Question

I have got long/lat coordinates with altitude in SQLite database.

Some example data:

latitude   longitude  altitude
------------------------------
48.003333  11.0       652    
48.036667  11.000833  651
48.280833  11.000833  533

Now i want some SQL query which will give me closest altitude to given latitude/longitude coordinates so for example

Given lat/long will be 48.023445/11.000733 so the closest is altitude 651 with lat/long 48.036667/11.000833. Tried to search a lot of forums but nothing usefull. Everywhere are examples on one variable or very slow queries. I need this query really fast and saw some solution based on UNIONS. I need it fast because i will make about 1,5 milions of queries on this table. I am using transactions and indexing.

Answer 1

I would go with something similar the following query:

select * from pos order by ((lat-48.00333)*(lat-48.00333)+(long-11.0)*(long-11.0)+(alt-652)*(alt-652));

SQLite does not support SQRT but as SQRT is monotonous you can skip it in the distance formula.