Jan 14, 2013 at 2:10 pm #1298004
Have become increasingly interested in the idea of using GPS to back up my map and compass (and guesswork) when navigating off trail. Have GAIA GPS on my iPhone 4s and love it.
Is there any reason (theoretical, anecdotal, or empirical) to think that a Garmin Etrex 30 would get better GPS reception than the iPhone? Garmin is purpose built after all.
For the purposes of this thread, let's leave out any comparison of battery life, durability, or interface, and just focus on the device's ability to reliably locate you with GPS signal.
Thanks!Jan 14, 2013 at 3:15 pm #1943785
First of all, I have to admit that I've been a GPS user and instructor since 1995.
In the early days, say up until around 1997, most consumer-type GPS receivers had external (movable) antenna components of the quadrifilar design. Those were helpful in attaining necessary antenna gain and in minimizing multipath interference problems. At the same time, a few GPS receivers came out with what we know call a patch antenna, and the patch could not compare in performance. Over the ensuing ten years or so, Selective Availability was turned off, software and hardware improvements have advanced to where the quadrifilar antenna gain is unnecessary, and only in a multipath situation does it pay off. So, if you are in a multipath situation such as a deep urban environment or a concrete canyon, the quality antenna may pay off. One small additional problem happens if you are in the near field of a microwave radio transmitter.
Unfortunately, out in a wilderness, you are not going to run into many smooth and reflective surfaces, and you typically do not climb up a microwave radio transmitter tower. Therefore, the quality antenna can help sometimes, and it sure isn't going to hurt at all except for the additional small weight and the additional small power consumption.
I have to ask this. For those of you who use a smart phone with GPS feature, do you really know exactly where the GPS antenna is and how it is oriented? If you don't know where it is or how it is oriented, you may be shadowing it with your body when you look at it, and that may reduce accuracy.
I own three different Garmin receivers. This may amaze some, but when I am heading into some area where navigation is a very serious matter, I carry the oldest receiver with an external antenna plugged in. The antenna is placed between my inner hat and my outer hat (pointed upward). In that fashion, it is almost impossible to shadow the antenna and have a problem.
If you put a gun to my head and forced me to decide, I would go with a Garmin receiver.
–B.G.–Jan 14, 2013 at 3:50 pm #1943803
I've done side-by-side tests with my iPhone 4 and my Etrex 20. Ruling out all of the important to have features that you mention like durability, waterproof, battery life etc., I found the following:
In fairly open areas (few trees or canyons), as long as the iphone was held facing skyward, it was very close to the Etrex 20 in it's track and waypoint recording.
In heavily treed areas with steep terrain it didn't do as well with satellite locks.
I also found that the Etrex is less particular about "facing skyward" (I can just toss the Etrex into my pack and it just keeps tracking).Jan 14, 2013 at 7:31 pm #1943889
Mike, thanks, super useful. Should have mentioned that I don't primarily use the tracking function, more just double checking location. Would that change your assessment in any way?
Bob, you piqued my curiosity. Seems like the iPhone 4S antenna is in the external metal band on the left side (as you look down at the screen) of the phone. How would that/not impact shadowing? Also, found this about the GPS sensor in the 4S, any assistance decoding it, and in particular, comparing it to what might be in a Garmin or single purpose GPS would be awesome:
"MDM6610 inside the 4S inherits the same Qualcomm GNSS (Global Navigation Satellite System) Gen8 support, namely GPS and its Russian equivalent, GLONASS. The two can be used in conjunction at the same time and deliver a more reliable 3D fix onboad MDM6610, which is what the 4S does indeed appear to be using. GPS and GLONASS are functionally very similar, and combined support for GPS and GLONASS at the same time is something most modern receivers do now. There are even receivers which support the EU’s standard, Galileo, though it isn’t completed yet. This time around, Apple is being direct about its inclusion of GLONASS. The GPS inside MDM6610 fully supports standalone mode, and assisted mode from UMTS, GSM, OMA, and gpsOneXTRA."Jan 14, 2013 at 7:44 pm #1943894
One more technical nugget, this from a considerably less reliable source:
"what the iPhone does NOT have is WAAS capability. The GPS receiver works by measuring how long it takes for the radio signals to propagate between the satellites and the receiver. The propagation time varies based on the current density of the atmosphere between each satellite and the receiver. Because of the density flucuations, a standard GPS receiver can only get a fix that is accurate to about 10 meters. However, some geostationary satellites transmit atmospheric density information that lets GPS receivers compensate for current atmospheric conditions, and this enables accuracies in the neighborhood of about 1 meter. Garmin has had WAAS capable receivers for years, as have other hand-held and aviation-based GPS receivers, so it is a bit surprising that Apple has not incorporated WAAS into their GPS radio — especially since WAAS density data can be downloaded via the Internet, eliminating the need for increased radio weight. I and others have submitted requests for a WAAS capable GPS receiver in the iPhone, but Apple has not delivered. Perhaps it is because WAAS is only available in North America. However, according to the specs for the iPhone 4S and 5, it now supports GLONASS, which provides near-WAAS accuracy when combined with standard GPS, and is available worldwide. At least that is the next best thing to WAAS."Jan 14, 2013 at 8:02 pm #1943902
From what I've read from various reviewers and forums, the iPhone 4S has a better receiver than my iPhone 4. How much better would be nice to know. Apparently tracks were a little cleaner.
