Livecode Precision or me?
Michael Doub
mikedoub at gmail.com
Sat Jan 31 15:42:36 EST 2015
Of coarse it was me. And as you would expect, I found it right after
sending the mail to the list.
put lon2 - lon2 into dlon should be put lon2 - lon1 into dlon
Sorry for the junk mail.
-= Mike
On 1/31/15 3:33 PM, Michael Doub wrote:
> I am trying to covert the javascript that computes distance based on
> longitude and latitude from this page:
> http://andrew.hedges.name/experiments/haversine/.
>
> The sites javascript is returning 0.341 miles and 0.549 km
> Livecode is returning 0.097 miles and 0.157
>
> I have been staring at this for a while. Does anyone see my mistake
> or is there a precision issue tripping me up?
>
> Thanks
> Mike
>
>
>
> on doit
> answer __latLongDist (38.898556, -77.037852, 38.897147, -77.043934)
> end doit
>
>
> function __latLongDist t1, n1, t2, n2 , mk
> put 3961 into Rm -- mean radius of the earth (miles) at 39 degrees
> from the equator
> put 6373 into Rk -- mean radius of the earth (km) at 39 degrees
> from the equator
> put t1 * pi/180 into lat1 -- convert degrees to radians
> put n1 * pi/180 into lon1
> put t2 * pi/180 into lat2
> put n2 * pi/180 into lon2
> put lat2 - lat1 into dlat
> put lon2 - lon2 into dlon
> put (sin(dlat/2))^2 + cos(lat1) * cos(lat2) * (sin(dlon/2))^2 into aa
> put 2 * atan2( sqrt(aa), sqrt(1-aa) ) into cc
> put cc * Rm into Dm
> put cc * Rk into Dk
> return round (Dm,3), round(Dk,3)
> end __latLongDist
>
>
>
> /* main function */
> function findDistance(frm) {
> var t1, n1, t2, n2, lat1, lon1, lat2, lon2, dlat, dlon, a, c,
> dm, dk, mi, km;
>
> // get values for lat1, lon1, lat2, and lon2
> t1 = frm.lat1.value;
> n1 = frm.lon1.value;
> t2 = frm.lat2.value;
> n2 = frm.lon2.value;
>
> // convert coordinates to radians
> lat1 = deg2rad(t1);
> lon1 = deg2rad(n1);
> lat2 = deg2rad(t2);
> lon2 = deg2rad(n2);
>
> // find the differences between the coordinates
> dlat = lat2 - lat1;
> dlon = lon2 - lon1;
>
> // here's the heavy lifting
> a = Math.pow(Math.sin(dlat/2),2) + Math.cos(lat1) *
> Math.cos(lat2) * Math.pow(Math.sin(dlon/2),2);
> c = 2 * Math.atan2(Math.sqrt(a),Math.sqrt(1-a)); // great
> circle distance in radians
> dm = c * Rm; // great circle distance in miles
> dk = c * Rk; // great circle distance in km
>
> // round the results down to the nearest 1/1000
> mi = round(dm);
> km = round(dk);
>
> // display the result
> frm.mi.value = mi;
> frm.km.value = km;
> }
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