SPOT 3 vs Garmin Mini Live Testing

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CAMERONM
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SPOT 3 vs Garmin Mini Live Testing

Post by CAMERONM » Fri Jun 15, 2018 10:58 pm

I just received my new Garmin MINI and am going to test it out starting June 17 for a few days in the Thousand Lakes area. I include links to the SPOT and MINI share pages so that if anyone is interested they can view my tracks in real time, comparing how both devices present information and the accuracy of the tracks. I will also post a report about my conclusions after the trip. Nothing will appear on these pages until I activate tracking sometime Sunday morning.
MINI:
EDITED: I REMOVED THE MAPSHARE LINK AS I LEARNED THAT IT DOES NOT CUSTOMIZE SHARE OPTIONS. SORRY. THE CALTOPO LINK THAT FOLLOWS IS NOW MORE VALUABLE ANYWAY.
SPOT:
http://share.findmespot.com/shared/face ... B5yW1z9FXr
Last edited by CAMERONM on Wed Jun 27, 2018 4:13 pm, edited 1 time in total.








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bobby49
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Re: SPOT 3 vs Garmin Mini Live Testing

Post by bobby49 » Fri Jun 15, 2018 11:22 pm

Each of those devices has a GPS receiver inside. This may be a fine distinction, but most GPS manufacturers do not recommend for two receivers to be used within 18 inches of one another. That is because one may cause RF interference to the other. So, if you use two devices side-by-side, you probably want to keep them separated by somewhat more distance than that. Why not pick a nice round number like 5 feet?

When you see what a teeny, tiny RF signal is coming down from space, even the slightest amount of interference might cause an issue.

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CAMERONM
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Re: SPOT 3 vs Garmin Mini Live Testing

Post by CAMERONM » Sat Jun 16, 2018 7:54 am

Thanks for the tip! I'll be with my family, so distance between devices is easily accomplished, perhaps even desirable :)

I wonder if my extensive use of GAIA GPS tracking has interfered with my SPOT? I would carry the SPOT at the top of my pack, and iphone in my pocket. Probably a 30" distance. My GAIA tracks are superb. SPOT- not so great.

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longri
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Re: SPOT 3 vs Garmin Mini Live Testing

Post by longri » Sat Jun 16, 2018 8:49 am

I was wondering the same thing about the GPS in smart phones. Most people have a phone along too. The Garmin devices are designed to pair with a phone. So maybe it's something that can happen but isn't likely to be a problem?

I just put my phone with the Gaia app open right up next to a GlobalTop GPS. It didn't have any apparent effect.

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Re: SPOT 3 vs Garmin Mini Live Testing

Post by longri » Sat Jun 16, 2018 8:55 am

CAMERONM wrote:...my extensive use of GAIA GPS tracking...
Off topic, do you have any sense as to the accuracy of the total elevation gain that Gaia reports?

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Re: SPOT 3 vs Garmin Mini Live Testing

Post by CAMERONM » Sat Jun 16, 2018 10:29 am

Well not so quite off-topic, as reliability of tracks is one of the aspects I am studying. I hope to transition from track-making on the iphone to the MINI so I won't burn up so much battery every day. I'll compare, and post, all three tracks. The XY on GAIA is always super close, don't know about the Z.

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Re: SPOT 3 vs Garmin Mini Live Testing

Post by longri » Sat Jun 16, 2018 12:49 pm

Okay, thanks. I've been tracking some local dayhikes with Gaia and comparing the results to another GPS app (on the same phone at the same time using what I believe are the same open source maps) and also to a barometric altimeter with an accumulator function. The three sometimes match up reasonably well but other times disagree by quite a bit. It seems almost random.

How well the GPS is working on a particular day also seems to have an effect. The same hike on a different day will result in different gain/loss and also distance. I'm talking about 2-3% variation. I can actually see the difference on the tracks, with more zigzag deviations from the route as compared to the same trail on a different day.

Example of tracks in Gaia from two different days:

Image


Of course your test is about a lot more than GPS function. It will be interesting and fun to watch, whether or not it actually proves anything. Thanks for making it public.

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bobby49
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Re: SPOT 3 vs Garmin Mini Live Testing

Post by bobby49 » Sat Jun 16, 2018 6:37 pm

With a GPS receiver, you have horizontal accuracy and you have vertical accuracy. Normally, the very best that vertical error will be is 1.5 times the horizontal error. However, if you have a poor view of the sky and poor satellite geometry, then the vertical error can be way the hell out, or maybe no vertical position reported at all. Lots of people carry their GPS receiver around at chest level so that they can watch the display. What they do not realize is that your head hanging in that part of the sky view might really foul up the view of the sky. This is very common when the user walks one way on a trail and gets one track (like the blue track on the map above) and then walks the other way (like the red track). I realize that this is inconvenient, but if you hold the receiver out from your chest at arm's length, then your head is no longer blocking such a critical view of the sky. You can get a better feel for this if your GPS receiver has a display of EPE (Estimated Position Error).

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longri
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Re: SPOT 3 vs Garmin Mini Live Testing

Post by longri » Sat Jun 16, 2018 9:45 pm

bobby49 wrote:This is very common when the user walks one way on a trail and gets one track (like the blue track on the map above) and then walks the other way (like the red track).
Weird that you would assume that. In fact both tracks were made walking the same direction, just on different days, with the GPS carried identically in both cases. And both apps determined the elevation from the map data, not the altitude calculated by the GPS.

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Re: SPOT 3 vs Garmin Mini Live Testing

Post by edhyatt » Sat Jun 16, 2018 11:20 pm

I'll be following this with interest.

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