As far as tracks vs way points in my testing, it doesn't really matter. Both are a problem because the iPhone will occasionally drop it's satellite lock and then it will search for a bit to recover. Your phone has the new receiver so maybe it will do better than mine in this regard but I'd test it under heavy tree cover if I were you.
The GLONASS constellation is the Russian satellite network that in theory, will allow you to improve your accuracy because you can use both the GPS and GLONASS satellites to maintain your fix. The Etrex uses both but I find that in my area using both makes my unit less accurate so I shut off GLONASS.
Using WAAS (in my area) is not much better or perhaps worse than when it is shut off. WAAS is very much a local adjustment, so whether or not you benefit from it is dependent on where you are in the adjustment area (if one exists). You also don't need to be that accurate anyway… 10m is fine when hiking.
The GPS antenna on the iPhone is on one side (left side) which is why I find it tracks poorly when dropped in a pack or in my pocket. The Etrex seems to be less affected by this and holding it in the perfect position is less critical.Jan 14, 2013 at 8:21 pm #1943908
@aerikssonLocale: Austin, TX
I've been looking into the idea of using a Bluetooth Garmin GLO receiver for better accuracy and changeable batteries. Has anyone played with one of these? In theory just set the phone to everything off excluding Bluetooth, tether, and use Gaia Maps as usual. Moreover, you could theoretically use an iPad mini with its larger screen as a better navigational aid even if you, like I, only have the wifi only model. Thoughts? No idea on weights but that's pointless unless it even works.Jan 14, 2013 at 8:27 pm #1943911
I am curious how the iphone GPS works, and whether it is aided by the cell network when it is available. Sitting on my desk, the iphone 5 resolves my almost perfect location in a few seconds, putting a dot over my house near the room I am in. It drifts very little as it sits there, but it does drift a bit.
My garmin vista HCX took forever to acquire my location, but that was because it had been off since the summer. My old GPS could not get a reading inside, but the high sensitivity receiver on the hcx usually does pretty well. The Garmin comes pretty close too, right on the house, but then I can watch it drift around back and forth across the street as GPS do.
This seems consistent with using the iphone on the road, it acquires the location very quickly, much faster than a handheld GPS. I will most likely bring the iphone into the backcountry as a phone, but I am not sure I would think of it as a replacement for a GPS when I need a GPS. But that is all pretty much about battery life and waterproof and toughness.
edited to say: my iphone was already "on" so it had already acquired my location in my house and when I am on the road. So to really test this, I would need to turn off and move it to a new location. So that makes it appear deceptively effective in its mapping applications.Jan 14, 2013 at 8:34 pm #1943914Jan 14, 2013 at 8:55 pm #1943917
@aerikssonLocale: Austin, TX
@ken: I can speak for myself on this when I say, yes, that is a great resource and was in fact the thing I familiarized myself with before using my iPhone in the wild. Great resource. Perhaps the OP like myself is looking for additional information? Also, since the time of that original article being written, the iPhone 5 has been released with who knows what inside. It would be interesting to see who has been fiddling with these solutions besides myself. I haven't had great results with my iPhone 4 but haven't tried my girlfriend's 4S.
I'm currently lusting after the iPhone 5 however, with a Lifeproof totally waterproof case as the one device to rule them all. For the price of an eTrax (sans maps) you can possibly have a very close approximation. How close, I believe, is the point of this thread.Jan 14, 2013 at 9:34 pm #1943926
Gee, you guys are just full of good questions. How come none of you ever sat in my class? Let me try to hit some of the salient points.
