Smart Phone GPS - should I trust it for

I’ve been using the GPS on my Android phone (HTC Inspire) to record distance paddled & speeds.

Last week while in Northern, CA I did a day paddle over 7 hours with rest stops, lunch, and fishing. Part of the paddle included several loops through an eddy.

When I ended my trip the GPS said I had paddled 19.2 miles. I estimated the trip would be 14 miles at most by eyeballing it. If I really paddled almost 20 miles then I must be doing something right, as I am not paddling miles every week as part of my training, I was not exhausted or fatigued. I suspect the GPS is WAY off. Or maybe it was my spiffy new hat?

Should I trust the phone GPS at all, or get a dedicated device?

The track, without the splits, on Google maps is here:

The 9.65 mph max speed was probably me paddling down the rapids.

Max speed probably off

– Last Updated: Aug-14-12 10:06 PM EST –

Overall distance probably fairly close since
you paddled with some current pushing
you along the way.

Max speeds are highly suspect as gps will "ping"
a satellite and it interpolates what happens between
the ping points.

if anything, distance shown can be a bit too small if it thinks you “cut corners” on your route. Only average speed means anything. Instant and max can be way off

Droid Razr
I have heard that a dedicated GPS won’t necessarily be better. I have Backpacker Light on my Razr and my wife did get me a new Garmin for father’s day but I have to admit I haven’t used the latter yet.

My best guess is that my Razr/Backpacker combo over estimates distance by about 10%, at least while hiking in hilly terrain. Since it’s keeping track of real time the speed would also be high. Other people I run into on the trail also mention the 10% number.

My neighbor claims water mileage would be more accurate since the lakes are in more open areas and you won’t have the elevation changes throwing things off.

I think it’s time I take my Garmin out and compare.

sort of
It really depends how MyTracks calculates the distance.

GPS coordinates as recorded by a simple GPS receiver are intrinsically noisy, care must be taken not to use unfiltered data for calculation of statistics and distances.

How noisy? - take a look here

If I were curious, I would look at forums of folks who really care about such things and have ability to track their mileages - think avid mountain bikers. Why mountain bikers - their tracks would be more similar to kayak tracks in terms of coverage and change of direction. Furthermore they are likely to have biking computers for double checking.

Cell Phones

Looks like this might be a lot of opinion and not totally related to OP but informative none the less.

What it measures
GPS is good with location and time, but not as good with instantaneous velocity. Let’s say you are moving 5 feet per second and your GPS takes measurements every second with an uncertainty of about 2 feet.

Assuming you move in a straight line moving east, your x position should read: 0, 5, 10, 15, 20, 25, etc – exactly 5 feet between each time step as you would expect, but when I add in some error, you might get:

0, 6, 8, 17, 21, 25, etc.

Over a long set of measurements, the average velocity is still good, you went 25 feet in 5 seconds, so exactly 5 feet per second, but the individual steps are not meaningful. The jump from 8 to 17 would make you think that you were going 9 feet per second – almost double what you really were moving.

If you average out the measurements while you were going through a fast spot, that can also be maningful, but at low speeds, the inherent error in the GPS is just too large to make max speed meaningful.


Use a GPS
I have an android phone as well (Galaxy Nexus). Despite it having a GPS and maps on it, I’d rather use my GPS. First, it’s waterproof and it floats. I can track anything I want to with the GPS and upload the tracks and info as well.

I’d hate to see my phone get wet or dropped into the water.

My GPS is a Garmin Map 76.

Thanks, all. Good feedback.
I will invest in a real GPS next season.

I will also do some tests on the mytracks setup. That last trip was set for 5 second intervals with 16’ distance intervals and GPS accuracy set to 656 ft. I’ll see if loosening and tightening those parameters helps with accuracy.

Phones “may” surpass GPS units

– Last Updated: Aug-15-12 12:58 PM EST –

According to the pundits the gps chips in phones
are approaching the stand-alone handheld gps units.

Advertisers want to do hyperlocal targeting.
If you are in front of a mall, you'll get sale info.
Tech follows the money and it's coming fast.

Water Sports folk are streaming music, weather, etc.
and the GPS app is very, very close on the heels.