[OSM-dev] How to translate coordinate to pixel for a tile ?

[Jon Burgess]

On Thu, 2007-11-15 at 22:50 +0100, Rune Baggetun wrote:
> This is how I tested the perl code:
> 
> #!/usr/bin/perl
> use Math::Trig;
> my $lon = 60.3434;
> my $lat = 5.2834;
> 
> my $z = 15;
> my $x = ($lon+180)/360 *2**$z * 256;
> my $y = (1 - log(tan($lat*pi/180) + sec($lat*pi/180))/pi)/2 *2**$z * 256;
> my $xtile = int($x/256);
> my $ytile = int($y/256);
> my $xpixel = $x % 256;
> print "$xpixel\n";
> my $ypixel = $y % 256;
> print "$ypixel\n";
> 
> 
> This is the output:
> 
> 151
> 105
> 
> This is actually the first piece of perl code I've written (or copied)
> so I am not surprised if I did something wrong. I do most my
> 'amateurish' coding in java and python.

Attached is a similar example written in python which shows what you get
with the lat/lon swapped:

$ ./coords.py
BAD
get( (60.343400000000003, 5.2834000000000003) 15 )
Tile: z( 15 ) x( 21876 ) y( 15902 ), offset( 151.0 , 105.0 )
Good
get( (5.2834000000000003, 60.343400000000003) 15 )
Tile: z( 15 ) x( 16864 ) y( 9452 ), offset( 232.0 , 249.0 )

	Jon

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