Hamilton Creek, Take Two

Today, I rode the rest of Hamilton Creek East. The southern section did have more spots where I could flow though the trail with some speed. But it also presented a set of downhill rock moguls and a few sharp, rocky ascents that were a little above my skill level. I was happy with the way I ground out some of the climbs and handled most of the downhill though.

I also ran an experiment with my iPhone and my Garmin 60CSx and was disappointed with the results. The iPhone reported a 3.5 mile trip whereas the Garmin indicated I'd ridden 4.5 miles. Not sure how to account for the one-mile discrepancy yet, but I'm going to send in a query to the good folks at Everytrail and see if I can get some answers.

On the iPhone, I am running an application provided by Everytrail, and one thing I notice is that the iPhone trail data is a lot smoother. I wonder if this blunting of angles is a function of the software that Everytrail uses for the iPhone.

Hamilton Creek iPhone at EveryTrail

Map created by EveryTrail: Share GPS Tracks

The Garmin trail data, on the other hand, looks more angular. It also appears that more trail is recorded and that the angles gradually build up more mileage over the course of the trip.

Hamilton Creek Garmin 60CSx at EveryTrail

Map created by EveryTrail: Share GPS Tracks

I also created a new "trip" in Everytrail and overlaid the two versions. Below is what the amalgamation looks like. The two tracks are similar, but there are lots of small inconsistencies throughout. Regardless of smooth versus angular, my main concern is that I get a relatively accurate mileage report. Once I hear back from the Everytrail people, I will post an update here.

Hamilton Creek Combined at EveryTrail

Map created by EveryTrail: GPS Community


UPDATE:

Certainly, part of the reason for the discrepancy involved the settings. The iPhone was set to sample waypoints every 10m with 10m accuracy. The Garmin, on the other hand, was simply set to "Auto," which I'm told involves recording waypoints when the device recognizes a directional change. That scenario would help explain the more jagged lines and angular shape of the Garmin trail. I'll continue to work on the Garmin settings and experiment more with time sampling and distance sampling.

Another reason for the difference is likely the inherent inaccuracy of GPS data. One mountain bike rider told me that he regularly rides and tracks the same trail, and his distances vary between 25 and 30 miles, depending on the day. Canopy can affect signal, and mountain biking is usually done under a lot of trees.