Distance reporting

[JMckie]

I went on a hike (convoluted, lots of up and down trails) today with Betty powered on the whole time.

I got three different values for the distance travelled.
QueTrip reported 9.3km
QueTracks reported 10.3 km
Birdwatch reported 11km

All of them reported the same time - 2:25 minutes.

When driving, the distances agree pretty well - quite precise in fact. I wonder what is the cause of the discrepancies when on foot.

I will repeat the hike tomorrow with Pathaway recording the track as well.

[RVRodie]

I wonder if QueTracks takes elevation changes into account in its distance calculation, since it records elevation in the track log. That could account for a longer distance in QueTracks over QueTrip.

Since none of the distance calculations are available in the API, it is difficult to know how each program is doing the calculation, and on what time interval.

[JMckie]

Birdwatch samples once per second as long as you're moving. QueTrack in default mode captures less frequently. So on a more "jagged" track, Birdwatch would be more reflective of actual distance walked. If I were to change the preferences of QueTrack to go the the highest rate, I imagine the difference between it and Birdwatch will converge.

I have no idea what QueTrip is doing to lag so far behind.

[stephanpls]

Maybe QueTrip is shorter because it smoothens the track more or less. You made a hike, I imagine it was through some woods, so satellite reception may have been bad at times. Bad sat reception can mean that your position "wanders around". QueTrip may have smoothened your track (we don't know the software exactly), and that way your distance is shorter.

Just a guess!

[apersson850]

Other Garmin units don't care about the vertical distance, so I doubt the iQue does that, when showing the distance a track covers.

[Q-Eye]

Here's my half-nickel's worth of guessing...

My guess is that with a lot of up-and-down trails, they also involved a number of "swithch backs". Rarely do steep trails go up and down in a straight line.

With less frequent sampling, you might be going in one direction on the trail at one sample time and going in the opposite direction on the trail just a few feet above the previous point, but having covered many linear feet to get there.

The two samples would show that you may have traveled three feet when in fact you walked much farther to get to a point three feet from the previous sample. More frequent sampling would show a much longer distance traveled.

[si4xp]

Originally posted by apersson850 Other Garmin units don't care about the vertical distance, so I doubt the iQue does that, when showing the distance a track covers.
I thought QueTrip reports linear distance travelled. If not, then the driven distance would not match with the car odo (assuming a fairly accurate odo) for driving on a topo with lots of ascents and descents. My car's odo and Betty match pretty close, though I have not tested them on undulating topo.

I, in fact, noted the discrepancy between the Birdwatch and the actual distance I rode on a bike trail. The map shows distance of the bike loop as 4.4 miles, whereas Birdwatch reported only 2.7 miles after I rode through the loop; quite a difference. I assumed map must be wrong. But, now I am not sure.

[Statsman]

Can anyone ride in one of those glass elevators on the outside of a building/hotel and check to see if the distance changes?:D

The Boneventure in Los Angeles would be perfect for this.

[apersson850]

It's a very common error to believe that there's a large difference in the travelled distance, if you take the slope into account, compared to a prjection on the plane.

On the contrary, for all sensible roads, the difference is neglectible. A slope of 10% is a rather steep hill, along a road. Except for in very hilly areas, such slopes are rather rare along the roads. Still, such a slope doesn't make the distance travelled very much longer. Do the math and see for yourself.

[JMckie]

On the same hike, again I got four rather different distances using four different programs.

Birdwatch Trip - 10.01km, 2:07:44
QueTracks - 9.68km, 2:07:33 (351 track pts)
QueTrip - 9.39km, 2:07
Pathaway - 8.65km, 2:07 (108 track pts)

After some analysis, I figured out that it must be due to the difference in how often the position data is sampled. A picture can explain it a lot faster (see attached file).

These are the different sampling frequencies:
Birdwatch - once every second
QueTracks - every 21.7 seconds (track frequency set to highest setting)
QueTrip - guess: every 30 seconds?
PathAway - every 70 seconds

When on foot, you can travel several meters in 30 seconds, and these add up as you can see. Of course with straight trails, the effect is negligible. This is also why the distance numbers are pretty much the same when driving.

