VRECKON: Find the endpoint of a geodesic on the ellipsoidal earth

Hello,

I am having trouble producing the correct results using this submission. Over the past few days I have been trying to code my own program similar to this one and for a test point I kept getting the wrong answer. I eventually came across your code and it also gave the same answer my code gave for the test point. I have checked Google Earth and even the website that uses a Javascript to calculate the latitude and longitude of a point given a distance, bearing, and an initial point.

To illustrate my problem I have the following initial point latitude and longitude:

39° 44′ 42.41″N
105° 00′ 5.01″W

or

39.74511389
105.0013916667

And the following distance (meters)

23.14288153 meters

And the following bearing

319°24′ 0″

or

319.4

Now when I send these values to the function you developed I get:

>> [x y] = vreckon(lat1, lon1, s, a12)

x =

          39.7452721501884

y =

          105.001215949306

Now the value I get using the Javascript from the following website (http://www.movable-type.co.uk/scripts/latlong-vincenty-direct.html) is:

39°44′42.9797″N
105°00′05.6426″W

or

39.74527214
105.0015674

As can be seen the latitude value matches well, but the longitude is far off. On that website the author even gives the code (using the same formulas you used) for the Javascript so I wasn't sure where the difference could be. Finally, I checked Google Earth and the latitude and longitude produced by the aforementioned website are the correct values. I believe the problem lies in using the "mod" function (my code uses it as well), but again I'm not sure.

Could you perhaps provide some insight into this problem? It would be of great help for my project where accuracy is a issue. Thanks.

Kevin Ellis