Livecode Precision or me?

Michael Doub mikedoub at gmail.com
Sat Jan 31 15:33:34 EST 2015


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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