Indexing astronomical database tables using HTM and HEALPix

TL;DR

This paper presents a method for indexing astronomical database tables using HTM and HEALPix schemas, integrated into MySQL via the MCS library to facilitate efficient data retrieval and analysis.

Contribution

It introduces a MySQL-compatible implementation of HTM and HEALPix indexing through the MCS library's DIF package, enabling transparent handling of large astronomical datasets.

Findings

Supports up to 1 billion objects in catalogues

Provides MySQL-callable functions for HTM and HEALPix

Enables efficient cross-matching and subset selection

Abstract

In various astronomical projects it is crucial to have coordinates indexed tables. All sky optical and IR catalogues have up to 1 billion objects that will increase with forthcoming projects. Also partial sky surveys at various wavelengths can collect information (not just source lists) which can be saved in coordinate ordered tables. Selecting a sub-set of these entries or cross-matching them could be un-feasible if no indexing is performed. Sky tessellation with various mapping functions have been proposed. It is a matter of fact that the astronomical community is accepting the HTM and HEALPix schema as the default for object catalogues and for maps visualization and analysis, respectively. Within the MCS library project, we have now made available as MySQL-callable functions various HTM and HEALPix facilities. This is made possible thanks to the capability offered by MySQL 5.1 to add external plug-ins. The DIF (Dynamic Indexing Facilities) package distributed within the MCS library, creates and manages a combination of Views, Triggers, DB-engine and plug-ins allowing the user to deal with database tables indexed using one or both these pixelisation schema in a completely transparent way.