Have now got the right projection string working, thanks. However one thing I'd
like to clarify in my mind (and apologies if this is slightly OT) is what the
"Google Mercator projection units", as obtained by the code below, actually
represent. They do *not* appear to correspond to pixels at any given zoom
level: I've tested this on three nearby points on the Earth and the differences
in "Google projection units" between them do not appear to correspond exactly
to pixels at any given zoom level. So is there a simple arithmetic relation
between "Google projection units" and pixels at any given zoom level?
Thanks,
Nick
static EarthPoint fromLLToGoog(double lon,double lat)
{
double a = log(tan((90+lat)*M_PI / 360))/(M_PI / 180);
double custLat = a * 20037508.34 / 180;
double custLon=lon;
custLon = custLon * 20037508.34 / 180;
return EarthPoint(custLon,custLat);
}
// other way round
static EarthPoint fromGoogToLL(double x,double y)
{
double lat_deg,lon_deg;
lat_deg = (y / 20037508.34) * 180;
lon_deg = (x / 20037508.34) * 180;
lat_deg = 180/M_PI *
(2 * atan(exp(lat_deg * M_PI / 180)) - M_PI / 2);
return EarthPoint(lon_deg,lat_deg);
}
_______________________________________________
Mapnik-users mailing list
[email protected]
https://lists.berlios.de/mailman/listinfo/mapnik-users
