out=None)