Author Topic: Dedicated Handheld GPSr vs SmartPhone placed caches....finder beware.  (Read 4033 times)

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bluelamb03

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As more and more Smartphone users download the app and set off for the woods there is going to be more and more caches placed by users depending on the Smartphone for accurate co-ordinates. This is a problem because of the way some smartphones 'locate' themselves.

Have a look at http://academics.skidmore.edu/blogs/onlocation/2012/03/smartphone_accuracy/ where a simple experiment found that:

Quote
When points are separated by large distances, the position provided by iPhones is accurate enough to discriminate between locations. If precision is paramount or points are close together a GPS unit is still required to get significant results.

IF the smartphone has good satellite lock it can be fairly accurate, but when the horizon is blocked by a structure or heavy canopy the phone often defaults to a coarser calculation without necessarily warning the user that accuracy has degraded. One paper I read found median errors of 8 m with GPS-assisted 3G iPhones, a median of 47 m errors for WiFi, and median errors of 600 m (!) for cellular positioning, all compared to GPS alone.

I've now had some experience with caches placed with smartphones. A series of caches placed in Massena by "iamthelevel" had the curious feature that some were spot on the co-ordinates and some were over 15 meters off! A little discussion with the cacheowner revealed that he was using the gc.com app on an Android device. The caches in the open where on the numbers, the caches in heavy cover were a problem....

What's that mean for you and your iPhone newbie? It means you have to be extra diligent in ensuring you've got good co-ordinates. You should also consider a good hint and a obvious "that's where I'd put it" type of location. There is nothing more frustrating than the cacher with 10 finds who places a 'needle-in-a-haystack' micro 15 meters off the posted co-ordinates and provides no hints.

If you're a casual cacher who wants to place some hides with your new iPhone app please do some homework first and save yourself a lot of DNF's on your cache and emails from frustrated cachers!

Blue -
Without shared stories we are strangers.
- Sheila Mendonça


GreyingJay

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One easy thing to try is to come back on a different day (or even better, multiple days with different weather conditions) and use your own iPhone or GPS to "find" your own cache using the coordinates you wrote down previously. This way you'll get a sense for where people will be led. You might be surprised.

BlackRose67

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One easy thing to try is to come back on a different day (or even better, multiple days with different weather conditions) and use your own iPhone or GPS to "find" your own cache using the coordinates you wrote down previously. This way you'll get a sense for where people will be led. You might be surprised.

I've done that, and there can be quite a bit of drift.

There have been times where I've had my Android phone in one had and the GPS in the other.
Out in the open they are close, but the difference between the two is quite surprising when a bit of tree cover is introduced.
My phone is rooted with an optimized GPS config file, and it's still a crap shoot.

Frogging101

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I use my Android phone to place caches. But to get the coordinates I use an app called GPS Averaging, which gives much more accurate results than other methods.

hidnseek

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Does it also come down to how many bars you get? I assume they go down with coverage as well.  Thus suggest if you have full bars better accuracy, if not full bars beware?


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GreyingJay

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Does it also come down to how many bars you get? I assume they go down with coverage as well.  Thus suggest if you have full bars better accuracy, if not full bars beware?

Not necessarily. The number of bars is the signal strength of the nearest cell tower, and that really has no direct bearing on the GPS satellite coverage, although the same root causes can affect both -- if you're downtown surrounded by tall buildings, then those buildings will block cell towers AND satellite reception, so both go down at the same time.

I use my iPhone regularly to geocache in areas where it has little or no cell coverage (out in Lanark for example) but the GPS is fine.

The lack of a cell signal can also mean that "assisted GPS" features are not available (where the phone can use its network connections to help figure out where it is faster, before the full GPS signal lock is finished). But if you give the phone long enough, assuming the skies are clear, it will still find itself just fine.

GreyingJay, B.Eng(C.Sys), M.A.Sc.(EE) ;)

Starkiller

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Re: Dedicated Handheld GPSr vs SmartPhone placed caches....finder beware.
« Reply #6 on: November 28, 2012, 12:43:33 »
I have done my own tests, and so far my android phone is more accurate and more reliable than my GPS. I really didn't expect that.

BlackRose67

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Re: Dedicated Handheld GPSr vs SmartPhone placed caches....finder beware.
« Reply #7 on: November 28, 2012, 12:58:54 »
What Android phone do you have? 

My first gen Galaxy S is OKish (15m - 30m accuracy) as long as I've got open sky vs a reported 3m accuracy with my GPS.

GreyingJay

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Re: Dedicated Handheld GPSr vs SmartPhone placed caches....finder beware.
« Reply #8 on: November 28, 2012, 13:21:42 »
I have done my own tests, and so far my android phone is more accurate and more reliable than my GPS. I really didn't expect that.

I have found that on a good day, my iPhone can be slightly more accurate than my GPSMAP 60csx, but if signal coverage is bad, it can swing a bit more wildly. I have also found that the official Geocaching app has numerous quirks of its own, not least of which is occasional lagging and pausing and a sometimes inaccurate bearing indicator (I don't know if that's the app, or the phone GPS or compass acting up).

Nothing more frustrating than being disoriented in a swamp, knee-deep in water, only 40 meters away from the cache, but which direction?!

After that day I really should remember to pack my regular GPS into my backpack as a backup. Just in case.

Starkiller

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Re: Dedicated Handheld GPSr vs SmartPhone placed caches....finder beware.
« Reply #9 on: November 28, 2012, 13:51:27 »
What Android phone do you have? 

My first gen Galaxy S is OKish (15m - 30m accuracy) as long as I've got open sky vs a reported 3m accuracy with my GPS.

Galaxy S3