[OpenLayers-Users] resoloution and tile x and y

[Chris Adams]

if: pixel = tilexy * tilesize

and: res = ll / pixel

then: ll = res*pixel

if: tilesize = 300
and: tilexy is always offset by 0.5 (the center)

then:

lat = (tiley + 0.5) * 300 * res
lon = (tilex + 0.5) * 300 * res

but because we don't view the world upside down, i.e. latitude increases 
as y decreases..

lat = (-tiley + 0.5) * 300 * res
lon = (tilex + 0.5) * 300 * res

Kenny France wrote:
> Hi Guys,
>  
> Im finally getting somewhere with the help of Chris Adams (Thanks Again)
>  
> I have a map gererated, that is going to ultimatly grab image tiles 
> from my server
>  
> I now know that if my tile is 300 Px and i need a resoloution of 5,12 
> dd the calculation is
> 5.12 / 300 = 0.017066667
>  
> In my sample i am simply displaying the pink tiles for now, but it is 
> trying to pull from my url, using the getfile function in the example
>  
> so it shows get_tile.php?z=1&x=21&y=28
>  
> where z = zoom
> x = tile number in the x position
> y = tile number in the y position
>  
> No by knowing the zoom level tile number etc, how could i calculate 
> the center lat/lng of the tile needed?
> I thought it would be simple but how will i figure out if the lat/lng 
> are negitive values
>  
> Please help me once again
>  
> K-
>
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