Hello Captain Numbers.
Let me explain a little more.
In order to calculate distance we do a great circle arc calculation based on the lat/lon of one cache to the lat/lon of another cache.
This is the forumla we use:
Code: Select all
acos(cos($lat1)*cos($lon1)*cos($lat2)*cos($lon2) +
cos($lat1)*sin($lon1)*cos($lat2)*sin($lon2) +
sin($lat1)*sin($lat2)
) * $earth_radius;
As you know (of all people), an acos (arccosine) can only be used on a value between -1 and 1 which will return a value between 0 and pi(). (I hope I got that right).
For a reason not to be explored too deeply, the calculation which is being used to determine the value input to the acos() function was showing up as 1 when I display it, but the acos() function was returning NaN. NaN is geek terminology for Not a Number.
I have a sneaking suspicion that there is a floating point error with the length on the decimals in use in the calculation so it was attempting to acos() a value that looked like 1, but was probably somewhat, only, marginally larger than 1.
So when the final acos() function was called, it failed due to the 1.000000000000000000000000000000000000000000000000000000000000000000000000000000000000001 (or some such weirdness).
So when in doubt, handle the exception. I now check for the acos() function to determine whether it has returned a valid number or NaN. If it's NaN I assume it to be 0 and the function now happily continues on its way.
In all the years of the distance calculator being used at GCA, this has never happened before, so it's a rarity (and therefore weird).
Thank you for your attention. We now return you to the non geek portion of the show.
c@w
