Since all of these calculations are planar and near estimates, perhaps it would be good to use libraries that particularly cope with "geospatial operations"
perhaps GOES might be a good starting point: http://trac.osgeo.org/geos/ Kind regards, Milo "Don't reinvent wheels, make beautiful cars!" Rogier Wolff wrote: > On Fri, Aug 08, 2008 at 04:02:10PM +0100, David Earl wrote: >> On 08/08/2008 14:30, Fire Girl wrote: >>> I am working with OSM data, and would like to be able to spec out 5 mile >>> bounding boxes from certain GPS points. >>> >>> After research into this problem, I am to understand that each degree of >>> latitude is approximately 69 miles (111 kilometers) apart with a slight >>> variance (68.703 - 69.407 miles) between the equator and the poles, and >>> that each degree of longitude is widest at the equator @ 69.172 miles >>> (111.321 kilometers) and gradually shrinks to zero at the poles. : ) :) >>> >>> So what does this mean? If I want to take a input point, like lets say, >>> >>> 167.9 lat >>> -29.1 lon >>> >>> or >>> >>> -63.1 >>> 18.1 >>> >>> Can someone say with authority, what the 'calculus' would be to >>> definitivly construct a NSWE bounding box with a 5 mile radius around >>> those points?.... that would be basically close enough or accurate? :) > > A degree longitude is about 40000km / 360 * cos (lat). > A degree lattitude is about 40000km / 360. > > So 5 miles would be in longitude: > 5 / (40000 / 1.609 / 360 * cos (lat)) > km/circle degrees/circle > mile km/mile > > and about > > 5 / (40000 / 1.609 / 360) > km/circle degrees/circle > mile km/mile > > lattidude. This comes to about 0.0725, 0.0725/cos(lat) degrees for > 5 miles (lat, lon). > > This defines an almost-square where the circle would be almost > completely inside. > > This especially doesn't work near the poles. > > Roger. > _______________________________________________ dev mailing list [email protected] http://lists.openstreetmap.org/listinfo/dev
