Geocaching.com distance calculations

[+ivss_xx]

So, I found a cache very far away from my home location. It's almost antipodal, actually.

And with this find I also discovered that such a seemingly simple concept as distance between two locations is not simple at all, and that when calculating the distance between two points on Earth, the results may vary.

OK, so there's different ellipsoid models of Earth, there's different formulas to calculate the distance but which one do you think is the most 'correct' one?

 

And which one does the geocaching site use?

And why is it that the site uses two of them? The distance to that cache shows up different when I look at the cache page (20011.1) and when I look at my statistics (19997.632).

 

This is the cache I'm talking about - BASILICA SAN MARTIN DE MONDONEDO

I've also tried calculating the distance using various tools, the results vary with every one This is the summary as I've posted it in my log:

 

20011km from my home location - that is what the geocaching site says. I always trust GPSvizualizer for these calculations but it's Vincenty formula calculator gave an error - not suitable for antipodal calculations. Interesting that Geocaching statistics page gives a different distance from the cache page - 19997km.I tried calculating using different formulas and methods and here are the results:

 

20033.54km according to Garmin Oregon 700 using WGS84 map datum and spheroid

20033.10km according to Project-GC

20033.10km according to Chris Michel's calc (sphere)

20011.12km according to GSAK

20011.10km according to the cache page

20010km according to Haversine formula from MT (sphere)

20002.42km according to Google Earth

20000.22km according to NGS calculator that uses the Vincenty algorithm (ellipsoid)

19998km according to US National Hurricane Center calculator

19997.63km according to Geocaching.com statistics

 

 

P.S. I also got the FTF on that cache, could this be the longest (distance-wise) FTF run ever so far?

Edited April 15, 2017 by ivss_xx

[Moun10Bike]

I don't know the details of the methods the devs coded for determining distances. but I do know that the cache page uses a more accurate but intensive calculation than the stats page, which has to calculate many distances at once. This is why you see differences in values at extreme distances.

[+noncentric]

This thread might have helpful info. Error in distance calculation

[+hzoi]

This thread might have helpful info. Error in distance calculation

Was about to hunt it up to post same when I saw you beat me to it.

[+ivss_xx]

I don't know the details of the methods the devs coded for determining distances. but I do know that the cache page uses a more accurate but intensive calculation than the stats page, which has to calculate many distances at once. This is why you see differences in values at extreme distances.

 

Interesting to know. But I wonder now if the method on the cache page would be the most accurate of the ones I mentioned? GSAK gives almost the same result, so maybe that would be the one?