I'm working on an SQLite solution to get at star catalogs; they are usually searched via Right Ascension (RA), Declination (DEC), and magnitude (mag). RA,DEC is a spherical coordinate system to specify a star position on-sky; magnitude is related to star brightness.
What I have so far is here: https://github.com/drbitboy/Tycho2_SQLite_RTree I started with the Tycho-2 star catalog. It comprises 2.5 million stars in a flat ASCII, fixed-width catalog file (actually two files but ignore that for now), and an index file (map) of ~10k small RA-DEC regions, with an average of ~250 stars in each region. The regions do not overlap, and all the stars in any one region are in contiguous lines in the catalog file. The index file does not implement any grouping or sorting by magnitude. Each index region refers to A) a contiguous region on-sky with defined by a min-max RA pair and a min-max DEC pair. B) a contiguous range of the lines (stars) in the flat file that are within that region. So the data in the index file are a reasonable starting point for an R*Tree in SQLite3. I put the index file data into the virtual table using the RA and DEC limits for each region as the two min-max pairs of columns in the table, and the index table, referenced by the primary key of the virtual table, contains the starting and ending+1 indices (offsets actually) of the stars in the flat catalog file for each region. So I use the R*Tree module to get a fast lookup into the index table, returning index regions that overlap an input RA and DEC min-max pair, then step through the catalog lines for each of those regions. Here's my question: is there any advantage to skipping the index step and putting the star catalog data into the virtual table itself? One advantage is that I could include the magnitude in the rtree table. The reason I ask is that rtree table uses min-max pairs, but each star is a point so the min and max are equal for each star. Would that break any implicit R*Tree rules or negate any efficiencies? Thanks, Brian Carcich _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
