dms.js

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  */
/*  Geodesy representation conversion functions                       (c) Chris Veness 2002-2015  */
/*   - www.movable-type.co.uk/scripts/latlong.html                                   MIT Licence  */
/*                                                                                                */
/*  Sample usage:                                                                                 */
/*    var lat = Dms.parseDMS('51° 28′ 40.12″ N');                                                 */
/*    var lon = Dms.parseDMS('000° 00′ 05.31″ W');                                                */
/*    var p1 = new LatLon(lat, lon);                                                              */
/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  */

'use strict';


/**
 * Tools for converting between numeric degrees and degrees / minutes / seconds.
 *
 * @namespace
 */
var Dms = {};


// note Unicode Degree = U+00B0. Prime = U+2032, Double prime = U+2033


/**
 * Parses string representing degrees/minutes/seconds into numeric degrees.
 *
 * This is very flexible on formats, allowing signed decimal degrees, or deg-min-sec optionally
 * suffixed by compass direction (NSEW). A variety of separators are accepted (eg 3° 37′ 09″W).
 * Seconds and minutes may be omitted.
 *
 * @param   {string|number} dmsStr - Degrees or deg/min/sec in variety of formats.
 * @returns {number} Degrees as decimal number.
 */
Dms.parseDMS = function(dmsStr) {
    // check for signed decimal degrees without NSEW, if so return it directly
    if (typeof dmsStr == 'number' && isFinite(dmsStr)) return Number(dmsStr);

    // strip off any sign or compass dir'n & split out separate d/m/s
    var dms = String(dmsStr).trim().replace(/^-/, '').replace(/[NSEW]$/i, '').split(/[^0-9.,]+/);
    if (dms[dms.length-1]=='') dms.splice(dms.length-1);  // from trailing symbol

    if (dms == '') return NaN;

    // and convert to decimal degrees...
    var deg;
    switch (dms.length) {
        case 3:  // interpret 3-part result as d/m/s
            deg = dms[0]/1 + dms[1]/60 + dms[2]/3600;
            break;
        case 2:  // interpret 2-part result as d/m
            deg = dms[0]/1 + dms[1]/60;
            break;
        case 1:  // just d (possibly decimal) or non-separated dddmmss
            deg = dms[0];
            // check for fixed-width unseparated format eg 0033709W
            //if (/[NS]/i.test(dmsStr)) deg = '0' + deg;  // - normalise N/S to 3-digit degrees
            //if (/[0-9]{7}/.test(deg)) deg = deg.slice(0,3)/1 + deg.slice(3,5)/60 + deg.slice(5)/3600;
            break;
        default:
            return NaN;
    }
    if (/^-|[WS]$/i.test(dmsStr.trim())) deg = -deg; // take '-', west and south as -ve

    return Number(deg);
};


/**
 * Converts decimal degrees to deg/min/sec format
 *  - degree, prime, double-prime symbols are added, but sign is discarded, though no compass
 *    direction is added.
 *
 * @private
 * @param   {number} deg - Degrees to be formatted as specified.
 * @param   {string} [format=dms] - Return value as 'd', 'dm', 'dms' for deg, deg+min, deg+min+sec.
 * @param   {number} [dp=0|2|4] - Number of decimal places to use – default 0 for dms, 2 for dm, 4 for d.
 * @returns {string} Degrees formatted as deg/min/secs according to specified format.
 */
Dms.toDMS = function(deg, format, dp) {
    if (isNaN(deg)) return null;  // give up here if we can't make a number from deg

    // default values
    if (format === undefined) format = 'dms';
    if (dp === undefined) {
        switch (format) {
            case 'd':    case 'deg':         dp = 4; break;
            case 'dm':   case 'deg+min':     dp = 2; break;
            case 'dms':  case 'deg+min+sec': dp = 0; break;
            default:    format = 'dms'; dp = 0;  // be forgiving on invalid format
        }
    }

    deg = Math.abs(deg);  // (unsigned result ready for appending compass dir'n)

    var dms, d, m, s;
    switch (format) {
        default: // invalid format spec!
        case 'd': case 'deg':
            d = deg.toFixed(dp);    // round degrees
            if (d<100) d = '0' + d; // pad with leading zeros
            if (d<10) d = '0' + d;
            dms = d + '°';
            break;
        case 'dm': case 'deg+min':
            var min = (deg*60).toFixed(dp); // convert degrees to minutes & round
            d = Math.floor(min / 60);       // get component deg/min
            m = (min % 60).toFixed(dp);     // pad with trailing zeros
            if (d<100) d = '0' + d;         // pad with leading zeros
            if (d<10) d = '0' + d;
            if (m<10) m = '0' + m;
            dms = d + '°' + m + '′';
            break;
        case 'dms': case 'deg+min+sec':
            var sec = (deg*3600).toFixed(dp); // convert degrees to seconds & round
            d = Math.floor(sec / 3600);       // get component deg/min/sec
            m = Math.floor(sec/60) % 60;
            s = (sec % 60).toFixed(dp);       // pad with trailing zeros
            if (d<100) d = '0' + d;           // pad with leading zeros
            if (d<10) d = '0' + d;
            if (m<10) m = '0' + m;
            if (s<10) s = '0' + s;
            dms = d + '°' + m + '′' + s + '″';
        break;
    }

    return dms;
};


