One of pleasures I get out of geocaching when I am not out in the field is the statistical side of things. Can I find a cache placed in each of the D/T combinations? Can I find a cache placed in every month since geocaching started? Can I find caches where the owners name ticks off a letter of the alphabet? The list is endless. For some time I have used GSAK to manage my caching data. It’s indispensable as I am fortunate to be able to travel and need to keep track of a wider range of data than most cachers seem to need to do.
Over the past couple of years as the geocaching.com offering has evolved and the API opened up to third parties, GSAK has also developed very quickly. Great credit is given, not only to Clyde who seems to live and breath GSAK development, but also to a number of clever and enthusiastic geocachers who have the enviable quality of being able to program. The combination is magic.
My favourite part of GSAK is undoubtedly the FindStatsGenerator macro (FSG) that has evolved into something really powerful. The possibility that now exists to add plug-ins to the macro makes it even more powerful and desirable. There are alternatives that do a great job of creating statistics of all forms and as they are predominately on-line services they require the user to upload their finds PQ and then clip in the generated HTML code to wherever they want to use it. It’s an easy way to go that suits many people. However, it isn’t my preferred way of working.
There are however, some things in the statistics that have confused me. The thing that had me scratching my head was the part of the statistical output that looked at the caches farthest to the N, S, E and W then calculated the centroid.
Anyway I recently read on the blog of another Swedish cacher Hebb that he can never get enough of statistics either! He also used the FSG plug-in FSGPlugin_MostNSEWCache and got a map that seemed completely logical to me. The centroid was where I would expect it to be.
In my case it looks completely wrong.
My eyes say that the mid point between Sweden and New Zealand is not in the Baring Sea which is only 2000 km away from home and in the “wrong” direction. So why is it there? I turned to the GSAK support forums and after a wee search I found the answer. It is logical but not easy. Here’s the Link
Basically as we are living on an elliptoid world and not a 2D one the centroid is calculated by converting the latitude/longitude coordinates into 3D cartesian coordinates and averaging them. The result is then projected back to the surface of the earth using the WSG84 model that most GPS’r use as their base.
Trust it! It works but the results take some getting used to in my case.