Gaia2 Quad Database Creator

The Gaia2 Quad Database Creator reads the output created by the Gaia2 Star Extractor and forms quads from the available stars, according to the parameters that you give to the program.

The creator outputs binary files in the format that is described in Quad Database. It forms several passes from the input stars, creating different densities of quads - lower densities contain bright stars only, and the higher the density, the dimmer stars are included. The more passes, the more quads are created. The smaller the pass factor, the smaller the step between densities.

Parameters example:

--input z:\gaia2stars --stars 20 --start-pass 0 --end-pass 7 --threads 10 --out z:\quaddb

The three main parameters to note are:

• --stars: how many stars per square degree to use in the first pass quad formation
• --start-pass and --end-pass: which passes to generate
• --passfactor: the base factor to use when increasing number of stars per pass. This number gets raised to the power [pass], i.e. passfactor^passNumber. The default value for this is sqrt(2) ~= 1.4142, which seems to be a pretty nice value.

So in the example case, we would get:

• Pass 1: 20 stars per square degree
• Pass 2: 20 * 1.4142^1 = 28 stars
• Pass 3: 20 * 1.4142^2 = 40 stars
• Pass 4: 20 * 1.4142^3 = 56 stars
• Pass 5: 80 stars
• Pass 6: 113 stars
• Pass 7: 160 stars
• Pass 8: 226 stars
• Pass 9: 320 stars
• Pass 10: 452 stars

We then start to form the passes. Depending on the density, we'll choose how many subdivisions / sub cells we want to have in each pass. The more stars, the more sub cells we split them into. We order the stars by magnitude, and include the top brightest stars to the cell until we reach the target star density. We then form quads from the stars in each pass, in each sub cell and write output of the cell file in the format described in Quad Database.

Things to note

The more star-dense passes you want to have, the more stars you will need. So you'll need to consider that when running the Gaia2 Star Extractor, if you choose a low magnitude limit it'll limit the densities you're able to produce. You can add as many passes as you like but when you run out of stars you'll simply get multiple passes with the same density.

This process is significantly faster than extracting the stars but still takes some time. Expect to spend hours to generate all the database files.