As a fact point: there is little to no problem is establishing the algorithm for giving “good” altitude gained, it is simply
that Avocet has the patent on the algorithm when they developed the Avocet 50, a number of years ago. With Avocet out
of business, nobody has really had a good altimeter with cum altitude gained.
While GPS has some problems with getting altitude changes very accurate (for instance, vertical height with WAAS is lucky to pick up 20-30 ft),
a barometric GPS (think Garmin **Edge **205, 305, or Vista) can pick up a 15 ft change nicely.) Sometimes the barometric method has its own set of
problems since it depends on a given air temperature for air density, thus very hot and very cool days can also screw you up.
A bigger problem with “flat” course is that they are not.
Most people simply cannot see low degree inclines, however, without them we’d all be facing very unpleasant pooling of water in our local
neighborhoods and lots more mosquitoes. Town are built to make sure roads slope and lead to collection sites. So, you are gaining and
losing elevation and not knowing it even on flat courses.
However, low degree inclines aren’t really going to be seen by the body either. The additional input of going up a 1 degree incline will be approximately
1.7% of your weight. Thus a 200 lb rider will feel 3.5 lbs pulling back on them. The uphills won’t slow you down (much) and the downhills don’t
speed it up (much).
Avocet recognized this, and as Jobst Brandt likes to point out, Avocet said "well we just won’t register a climb if it is less than 10M or roughly 30 ft.
Thus using the Avocet 50, you could ride that pancake flat course, which may never vary more than 20 ft up and down, and you would see
zero feet gained. The Avocet, while maybe a bit conservative, felt right to many of us old timers.
Jobst had claimed that nobody wanted to violate their patent, so nobody has this algorithm in their altimeter. Topfusion, however, allows you to
“dial in” a number from zero to “what-ever” like the old Avocet, and thus you can recreate an “on board” Avocet with their “off board” software.
See picture below for a comparison of the raw data, GPS map data, and a filter set to 10M like the Avocet.
Topofusion probably has the best assortment of ways to figure out altitude gained. The custom Algorithm is the Avocet algorithm.
So, now the question “how do I get data into TopFusion.” You want to dump your data from your Garmin into a GPX file for pre-existing
rides. If you have something like Mapsource this is a “save as” feature to save as GPX.
TopoFusion will also import most Garmin type GPS through USB/Serial directly.
Theo
