On Wed, 12 Nov 2008, Tomas Kolda wrote: > Integer has better precision if you are far from zero, because floats > use only 24 bits for significant, other bits is for sign and exponent. > So 32 bit integer is better if you know extends (-180, .... 180). Min > and max of int is -2.1e9 to 2.1e9. So if you multiply longitude and > latitude by 1e7 you get almost maximum from 32bit int in all range (from > -1.8e9 to 1.8e9). > > It is also faster to process. And if you are doing some difference > compression, it is easier to do with ints.
Integers are only a better precision if all the bits are used. Thus only improve the situation if a multiplication with 2^32 / 360 is used. Now the minor detail is that this operation has an error of 10^-7, but the more preciese the input the better the storage resolution. 89 * (2^32 / 360) 1061811359.28889 ---> 1061811359 1061811359 / (2^32 / 360) ---> 1061811359 * 360 / 2^32 (bit shift) 88.9999999757856 So what you suggest is also a naive method; but that method just killed the most significant 10^-8 digit. Basically it says; 360.0000000 =/ 3600000000 Now what was mentioned before; is the hard cut of a problem? Not if the input is typically only significant till 10^-6. Should we overmodel it now? Probably not until we have data that is that significant. Stefan _______________________________________________ dev mailing list [email protected] http://lists.openstreetmap.org/listinfo/dev