I've never seen an iPhone 4S, so I have no idea about the external metal band on the left side. If metal gets in the way of the antenna, it could be a real problem. But, we don't really know where the actual antenna is.
Think about the normal way that you are holding a GPS receiver or a smart phone when you are looking at the screen. Think about where your head is, or if it is shadowing the antenna. As a general rule, your head is blocking at least some of the view of the sky toward the horizon, but that should have relatively little effect when it is within 10 degrees of the horizon (because satellite signals are routinely masked when they get below 10 degrees). If the device is almost horizontal, and your head and shoulders are directly above the antenna, then you are probably causing a problem, either small or moderate. Most devices can get a fairly decent accuracy just by looking at the remaining satellite signals.
"MDM6610"? I have no idea what that is.
GPS+Glonass support. That is an interesting question. The U.S. put up its GPS satellite system first. The Russians followed with Glonass. For some serious periods of time, the Russians could not afford proper maintenance on its system, so accuracy was seriously affected. At the last that I heard, they had pulled it together again. So, if you listen to one group of people, GPS+Glonass is superior. If you listen to another group of people, that is all marketing hogwash. I've done talks alongside some of the biggest GPS experts in the U.S., and they will tell you that it is _mostly_ hogwash and you don't need Glonass for anything unless your first name is Ivan. Theoretically, the U.S. can drop the ball and the Russians can keep their Glonass cooking, or vice versa. Personally, I have my own views. Galileo is one other system that I am not putting my money on.
WAAS was kind of another big buzzword a few years ago. Yes, it does help a tiny bit in accuracy. Is it worth the trouble? I don't know. I do not currently use any WAAS-enabled receiver, although I have had my hands on a few dozen. One problem here is that most normal receivers and WAAS-enabled receivers have other small accuracy errors going on, so whether you get 1-meter or 10-meter accuracy from WAAS is kind of a moot point. One group of people is striving for the 1-meter accuracy, because then they can use it as a primary navigation system for human-less driven cars. That is getting way outside the bounds of what a backpacker needs to find his way along the trail and out of the woods, in my opinion.
If an iPhone drops its satellite lock, that could mean any of a dozen things. I've traveled back and forth several times across the U.S. when somebody complained of just such a problem. It could be a problem in that one phone device, something about the way the user is holding it, multipath interference, antenna shadowing, or high power interference from a microwave source. Been there. Done that.
Cleanliness of tracks. That is generally a software issue. Look up Kalman Filtering. Also, the more that you shadow the antenna, the worse this problem becomes.
Some smart phones use cellular augmentation to GPS. Generally, they pick up terrestrial cell tower signals slightly before they have a GPS satellite signal lock. That is kind of a temporary thing, in my opinion. Besides, most backpackers are so far out in the boonies that there is no cell tower signal.
If a Garmin Vista HCX takes forever to acquire your location, I could believe that. Most GPS receivers have a Time To First Fix (hot), Time To First Fix (warm), and Time To First Fix (cold). TTFF cold can be lengthy, and it depends on how much of the satellite ephemeris data is still in memory and how old the data is. So, before you go off into the woods, as you are getting your backpack out of the car, first turn on your GPS receiver and place it in a place with good view of the sky, such as on the hood of your car. Leave it running there for some minutes, up to 15, and I can guarantee that it will work better than if you just wait until you are out in the woods and you start it up. Some receivers get a bad component that holds that data intact in memory, so they have to wait until long after start up before they show good results. If you are deep in the woods and moving when you try a cold start up, you will run into what we call the picket fence problem, and your accuracy may be poor for a while. If you have the device deep within a car (underneath the metal roof), then you aren't making it easy for accuracy.
If you want to see something really cool, get yourself a Mil-Spec GPS receiver with the crypto key installed. Bring along your security clearance for that.
–B.G.–Jan 14, 2013 at 11:03 pm #1943935
Bob mentions GPS software and it's a big piece of the puzzle. It's one of the concerns I have about using smart phones as navigation tools in the back-country.
The chip technology is very good these days but we are at the mercy of the software programmers because they decide what to do with the signals they receive before they present it to you. A case in point is that most car GPS's will keep your vehicle location "locked" on the road however we all know that as GPS accuracy varies, you should see your car drift off the road from time to time when the signal is weak. I see this in hand held (trail) GPS's all the time. But who would want a car nav system that put your car on top of the buildings? Not me… thank you software developers!
