[OSM-dev] Proposal: Database accelerator and dirty tile marker based on simple algorithm.

[Nick Hill]

The following code follows my worked example exactly:

uint64_t nickconvert_1E7(double lat, double lon){
uint64_t result; unsigned int intLat, intLon,count; double 
coefficient=10000000;
//First, we convert the number to an unsigned int where the MSB is 1 if 
negative
//the very low coefficients compensate for floating point rounding 
errors (pedantic=affirmative)
if(lat<0){intLat=(lat-0.000000001)*-1*coefficient+2147483648;}else{intLat=coefficient*(lat+0.000000001);}
if(lon<0){intLon=(lon-0.000000001)*-1*coefficient+2147483648;}else{intLon=coefficient*(lat+0.000000001);}
	for(count=(unsigned int)1<<31;count>0; count>>=1){
	   result<<=2;
	   result += (intLat & count ?2:0) + (intLon & count ? 1:0);
		}
	return result;
}


The following code will generate the quadtree tiles as I think you have 
in mind:

uint64_t nickconvert_quadtile(double lat, double lon){
	uint64_t result; unsigned int intLat, intLon,count;
	double coefficient=(2^32)/360;
	intLat=lat*coefficient; intLon=lon*coefficient;
	for(count=(unsigned int)1<<31;count>0; count>>=1){
		result<<=2;
		result += (intLat & count ?2:0) + (intLon & count ? 1:0);
		}
	return result;
}


The quadtile example may provide a convenient platform-created rollover 
at the edges.




Nick Hill wrote:
> Hello Nigel
> 
> You are correct in representing two approaches to the same problem. 
> Yours being to recursively sub-divide the planet, mine being to convert 
> the lat/lon values through binary manipulation to the same conclusion.
>