Different GPS receivers will report different hiking distances depending on which sampling frequency is used. I wonder if there is a standard for this. On trails, you see distance markers. How do they arrive at these distances?

[Bee_sqare]

One (common?) way that trail distances are measured is with a distance-measuring wheel that rolls along the trail and includes a digital odometer. So the distance measured is (a good approximation to) the actual length of the curve that the path traces out through space (as opposed to a piecewise-linear 2-dimensional projection of this curve on a plane or sphere, as might be measured by a GPS).

[apersson850]

With my (rather) old eTrex Vista, I've noticed another interesting effect.
If I set it to display the Swedish topo maps, then these maps are so badly designed, that they require more CPU power to display than the Vista can provide. Thus, as soon as I start moving, if I have the map set to track up, the Vista will start considering to refresh the map image on the screen. But that takes so much of the available capacity, that even at 10 km/h, the map will never be ready to display, before your movement has made the new image obsolete.
Thus it redraws the map (internally), come up with an image that's once again obsolete and so on. This goes on forever, or at least until you stop.
Meanwhile, your position (the black triangle) is shown on the map, but it will eventually move off the screen, if your progress takes you off the map, as it's currently shown.
During this intense preparations to update the map image, sampling of the track, as well as updates to the trip distance, aren't performed normally. Thus the track is cut off, and the reported distance is often the straight line from where you started moving, with these maps enabled.

Mapbe there's something similar here.
If not, it's probably Joseph's idea about a trip distance filter, that cuts out the finer details of your trip.

[si4xp]

Originally posted by JMckie
Birdwatch Trip - 10.01km, 2:07:44
QueTracks - 9.68km, 2:07:33 (351 track pts)
QueTrip - 9.39km, 2:07
Pathaway - 8.65km, 2:07 (108 track pts)
I chaned QueMap/Preference/Tracks settings to "Most Often" for sampling thinking this should also change the QueTrip sampling? However, QueTrip did underreport the distance vis-a-vis the QueTrack for the bike trail that I rode through yesterday. This means, QueTrip has a mind of its own. Strange, considering both programs are by Garmin and they don't agree with each other!:confused:

[si4xp]

Joseph,
I use a iQue handlebar mount to monitor progress while mountain biking. Since, doing my test yesteday, when QueTrip underreported QueTrack, and Birdwatch, I decided to go back to Birdwatch. And here is my request: Could you make the fonts of Stopped and Moving times as big as the Odo? This would make reading off the numbers much easier while biking. Since I use bike for fun and for workout, the numbers I monitor are:
1. Odo & Moving Time - for distance and duration of workout
2. Speed, and Heart Rate* for intensity of workout
3. Time
* (using a HR Monitor)

[JMckie]

I wish there was a way to configure QueTrip. As it stands, the odometer very well in driving scenarios, but will under-report hiking or bicycling distances.

One interesting thing to try next time is to compare the different distance values with the trail markers, if available.

By the way in Pathaway, there are several options to choose the interval for recording tracks. By default mine was set to every minute although you could increase this to once per second. This would increase the size of the track log though. The Birdwatch tripmeter (or tracklog), which logs once per second will not increase in size no matter how long your trip is.

si4xp, regarding the numbers, why don't use use the Trip export button and Trip reset button? That way you can save all pertinent details for each leg in a memo. You can open this up in Excel later on.

[si4xp]

Originally posted by JMckie
si4xp, regarding the numbers, why don't use use the Trip export button and Trip reset button? That way you can save all pertinent details for each leg in a memo. You can open this up in Excel later on.
Joseph,
My request was for monitoring these numbers while biking, and not afterwards. The only reason, I was using was QueTrip was the font sizes for moving and stopped times, which though not as big as I wanted, were at least a little bigger. But, now I have decided to switch back to Birdwatch because not only it is more accurate in distance measurement, it also shows time, which QueTrip doesn't.

You might like to add this request to wish list for the next Birdwatch upgrade, if any.:)