So the question is, what was the iPhone designed for? I say for walking in town and driving… which makes me question what is really happening inside the device. We also know that collecting GPS signals burns up a lot of battery power, so the software developer has to find a balance between too fine grained signal capture (wasted batteries) and not enough to keep you on track. Hand held GPS's generally let you set that interval but my iPhone doesn't (actually, my MotionX GPS app does but it's unclear what it's doing). So are they capturing enough points in the back-country to keep on track if the trail is winding a lot?
Somebody above asked if smart phones use the cell towers for location services and the answer is yes. But it's not that simple… they also can use wifi to speed up your fix (nail down your location quickly). That's why you can often find your location when inside a building… think about it, one day all your favorite stores will be Geo-referenced "inside" the mall! My Motion X GPS app allows me to select Wifi/Triangulation Mode which finds my location while the built in GPS is turned off.
My son and I have tested this on his iPod GPS app, which is amazing when you consider an iPod doesn't have a GPS receiver built into it and can't use cell towers. We can walk around our block and the GPS marker puts us in the middle of the road by pinging the neighbors wireless routers. You don't have to be logged on to search for them, you just need to be able to pick up their signal and the software can triangulate your position.Jan 14, 2013 at 11:20 pm #1943937
"My son and I have tested this on his iPod GPS app, which is amazing when you consider an iPod doesn't have a GPS receiver built into it and can't use cell towers. We can walk around our block and the GPS marker puts us in the middle of the road by pinging the neighbors wireless routers. You don't have to be logged on to search for them, you just need to be able to pick up their signal and the software can triangulate your position."
iPod uses WiFi triangulation to determine its location.
However, "pinging the neighbors wireless routers" doesn't seem like it is the entire solution. The wireless routers do not know their own location much more accurately than maybe the nearest Zip code.
–B.G.–Jan 15, 2013 at 5:30 am #1943955
Ken T.BPL Member
You can always PM Amy L or Andrew Johnson. Both BPLrs. Amy does update that article and has done other posts on the subject here.Jan 15, 2013 at 10:01 am #1944036
Andrew JohnsonBPL Member
@trailbehindLocale: San Pablo Park
Garmins and other hand-held GPS do have better GPS accuracy than iPhones in my experience.
The first iPhone with a GPS (the 3G), which I tested against a Garmin, had very noticeably different track lines, and discrepancies in distance recorded. Over time though, the GPS chips in iPhones and iPads have gotten better – they still aren't the same grade as Garmin units in my experience, but there is also no practical implications for my purposes.
If you are just hiking around, then I doubt you'll notice any meaningful difference. If you need to do things like surveying, avalanche spotting, and other high-precision activities, you might want a handheld GPS. Even for geocaching though, where you need to be pretty accurate, the iPhone works very well.Jan 15, 2013 at 10:34 am #1944050
Buck NelsonBPL Member
What Andrew said: If you are just hiking around, then I doubt you'll notice any meaningful difference. If you need to do things like surveying, avalanche spotting, and other high-precision activities, you might want a handheld GPS. Even for geocaching though, where you need to be pretty accurate, the iPhone works very well.
That was my experience with the GAIA GPS on my iPhone 4s on my Desert Trail hike where I was using it to mark, and sometimes relocate, buried caches. I had a Garmin Etrex Legend HCx for a backup, and I was able to rely on both of them.
The iPhone 4s worked well for me, I'd expect it would work well for you.Jan 15, 2013 at 10:51 am #1944058
Robert KellyBPL Member
@qiwizLocale: UL gear @ QiWiz.net
with a v4 and now a v5 iPhone, running Gaia GPS for topo map and track downloads and to see my position; running CoPilot Live for road turn by turn navigation. Neither needs a cellular signal to work. Both use maps that are downloaded to the phone.Jan 15, 2013 at 11:38 am #1944074
I have been using an app called "Topo Maps" with my iPhone for a few years and really like it. I think it was around $5 for the app and then all map downloads are free. The maps are USGS 1:24,000 topographical maps. I don't use any of the advanced functionality, basically I just use it to see where I am on the topo map (since it uses the phone's GPS). Most of my hiking is in the Grand Canyon and it's been great to keep me on track when on less-traveled trails and also to see the remaining distance before I reach my daily destination. Here's a screenshot:Jan 15, 2013 at 12:23 pm #1944092
Thanks for the great info folks. Seems like the consensus is that the Garmin receiver is technically better, but not enough to matter to most people for "hiking around" purposes. Great info and discussion!
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