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I've been reading a lot today about android and iphone devices being used for spatial data collection in the field and it sure seems to be that single purpose devices such as the extremely popular Garmin eTrex are a dead end. Why buy something with a tiny screen, no ability to add custom data collection interfaces, cost-plus base maps, and no picture taking when you can get all that and more for free or very cheap with a tablet/phone?

As near as I can tell so far the only real advantages a real GPS has over these other devices are ruggedness and extended battery life. Unless maybe accuracy? How does the accuracy of a GPS-enabled smart phone or tablet compare with a consumer grade "real" GPS? What about when off-grid? What about cold-start time-to-lock?

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Are these options mutually exclusive? I'd like to find a way to use a real GPS receiver (with no UI) connected to an iPad (via BlueTooth) to collect RINEX files. Would like the option to do either RTK or post processing. –  Kirk Kuykendall Mar 29 '12 at 17:02
    
Not necessarily exclusive @Kirk. I was thinking about "the thing you stuff in your pocket". Years ago we tried ipaq handhelds with external gsp receivers. It was a real headache managing the cable and connections. It got lost, twisted, damaged, and allowed dust and water in too easily. A bluetooth connection would ameliorate that. –  matt wilkie Mar 29 '12 at 19:25
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The above mentioned paper by Paul Zandbergen (Accuracy of iPhone Locations: a Comparison of Assisted GPS, WiFi, and Cellular Positioning) can be downloaded from here: paulzandbergen.com/PUBLICATIONS_files/Zandbergen_TGIS_2009.pdf –  user6071 Apr 10 '12 at 20:07
    
The Garmin Glo is a great improvement. –  Willy Mar 27 '13 at 10:04
    
Im running a BT-339 with Android Blue tooth GPS provider and it gets me sub 1 meter accuracy picking up svn 37 41 and 46 on other phone –  user21613 Sep 1 '13 at 16:33

12 Answers 12

up vote 14 down vote accepted

I saw a study at New Mexico State comparing an HTC G1 and a Trimble Juno. You might want to check it out. Here are the study's accuracy test results:

enter image description here

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Interesting that, in this test, the android device was more accurate than the commercial grade gps. Contrast that with the report from Australia ( below ) and it's clear one needs to test for what's relevant in one's own region. Thanks for the link. –  matt wilkie Mar 29 '12 at 15:56
    
De nada. Do note that the the G1 is a first generation Android device so things might have actually gotten better since then. Searching for more comparisons :) –  R.K. Mar 30 '12 at 3:49
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I've accepted this as the right answer since it references a real study and not just anecdotal info. It really can't be be considered "the" right answer though without combining important points from the others (like sometimes android locations are cell network assisted, the importance of knowing the chipset, and local geography can make a big difference). –  matt wilkie Apr 3 '12 at 18:52
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The interesting thing here is that the test was in an urban environment, in which cell phones/tablets can benefit from Assisted GPS (assisted by WiFi hotspots and cell towers). Go outside their coverage area though and I am willing to bet Differential GPS (assisted by ground stations meant to calculate corrections) will outperform any time. The question is what is your application. In a city, a handheld GPS will get more errors by the bouncing of signals (multi-path interference), while a surveying GPS will not even blink at that (see Trimble R10 for example) –  Michalis Avraam Oct 9 '12 at 23:11
    
Note that you really want have PDOP and HDOP values to make some kind assumption about accuracy –  simplexio Sep 1 '13 at 19:21

As near as I can tell so far the only real advantages a real GPS has over these other devices are ruggedness and extended battery life. Unless maybe accuracy?

Pretty much, and that's easily enough for me. I've recently bought another Garmin Oregon, which I use for hiking and cycling. For these use cases, a smartphone will never really cut it:

  • All day track recording (eg, 8-12 hours per day)
  • Mountain biking/off road riding
  • Use in the rain
  • Quickly consulting while hiking - means it needs to be accessible and will be bash into things

A dedicated GPS is also much easier to hold comfortably, starts up quickly, and locks solidly onto the GPS signal especially in difficult terrain.

