Thanks, it is spherical mercator projection -> lat lon. I have done a simple solution for this , it seems to work. http://github.com/h4ck3rm1k3/GWTOsm/commit/51fb613e679d7a4ccb7ff8b74d41645397c48fbd
The program is now deployed and you can check it http://xhema.flossk.org:8180/GWTOSM/ It is very very simple, but finally is working. Now I can add in more features. mike On Jun 3, 2:16 pm, Brendan Kenny <bcke...@gmail.com> wrote: > Mike -- > > Eric is absolutely right, and I should have been more careful in my > initial response, but for your case you should be fine with that > simpler solution. > > Obviously I don't know what form that "EastNorth" object is going to > be or what you input data looks like, but (assuming that the function > fits your data and you take this advice with a large grain of salt) > your initial function call should be fine precision-wise. Since it > looks like you're just creating location markers based on where a user > clicks, and even assuming you'll need that down to a tenth of an > arcsecond, you'll need to be at ludicrously large zoom levels on the > map before you run into any precision problems. > > FWIW, > > Math.atan(Math.sinh(p.north()))*180/Math.PI > > is equivalent to (in this domain) > > (2 * Math.atan(Math.exp(p.north())) - Math.PI/2) * 180/Math.PI > > (similar to the second code sample you posted). That gets you around > using sinh() and might keep things a little neater numerically. > > With mapping, input noise will drown out a lot of other problems (the > assumption that the earth is a perfect sphere alone...), so I'd go > with the simple solution and just keep the rest in mind if you run > into problems further down the line. > > On Jun 2, 10:49 am, "jamesmikedup...@googlemail.com" > > <jamesmikedup...@googlemail.com> wrote: > > Hi all, > > I don't want to sound stupid, but I am not a mathematical genius. > > What i do know that is it taking a projected point (on the screen in > > Spherical Mercartor) to find out the lat long, > > > public LatLon eastNorth2latlon(EastNorth p) { > > return new LatLon( > > Math.atan(Math.sinh(p.north()))*180/Math.PI, > > p.east()*180/Math.PI); > > } > > > So the equivalent to this jsom code that I am porting is the open > > layers code. > > > I think this might be correct, but I am not certain. They look > > different. > > >http://trac.openlayers.org/browser/sandbox/crschmidt/google/lib/OpenL... > > > inverseMercator: function(merc) { > > 221 > > 222 var lon = (merc.lon / 20037508.34) * 180; > > 223 var lat = (merc.lat / 20037508.34) * 180; > > 224 > > 225 lat = 180/Math.PI * (2 * Math.atan(Math.exp(lat * > > Math.PI / 180)) - Math.PI / 2); > > 226 > > 227 return new OpenLayers.LonLat(lon, lat); > > 260 }, > > 261 > > > But this projection transformation is common, and also done by the > > google maps api. I will have to look into this some more. > > > thanks, > > mike > > On Jun 2, 4:37 pm, Eric <erjab...@gmail.com> wrote: > > > > On Jun 2, 4:21 am, Brendan Kenny <bcke...@gmail.com> wrote: > > > > > 2) or, if it needs to remain in js-land, just expose a sinh() function > > > > for use just like the page at your first link suggests: (e^x - e^(- > > > > x)) / 2. Just be careful with your NaNs and Infs. > > > > Actually, be careful with small values of x too. > > > e^x = 1 + x +x^2/2 + x^3/6 +..., but > > > sinh x = x + x^3 / 6 + .... > > > > Using e^x directly for small values of x automatically loses > > > significant digits. > > > The mathematical definition of a special function is rarely the way > > > you want > > > to compute it. Look up computational procedures in AMS 55, or the > > > Numerical Recipes series. You might find yourself using continued > > > fractions, > > > or Pade approximants. You almost certainly want to use different > > > procedures > > > for different values of x. > > > > Given that you have expm1 available, try sinh x = e^(-x) (e^(2x) - 1) / > > > 2 if you > > > have nothing else available: Math.exp(-x) * Math.expm1(2.0*x) / 2.0. > > > Switch > > > to the standard method when |x| > 0.1. But in any case, use e^(-x) = > > > 1/e^x. > > > > Look up AMS 55 (Abromowitz and Stegun), the Numerical Recipes series > > > (Press, et al), > > > and Numerical Methods that (Usually) Work (Acton). > > > > Why is the original poster using hyperbolic functions anyway? > > > > Respectfully, > > > Eric Jablow > > -- You received this message because you are subscribed to the Google Groups "Google Web Toolkit" group. To post to this group, send email to google-web-tool...@googlegroups.com. To unsubscribe from this group, send email to google-web-toolkit+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-web-toolkit?hl=en.
