[OpenLayers-Users] Measure Distance? Ruler?
Chris Hardin
chrislhardin at gmail.com
Mon Aug 20 08:17:46 EDT 2007
Yeah, the calculation involves a little trig. I figure it would be an
easy feature to add. I use the following .js file to calculate it, I
just need to figure out how to feed it the starting point and ending
point and draw a line.
var EARTH_MEAN_RADIUS_MILES = 3959.87247;
var EARTH_MEAN_RADIUS_KILOMETERS= 6372.797;
var EARTH_MEAN_RADIUS_KNOTS =3441.0351;
var EARTH_MEAN_RADIUS_FEET = 20908126.6;
var EARTH_MEAN_RADIUS_METERS = 6372796.99;
var EARTH_MEAN_RADIUS_YARDS = 6969375.53;
/*
* Use Haversine formula to Calculate distance (in km) between two
points specified by
* latitude/longitude (in numeric degrees)
*
* example usage from form:
* result.value = LatLon.distHaversine(lat1.value.parseDeg(),
long1.value.parseDeg(),
* lat2.value.parseDeg(),
long2.value.parseDeg());
* where lat1, long1, lat2, long2, and result are form fields
*/
LatLon.distHaversine = function(lat1, lon1, lat2, lon2, meanRadius) {
var R = meanRadius;
var dLat = (lat2-lat1).toRad();
var dLon = (lon2-lon1).toRad();
lat1 = lat1.toRad(), lat2 = lat2.toRad();
var a = Math.sin(dLat/2) * Math.sin(dLat/2) +
Math.cos(lat1) * Math.cos(lat2) *
Math.sin(dLon/2) * Math.sin(dLon/2);
var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a));
var d = R * c;
return d;
}
/*
* ditto using Law of Cosines
*/
LatLon.distCosineLaw = function(lat1, lon1, lat2, lon2, meanRadius) {
var R = meanRadius;
var d = Math.acos(Math.sin(lat1.toRad())*Math.sin(lat2.toRad()) +
Math.cos(lat1.toRad())*Math.cos(lat2.toRad())*Math.cos((lon2-lon1).toRad()))
* R;
return d;
}
/*
* calculate (initial) bearing between two points
*
* from: Ed Williams' Aviation Formulary,
http://williams.best.vwh.net/avform.htm#Crs
*/
LatLon.bearing = function(lat1, lon1, lat2, lon2) {
lat1 = lat1.toRad(); lat2 = lat2.toRad();
var dLon = (lon2-lon1).toRad();
var y = Math.sin(dLon) * Math.cos(lat2);
var x = Math.cos(lat1)*Math.sin(lat2) -
Math.sin(lat1)*Math.cos(lat2)*Math.cos(dLon);
return Math.atan2(y, x).toBrng();
}
/*
* calculate destination point given start point, initial bearing
(deg) and distance (km)
* see http://williams.best.vwh.net/avform.htm#LL
*/
LatLon.prototype.destPoint = function(brng, d, meanRadius) {
var R = meanRadius; // earth's mean radius in km
var lat1 = this.lat.toRad(), lon1 = this.lon.toRad();
brng = brng.toRad();
var lat2 = Math.asin( Math.sin(lat1)*Math.cos(d/R) +
Math.cos(lat1)*Math.sin(d/R)*Math.cos(brng) );
var lon2 = lon1 + Math.atan2(Math.sin(brng)*Math.sin(d/R)*Math.cos(lat1),
Math.cos(d/R)-Math.sin(lat1)*Math.sin(lat2));
if (isNaN(lat2) || isNaN(lon2)) return null;
return new LatLon(lat2.toDeg(), lon2.toDeg());
}
/*
* construct a LatLon object: arguments in numeric degrees
*
* note all LatLong methods expect & return numeric degrees (for
lat/long & for bearings)
*/
function LatLon(lat, lon) {
this.lat = lat;
this.lon = lon;
}
/*
* represent point {lat, lon} in standard representation
*/
LatLon.prototype.toString = function() {
return this.lat.toLat() + ', ' + this.lon.toLon();
}
/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- - - - - - - - - - - - - */
// extend String object with method for parsing degrees or lat/long
values to numeric degrees
//
// this is very flexible on formats, allowing signed decimal degrees,
or deg-min-sec suffixed by
// compass direction (NSEW). A variety of separators are accepted (eg
3º 37' 09"W) or fixed-width
// format without separators (eg 0033709W). Seconds and minutes may be
omitted. (Minimal validation
// is done).
