Hello Gilles,
RE:
> I am discovering the Spatial Extensions features of MySQL-5.0
> Is there a way to use a spherical geometry ? (instead of Euclidean)
> like for navigation, or on sky coordinates,...
As far as MySQL-5.0, I have not found any such feature.
I believe it is available in the recent PostGres, but have not tried it.
In any case, so far we have quite disappointing experience with
MySQL-5.0 and geometry indexing.
First, the point() geometry sub-type (which is basically two doubles
glued together) is not fixed length, thus the table in which you have a
geometry column will be 'dynamic', and indexing and searching for other
columns becomes very slow. You can get around this by separate table
with geometry info, and join on tables.
Second, for big astronomical catalogues (10 million or more records),
we found that simple ascii/binary implementation on the disk in a well
arranged structure leads to much faster results.
For reference:
given a catalogue of 38million records.
geometry info is in a separate table, and it is indexed.
join is done on a primary key
we select data in a 10x10deg area
on dual opteron 2.0GHZ computer this is 5 to 20 seconds.
With an ascii catalogue manipulator this is at most 5sec, but
usually 1-2 seconds.
Third: indexing on geometry is very slow.
With *_buffer = 1Gb size (sort buffer = 256Mb) 100 millions record
indexing will take up to a week or more.
And finally, you can expect weird messages from mysqladmin.
E.g. mysqladmin --sort-index on the geometry table works for some
tables, and returns with unknown error for others (usu. when the num of
records is more than 10 million ?) See a previous posting of mine.
Cheers
Gaspar
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