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/OpenLayers/Layer/GoogleMercator.js?rev=3791
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.
