Livecode Precision or me?

[Michael Doub]

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;
>     }