14 Jun 09 Announcing GeoHashFlash!

Okay, so it's hardly an announcement, but I've been working on a flex app for determining your daily official xkcd meetup location via the geohashing method described in comic 426.

Much love to:

• Randall Munroe for beloved xkcd
• Google, for their lovely Maps API and documentation.
• Peeron for the help with the Dow Jones snapshots.
• Geoffrey Williams for his MD5 AS conversion

I'm still learning Flex and this is my first adventure with Google Map, so it's rough. And there's still a lot of work to do, like, validation, error checking, or testing for example. But hey, first pass!

Here's the code for the actual GeoHash class. I have "view source" disabled because it currently contains my API key, but you can download the key-less zip.

public class GeoHasher {

	private var date:Date;
	private var dow:Number;
	private var latitude:Number;
	private var longitude:Number;

	private var dateHash:String;
	private var dowHash:String;

	private var ready:Boolean;

	public function GeoHasher() {
		this.ready = false;
	}

	public function reset(
		date:Date,
		dow:Number,
		latitude:Number,
		longitude:Number
	):void {
		this.date      = date;
		this.dow       = dow;
		this.latitude  = latitude;
		this.longitude = longitude;

		this.ready     = true;

		setHashValues();
	}

	public function getDestination():Object {
		if(ready) {
			var hash:Object = getHashAsDecimal();
			return {
				latitude: toOrdinal(latitude, hash.date),
				longitude: toOrdinal(longitude, hash.dow)
			};
		}
		return { latitude: "", longitude: "" };
	}

	// privates

	private function setHashValues():void {
		var formattedDate:String = Utilities.dateFormat(date,"-");
		var string:String = formattedDate + "-" + dow.toString();
		var hash:String   = MD5.encrypt(string); 

		dateHash = hash.slice(0,hash.length / 2);
		dowHash  = hash.slice(hash.length / 2,hash.length);
	}

	private function toOrdinal(pre:Number, post:Number):String {
		return (Math.floor(pre) + post).toString();
	}

	private function getHash():Object {
		return { date: dateHash, dow: dowHash };
	}

	private function getHashAsDecimal():Object {
		var hash:Object = getHash();
		return {
				date: Utilities.fractionalHexToDecimal(hash.date),
				dow: Utilities.fractionalHexToDecimal(hash.dow)
		};
	}
}

Tags: actionscript, flex, geohashflash, geohashing, xkcd

public function fractionalHexToDecimal(hex:String):Number {
	var total:Number = 0;
	for(var i:int = 0; i < hex.length; i++) {
		total += (parseInt("0x" + hex.charAt(i)) / Math.pow(16,i+1));
	}
	return total;
}

fractionalHexToDecimal("1");
// 0.0625

fractionalHexToDecimal("0a");
// 0.0390625

fractionalHexToDecimal("db9318c2259923d0");
// 0.8577132677070023