The iPhone as a GPS and a Possible Alternative

[kforte318]

I was just curious as to what everyone thought about using the iPhone as a GPS. I have been geocaching with it for almost a year now, and I've realized that, whenever a cache is deep in the woods, I can't seem to find it. This has happened with 4 or 5 caches, and I was pretty discouraged, assuming that I was just terrible at hunting (although I did just fine with caches in more open areas). A few days ago though, I was looking for a cache Right along a lake shore in a pretty heavily wooded area. To my surprise, when I was at the edge of the lake, my phone was telling me to proceed forward another 87'. My phone was 87' off in a partially wooded area, no wonder I wasn't finding anything! I was just curious if anyone else was experiencing similar problems?

 

Also, what would you suggest as the best alternative on a budget? I geocache quite a bit now and figure it's time for some new equipment.

[tr_s]

87 feet doesn't sound too far off, dedicated GPS receiver or not. Yesterday I was in the woods with my eTrex 30 along a path. Following the same path out tracked more than 40 feet off the track that was drawn by the receiver just two hours before that.

 

Consider also a double effect. The cache creator might have bad reception upon recording the coordinates.

 

The idea is not that the navigator shall take you spot onto the cache, just to the general vicinity, then you have to search and read hints.

 

I think the gps chipsets in smartphones are just about as good as any other modern GPS receiver as long as there is a satellite lock as I haven't seen much evidence for the opposite.

[tr_s]

 

With WAAS, accuracy apparently improves to less than 3m 95% of the time, but I've found no significant difference using WAAS so I keep it switched off. Even then since getting my Etrex 20 some 8 months ago now I've found that it's accurate to well within 3m, and in most cases within a few feet

 

I've found that glonass actually DOES improve accuracy under heavy tree cover (if we discount the sticky error). If there is a good view of the sky it worsens it, but not by much.

[tr_s]

I agree that GLONASS improves accuracy ... that's why I run mine with GPS and GLONASS on but with WAAS off

 

Are you sure you are actually getting a WAAS lock (see D on the signal bars?) It is supposed to give a good reduction of systemic position error, as most of the variable atmospheric effects are cancelled out. EGNOS is almost unusable in Sweden for anything but open-water naval and air use (which are the only situations in which I can get a lock), as the geostationary satellite AOR E is so low down on the horizon any foliage or obstructions will kill it. If you are from the UK, especially northern, wouldn't surprise me if it isn't much better there.

[tr_s]

That's certainly true and is another reason why I run with WAAS/EGNOS off, and probably why you and I benefit from GLONASS, which as I understand it has a more significant effect at more Northern latitudes.

 

However last year when I decided to do some what were, to me, pretty exhaustive tests I was in the Isle of Wight for a week, an island off the South coast of the UK and with clear views to the Southern horizon. This convinced me that WAAS/EGNOS made no discernible difference in the real world, no matter what the 'accuracy' figure of my GPS was telling me

 

Interesting, over the next few days I'll run some stationarity tests on GPS and GPS+WAAS, we'll see what results I get. I'll possibly throw in some glonass testing as well.

Edited May 16, 2012 by tr_s

[+user13371]

Sussamnb and TR_S, it's a waste of time to look at the the GPS "accuracy" figure on screen - once or a dozen times - to decide if WAAS or GLONASS are actually useful.

 

Here's a minimal description of the only testing that can be meaningful: Set a waypoint on a known location you can get back to. And do it again lots and lots of times over a period of many days. Then graph the points. The smaller the scatter plot, the better.

 

The problem is, you gotta repeat that LOTS of times, with various the various features you want to test ON or OFF, to collect enough data. A single user testing a single GPS is going to need a lot of patience and a lot of time to do that properly.