Alex Little

Spent the last couple of days trying to figure out why my clustering algorithm in Java wasn’t working properly – was working for some grids, but was totally messed up on others. I think I’ve tracked down why… the problem I think is to do with the precision of the datatypes I’m using in Java and MySQL. In Java I’m using the float type to store a latitude or longitude, then in the MySQL database I’m using decimal(15,12).

There appears to be a bit of a rounding problem somewhere along the line which I need to figure out. For some reason if I try and send a latitude of 52.2 from Java to be stored in the database, it gets stored as something like 52.2000007623. This means when I try and find all the points with latitude 52.2 it doesn’t pick up the record I’ve just inserted/updated.

I’ve not had much experience using this amount of decimal precision before, so the problems are probably due to my lack of understanding of the precision/accuracy of the various data types.

I think the way around this is to change my Java floats to be doubles for more precision and hopefully the problem won’t then occur  – not totally sure what to try if that doesn’t work, so please let me know if you have any suggestions