GPS coordinates of tile corners

[ad...@svk-zw.de]

Hey there,

I' ve searched the hole web, but I think I am not good enough in most
script languages.
What I need is a program where I can entere the center-coordinates of
the google map tile, and the wanted zoom level. The program has to
calculate the gps coordinates of 2 corners (bsp. Upper-left, lower-
right) and give them back.
Example [ullong, ullat, lrlong, lrlat] = gpscorners(long, lat,
zoomelevel)

I've found this one here, but I don't know how to use it.

import java.applet.*;
import java.awt.*;
import java.lang.*;

public class Googlecoordinates

{


/**
* returns a Rectangle2D with x = lon degrees , y = lat degrees,
* width=lonSpan, height=latSpan
* for an x,y,zoom as used by google.
*/
public static Rectangle2D.Double getLatLong(int x, int y, int
zoom)
{
double lon = -180; // x
double lonWidth = 360; // width 360


//double lat = -90; // y
//double latHeight = 180; // height 180
double lat = -1;
double latHeight = 2;


int tilesAtThisZoom = 1 << (17 - zoom);
lonWidth = 360.0 / tilesAtThisZoom;
lon = -180 + (x * lonWidth);
latHeight = -2.0 / tilesAtThisZoom;
lat = 1 + (y * latHeight);


// convert lat and latHeight to degrees in a mercator
projection
// note that in fact the coordinates go from
// about -85 to +85 not -90 to 90!
latHeight += lat;
latHeight = (2 * Math.atan(Math.exp(Math.PI * latHeight))) -
(Math.PI / 2);
latHeight *= (180 / Math.PI);


lat = (2 * Math.atan(Math.exp(Math.PI * lat))) - (Math.PI / 2);
lat *= (180 / Math.PI);


latHeight -= lat;


if (lonWidth < 0) {
lon = lon + lonWidth;
lonWidth = -lonWidth;
}


if (latHeight < 0) {
lat = lat + latHeight;
latHeight = -latHeight;
}


return new Rectangle2D.Double(lon, lat, lonWidth, latHeight);
}

}


Hope you can help me. Thanks for your time!

[Nathan Raley]

You know the size of your container.  You know the center lat.  You can convert the center lat to pixel, adjust to top-left and bottom-right respectively, then convert from pixel to coordinates.

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[ad...@svk-zw.de]

Hi,

thanks for your answer,
I tried a little and I can find the corner coordiantes only for
longitude,.

but @ latitude I don't know the lat length of my tile.... so how can i
get those?

again, thanks for your help.

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[Nathan Raley]

Every tile is 256x256.  Convert your center lat,lon to pixels and then adjust accordingly to get the lat,lon of your corners.  Remember 0,0 is top left most tile coordiantes.

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