[Kstars-devel] Binary file format for NOMAD

[Jan Kotek]

Hi,
two points

1) Catalog number of star. I am not sure, but it is probably made by
plate number + record number in file. If you reindex it, you propably
lose plate number

2) USNO guys are little alergic for distributing reindexed/remastered
catalog, Stellarium guys had some talk with them. 

jan

On Tue, 2008-07-15 at 17:21 +0530, Akarsh Simha wrote:
> Hi
> 
> NOMAD data can be compressed to take up 14 ~ 16 bytes, because it
> doesn't have a lot of information that forced us to use the 32-byte
> structure earlier.
> 
> Since size is almost the primary concern for the 1e8 and 1e9 catalogs,
> I think it would be worth changing the code to use 16-bytes per star.
> 
> The organization of data will be very straightforward:
> 
> +------------------------+--------------------------+
> |    Right Ascension     |        Declination       |
> |       4 bytes          |          4 bytes         |
> +----------+-------------+-------------+------------+
> |  RM RA   |   PM Dec    |  Blue Mag   |  Vis. Mag  |
> | 2 bytes  |  2 bytes    |  2 bytes    |  2 bytes   |
> +----------+-------------+-------------+------------+
> 
> We could get the spectral type from B-V within the program. This will
> make sure we don't lose any information, in case we would want to base
> our colours on B-V or display B and V magnitudes at some point of
> time.
> 
> While we could further reduce the size of the block by about 2 bytes
> by squeezing in about 3 bits somewhere to indicate whether the star is
> of B, A, F, G, K, M spectral classes, this would increase the
> complexity of the program that reads and interprets the data. Besides,
> this will reduce the final file size by about 12.5% (80MB to 70MB?),
> which I don't think is worth the additional effort. Maybe we could
> start supporting a 14 bytes per record format sometime in the future,
> (when we would want to support the USNO A binary format, the formats
> used by other popular desktop planetariums) and just version it off
> differently.
> 
> I'll start working on the 16 byte structure now, and I don't mind
> backtracking if someone has a better idea.
> 
> Regards
> Akarsh
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