Created
January 13, 2010 14:02
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object GeoHash{ | |
val base32 = "0123456789bcdefghjkmnpqrstuvwxyz" | |
def encode( longtitude:Double, latitude:Double, range:Double) = { | |
def asBit( d:Double,max:Double,min:Double ) : List[Boolean] = { | |
val mid = ( max + min ) / 2 | |
var res = ( d >= mid ) | |
val (m,n) = if( res ) (max,mid) else (mid,min) | |
if( Math.abs( m - n ) <= range ) | |
res :: Nil | |
else | |
res :: asBit( d ,m ,n ) | |
} | |
def asBase32( xs:List[Boolean] ):String = { | |
base32( (0.0 /: xs.reverse.zipWithIndex){ | |
case( n,(b,i) ) => if( b ) n + Math.pow( 2, i ) else n | |
} toInt | |
).toString | |
} | |
def encodeBits( xs:List[Boolean] ):String = xs match{ | |
case Nil => "" | |
case _ => | |
val (h,t) = xs.splitAt(5) | |
asBase32(h) + encodeBits( t ) | |
} | |
val bits = asBit(longtitude , 180,-180 ). | |
zipAll( asBit( latitude, 90, -90 ), false, false ). | |
flatMap{ case (a,b) => a::b::Nil } | |
encodeBits( bits ).reverse.dropWhile( '0' == ).reverse.mkString | |
} | |
def decode( geohash:String ):((Double,Double),(Double,Double)) = { | |
def toBitList( s:String ) = s.flatMap{ | |
c => ("00000" + base32.indexOf(c).toBinaryString ). | |
reverse.take(5).reverse.map('1' == ) } toList | |
def split( l:List[Boolean] ):(List[Boolean],List[Boolean]) ={ | |
l match{ | |
case Nil => (Nil,Nil) | |
case x::Nil => ( x::Nil,Nil) | |
case x::y::zs => val (xs,ys) =split( zs );( x::xs,y::ys) | |
} | |
} | |
def dehash( xs:List[Boolean], min:Double, max:Double ):(Double,Double) = { | |
((min,max) /: xs ){ | |
case ((min,max) ,b) => | |
if( b )( (min + max )/2 , max ) | |
else ( min,(min + max )/ 2 ) | |
} | |
} | |
val ( xs ,ys ) = split( toBitList( geohash ) ) | |
( dehash( xs, -180,180 ) , dehash( ys ,-90,90) ) | |
} | |
} |
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