Grid Locator calculation code

gl.js

/*
 gl.js
 Grid Locator Calcuration Library
 version 1.0
 
 
 Copyright (C) 2013 Keisuke Nakao (chome@argv.org)
 
 This library is free software: you can redistribute is and/or modify
 it under the terms of the GNU General Public Licenses as published by
 the Free Software Foundation, version 2.
*/
 

/*
  指定した緯度経度から、グリッドロケーターを返す関数
  lat:  緯度 
  lng: 経度
*/
function calcGL(lat, lng){
    var char = function(n){return String.fromCharCode(0x41 + n)}
    var modf = function(n){return new Array(Math.floor(n), n - Math.floor(n))}

    var lng = modf(lng)
    var lat = modf(lat)

    return new Array(
	char(Math.floor((lng[0] + 180)/20.0)),
	char(Math.floor((lat[0] + 90.0)/10.0)),
	Math.floor((lng[0]%20)/2).toString(),
	Math.floor(lat[0]%10).toString(),
	char(Math.floor(((lng[0]%2) + lng[1])*60/5)),
	char(Math.floor(lat[1]*60/2.5))
    ).join("")
 }


/*
  指定したグリッドロケーターの北西の緯度経度を返す関数。
*/
function calcCorner(gl){
    var f = function(offset, unit, base)
    {
	return function(c)
	{
	    return (c.charCodeAt(0) - base.charCodeAt(0)) * unit - offset
	}
    }

    var fmap = new Array(f(180, 20, "A"), f(90, 10, "A"),
			 f(0, 2, "0"), f(0, 1, "0"),
			 f(0, 5.0/60.0, "A"), f(0, 2.5/60.0, "A")
    )

    // map
    var result = new Array()
    for(i=0; i<gl.length; i++){
	result.push(fmap[i](gl.charAt(i)))
    }

    // reduce
    return result.reduce(function(prev, curr, idx){
	if(idx%2 === 0){
	    return new Array(prev[0], prev[1] + curr)
	}else{
	    return new Array(prev[0] + curr, prev[1])
	}
    }, new Array(0,0))
}

/*
  指定したグリッドロケーターの南西と北東の緯度経度を返す関数
*/
function calcRect(gl)
{
    var sw = calcCorner(gl) // North-West
    var offset

    if(gl.length === 6){
	offset = new Array(2.5/60, 5.0/60)
    }else if(gl.length === 4){
	offset = new Array(1, 2)
    }else if(gl.length === 2){
	offset = new Array(10, 20)
    }else{
	return new Array(NaN, NaN)
    }
    return new Array(sw, new Array(sw[0] + offset[0], sw[1] + offset[1]))
}

// Test
// JARL HQ, 35.729, 139.7436, PM95UR  
//print(calcGL(35+43.0/60+45.0/3600, 139+44.0/60.0+37.0/3600))
//print(calcRect('PM95UR'))