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Discussion: GPS track....

in: Jagge; Jagge > 2010-06-09

Jun 9, 2010 3:59 PM # 
Jagge, what gps unit do you use.Your data track is perfect. The tracking is so precise. I could never get the same precision and consistency from the Garmin units.

Ahh, nice run by the way :)
Jun 9, 2010 4:10 PM # 
I bought Holux m-1200e last winter and been using it for orienteering and running this season. It is usually pretty accurate if there is no three shadow and if held like I do, on top of my sholder (or on head / cap). It's tiny unit (30g) and it has quite small antenna, so accuracy isn't that good if there is body shadow or forest. If you browse my log you'll find several forerunner vs. holux comparisons. I believe fore (sirf III with good antenna) is more accurate than this unit, but it is true if there is no trees or anything this little thing is pretty accurate, maybe more accurate then fore. Possibly because it seems to usually use more (1..2) satellites than sirf units to calculate position.

I bought it from dealextreme, $53.

Conditions were good and I gave my best shot.
Jun 9, 2010 7:03 PM # 
Well, see Ross's log from the 5K TT. My logs look similar. The split points are all over the start finish line, and the tracks themselves are not nowhere near as nice and tight.
I am thinking now, that maybe the hand swinging while running is messing up the Forerunner smooting and error correction, and your logger is moving steady when on your head or shoulder.
Jun 9, 2010 7:34 PM # 
Note, I did not take splits manually. I just hand picked points nearest to the start line. Thats why they are so nicely close together. But timing may not be as accurate.

There is tall building close the track Ross were running. That may have had some effect. But I must admit my logger is usually very accurate in open terrain. The problem is orienteering is done in forest and there my forerunner (and globalsat unit) is better.

What it comes to forerunner and hand swinging, I dount think the swinging is the problem. More likely it is the fact your body shadow is blocking different satellites depending on what part of the track you are running. For example you are runinng 180 degrees other direction on straights, so your body is blocking satellites at opposite sides. Thats why device end up using different satellites for position calculations. And that means the error may be to opposite direction, so gps end up drifting out and back all over again. If held on head the device will see same satellites all the time, so it will end up drifting a lot less. On shoulder there is head's shadow but that may not effect that much. And in open terrain holux's chipset is not as sensitive to that problem, like I said it keeps using all possible satellites longer than sirf III (even if it sometimes should not). Holux has the same problem (but worse) in forest.

take a look at this:

West part of the east X. It looks like I would have used two paths, on for running out and an other for coming back. Both have same effect, but Fore is better. I thnk this is because I turn around 180 degrees and my body shadows different satellites. But I haven't confirmed this with cap gps setup.

Note also, holux's tracks are close together on the open hilltop, Fore is not. Usually Holux is very accurete in open land, like now on track. It looks like Forerunner is almost as accurate in forest than in open terrain.
Jun 10, 2010 4:01 AM # 
Yes, I see that. I guess its a combination of factors.
I'll have to put my forerunner on my cap next track session :) And see if there is any difference.
Jun 10, 2010 4:28 AM # 
Andzs has beed carrying gps units on his head for quite some time. He has got some impressive results with it and might be able to tell the difference.
Jun 13, 2010 4:20 PM # 
During summer time I'm not carrying GPS unit on head anymore. No cap on head you see ;) I sacrifice precision and carry it in holder on arm. Thats probably worse than wearing on shoulder but I have not figured out nice method how to do that. From my experience I would say that placement of GPS unit matters. GPS track is more consistent.

This discussion thread is closed.