/**
 * Converts numeric degrees to deg/min/sec latitude (2-digit degrees, suffixed with N/S).
 *
 * @param   {number} deg - Degrees to be formatted as specified.
 * @param   {string} [format=dms] - Return value as 'd', 'dm', 'dms' for deg, deg+min, deg+min+sec.
 * @param   {number} [dp=0|2|4] - Number of decimal places to use – default 0 for dms, 2 for dm, 4 for d.
 * @returns {string} Degrees formatted as deg/min/secs according to specified format.
 */
Dms.toLat = function(deg, format, dp) {
    var lat = Dms.toDMS(deg, format, dp);
    return lat===null ? '–' : lat.slice(1) + (deg<0 ? 'S' : 'N');  // knock off initial '0' for lat!
};


/**
 * Convert numeric degrees to deg/min/sec longitude (3-digit degrees, suffixed with E/W)
 *
 * @param   {number} deg - Degrees to be formatted as specified.
 * @param   {string} [format=dms] - Return value as 'd', 'dm', 'dms' for deg, deg+min, deg+min+sec.
 * @param   {number} [dp=0|2|4] - Number of decimal places to use – default 0 for dms, 2 for dm, 4 for d.
 * @returns {string} Degrees formatted as deg/min/secs according to specified format.
 */
Dms.toLon = function(deg, format, dp) {
    var lon = Dms.toDMS(deg, format, dp);
    return lon===null ? '–' : lon + (deg<0 ? 'W' : 'E');
};


/**
 * Converts numeric degrees to deg/min/sec as a bearing (0°..360°)
 *
 * @param   {number} deg - Degrees to be formatted as specified.
 * @param   {string} [format=dms] - Return value as 'd', 'dm', 'dms' for deg, deg+min, deg+min+sec.
 * @param   {number} [dp=0|2|4] - Number of decimal places to use – default 0 for dms, 2 for dm, 4 for d.
 * @returns {string} Degrees formatted as deg/min/secs according to specified format.
 */
Dms.toBrng = function(deg, format, dp) {
    deg = (Number(deg)+360) % 360;  // normalise -ve values to 180°..360°
    var brng =  Dms.toDMS(deg, format, dp);
    return brng===null ? '–' : brng.replace('360', '0');  // just in case rounding took us up to 360°!
};


/**
 * Returns compass point (to given precision) for supplied bearing.
 *
 * @param   {number} bearing - Bearing in degrees from north.
 * @param   {number} [precision=3] - Precision (cardinal / intercardinal / secondary-intercardinal).
 * @returns {string} Compass point for supplied bearing.
 *
 * @example
 *   var point = Dms.compassPoint(24);    // point = 'NNE'
 *   var point = Dms.compassPoint(24, 1); // point = 'N'
 */
Dms.compassPoint = function(bearing, precision) {
    if (precision === undefined) precision = 3;
    // note precision = max length of compass point; it could be extended to 4 for quarter-winds
    // (eg NEbN), but I think they are little used

    bearing = ((bearing%360)+360)%360; // normalise to 0..360

    var point;

    switch (precision) {
        case 1: // 4 compass points
            switch (Math.round(bearing*4/360)%4) {
                case 0: point = 'N'; break;
                case 1: point = 'E'; break;
                case 2: point = 'S'; break;
                case 3: point = 'W'; break;
            }
            break;
        case 2: // 8 compass points
            switch (Math.round(bearing*8/360)%8) {
                case 0: point = 'N';  break;
                case 1: point = 'NE'; break;
                case 2: point = 'E';  break;
                case 3: point = 'SE'; break;
                case 4: point = 'S';  break;
                case 5: point = 'SW'; break;
                case 6: point = 'W';  break;
                case 7: point = 'NW'; break;
            }
            break;
        case 3: // 16 compass points
            switch (Math.round(bearing*16/360)%16) {
                case  0: point = 'N';   break;
                case  1: point = 'NNE'; break;
                case  2: point = 'NE';  break;
                case  3: point = 'ENE'; break;
                case  4: point = 'E';   break;
                case  5: point = 'ESE'; break;
                case  6: point = 'SE';  break;
                case  7: point = 'SSE'; break;
                case  8: point = 'S';   break;
                case  9: point = 'SSW'; break;
                case 10: point = 'SW';  break;
                case 11: point = 'WSW'; break;
                case 12: point = 'W';   break;
                case 13: point = 'WNW'; break;
                case 14: point = 'NW';  break;
                case 15: point = 'NNW'; break;
            }
            break;
        default:
            throw new RangeError('Precision must be between 1 and 3');
    }

    return point;
};


/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  */


/** Polyfill String.trim for old browsers
 *  (q.v. blog.stevenlevithan.com/archives/faster-trim-javascript) */
if (String.prototype.trim === undefined) {
    String.prototype.trim = function() {
        return String(this).replace(/^\s\s*/, '').replace(/\s\s*$/, '');
    };
}


/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  */
if (typeof module != 'undefined' && module.exports) module.exports = Dms; // CommonJS (Node)
if (typeof define == 'function' && define.amd) define([], function() { return Dms; }); // AMD