Jakub Ladman wrote:
I will have table with sequence of coordinates (two dimensional space) and
corresponding radiuses, so sequence of circles. And i need to use a sqlite
query to detect if a actual coordinates (after their measurement) match some
of the circle's square or not. And which circle, if match.
And this must be for low CPU consumption optimised, so i am not sure, if
separate sin table queries will be enough as fast as i need at needed
precission.
The whole algorithm is proven on mssql by my colegue, but he is using the
native math functions.
Jakub,
I may not understand your problem completely, but it seems to me you can
solve your problem without using any trigonometric functions.
If you have a table of circles like this
create table circle (
id integer primary key,
cx real,
cy real,
r real
);
You can find all the circles that contain a given point (px,py) using a
simple query based in the distance between the point and the center of
the circle.
select id from circle
where (px-cx)*(px-cx)+(py-cy)*(py-cy) < r*r;
If you want to create a user defined distance function you could
possibly speed up the calculation somewhat. You could then use a query like:
select id from circle
where distance(cx, cy, px, py) < r;
where
distance(cx, cy, px, py) = sqrt((px-cx)^2 + (py-cy)^2)
HTH
Dennis Cote
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