String.prototype.parseDeg = function() {
if (!isNaN(this)) return Number(this); // signed
decimal degrees without NSEW
var degLL = this.replace(/^-/,'').replace(/[NSEW]/i,''); // strip
off any sign or compass dir'n
var dms = degLL.split(/[^0-9.]+/); // split out
separate d/m/s
for (var i in dms) if (dms[i]=='') dms.splice(i,1); // remove
empty elements (see note below)
switch (dms.length) { // convert to
decimal degrees...
case 3: // interpret
3-part result as d/m/s
var deg = dms[0]/1 + dms[1]/60 + dms[2]/3600; break;
case 2: // interpret
2-part result as d/m
var deg = dms[0]/1 + dms[1]/60; break;
case 1: // decimal or
non-separated dddmmss
if (/[NS]/i.test(this)) degLL = '0' + degLL; // -
normalise N/S to 3-digit degrees
var deg = dms[0].slice(0,3)/1 + dms[0].slice(3,5)/60 +
dms[0].slice(5)/3600; break;
default: return NaN;
}
if (/^-/.test(this) || /[WS]/i.test(this)) deg = -deg; // take '-',
west and south as -ve
return deg;
}
// note: whitespace at start/end will split() into empty elements (except in IE)
/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- - - - - - - - - - - - - */
// extend Number object with methods for converting degrees/radians
Number.prototype.toRad = function() { // convert degrees to radians
return this * Math.PI / 180;
}
Number.prototype.toDeg = function() { // convert radians to degrees (signed)
return this * 180 / Math.PI;
}
Number.prototype.toBrng = function() { // convert radians to degrees
(as bearing: 0...360)
return (this.toDeg()+360) % 360;
}
/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- - - - - - - - - - - - - */
// extend Number object with methods for presenting bearings & lat/longs
Number.prototype.toDMS = function() { // convert numeric degrees to deg/min/sec
var d = Math.abs(this); // (unsigned result ready for appending
compass dir'n)
d += 1/7200; // add ½ second for rounding
var deg = Math.floor(d);
var min = Math.floor((d-deg)*60);
var sec = Math.floor((d-deg-min/60)*3600);
// add leading zeros if required
if (deg<100) deg = '0' + deg; if (deg<10) deg = '0' + deg;
if (min<10) min = '0' + min;
if (sec<10) sec = '0' + sec;
return deg + '\u00B0' + min + '\u2032' + sec + '\u2033';
}
Number.prototype.toLat = function() { // convert numeric degrees to
deg/min/sec latitude
return this.toDMS().slice(1) + (this<0 ? 'S' : 'N'); // knock off
initial '0' for lat!
}
Number.prototype.toLon = function() { // convert numeric degrees to
deg/min/sec longitude
return this.toDMS() + (this>0 ? 'E' : 'W');
}
Number.prototype.toPrecision = function(fig) { // override
toPrecision method with one which displays
if (this == 0) return 0; // trailing zeros in
place of exponential notation
var scale = Math.ceil(Math.log(this)*Math.LOG10E);
var mult = Math.pow(10, fig-scale);
return Math.round(this*mult)/mult;
}
/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- - - - - - - - - - - - - */
On 8/20/07, Erik Uzureau <erik.uzureau at metacarta.com> wrote:
> I know that there is a ticket for this in TRAC... and there may or may
> not be work underway to solve this.
>
> I know also that there are some wierd math-heavy functions in the (i
> believe) Util.js file which can be used to calculate distance between
> points.
>
> It has for a while been a (low) MetaCarta priority to add this
> functionality to OpenLayers
> erik
>
> On 8/19/07, Chris Hardin <chrislhardin at gmail.com> wrote:
> > I want to click a point and drag a line to another point on the map
> > and a measurement be given. I could write this myself, but I was
> > hoping there might already be something included or an add on I could
> > use. Does anyone have any ideas?
> > _______________________________________________
> > Users mailing list
> > Users at openlayers.org
> > http://openlayers.org/mailman/listinfo/users
> >
>
--
Chris Hardin
Software Architect
Archetype Corporation
More information about the Users
mailing list