Garmin last year introduced the Monterra, which is a kind of hybrid device: an Android-based GPS which lets you run internet-based apps. My perspective was a bit the opposite of yours: I couldn't see much point in fancy apps on the GPS. I'll probably have my smartphone with me if I need to do anything like that, whereas while I'm on the bike, I just want the GPS to perform very well as a GPS.

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There are a huge number of devices to choose from, and it is difficult to broadly say that one family of device are more precise than others. It is better to compare accuracy based on real life tests. However, there are a few things to consider:

  • Chipsets. Dedicated GPS, and Smart Phones use a chipset to actually perform the GPS calculation. The accuracy and capabilities vary. Some chipset's are optimized for urban canyons and are particularly suitable for smart phones (SIRFstar III). Others can track a greater number of satellites concurrently and feature SBAS augmentation. Some cell phone chipsets may outperform those used in dedicated devices. Even some professional grade GPS (Nomad 900G) units ship with less accurate consumer grade chipsets.
  • Antenna. The placement and quality of the antenna effects GPS accuracy. Some dedicated GPS units have external antenna's instead of the internal antenna typical in smartphones. They may also feature an antenna socket to allow an aftermarket antenna to be added.
  • Assisted GPS. It is possible to improve accuracy using data from non-satellite sources. GPS almanac and ephemeris information can be downloaded using a smartphone radio, or uploaded using dedicated GPS software. Smartphone's can also use cellphone towers to aid in positioning. This can improve accuracy and reduce time until first fix.

In summary, it is worth looking at the chipset, antenna specification, and Assisted GPS capabilities to determine the likely performance of the device.

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Another interesting question would be: At what point does a "real GPS" become a tablet, and vise versa? We have dedicated Android based e-readers; it's not hard to imagine dedicated Android based survey quality GPS units. –  cwa Jun 10 '13 at 17:43

This article on high accuracy GPS capture with an andriod platform is very encouraging - http://www.3-gis.com/news/pr6-20-2012 . Hopefully in a year or so one could buy an andriod device, a rugged case for it and an external GPS as an alternative to a Trimble with Terrasync (which in my opinion is incredibly overpriced). That would be the day...

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sounds encouraging. It'd be nice to have some articles about it which aren't a press releases from the company(ies) involved; perhaps in the fullness of time that will come. :) –  matt wilkie Feb 1 '13 at 17:21

I've had the chance to do some comparisons between iPhone data collected from a mountain bike with the data collection from a Garmin GPSMAP62sc. They were fairly close for much of the ~30km route. However, at one point they were 100m+ out. This was on a service road (so no tree cover overhead but trees to the side) and close to a river canyon and on the side of a mountain.

The Garmin data lined up with other sources of data. The iPhone appeared to be the one at fault.

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I just happened across another published study on this. Paul Zandbergen, 2009, Accuracy of iPhone Locations: a Comparison of Assisted GPS, WiFi, and Cellular Positioning. Transactions in GIS, 13(s1): 5-26. (PDF, 1mb)

They found median errors of 8 m with GPS-assisted 3G iPhones, down to median 47 m errors for WiFi, and median errors of 600 m (!) for cellular positioning, all compared to GPS alone.

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The best accuracy you are going to get with a phone or tablet device is 20-30 meters. So you have to ask yourself what is the purpose of your GPS? If you intend on navigating back to the asset in question, do you really want your users within 20-30 meters, is that accurate enough for what you are attempting to capture.

What the higher end GPS receivers give you like the Trimble GeoXH 6000 series, is 4 inch accuracy or better as they just released an add on for decimeter accuracy. In my case we are in the utility industry and we use a VRS(Virtual Referencing System) in Ohio which allows us to achieve 4 inch accuracy without any post-processing, it is real time in the field.

This means less overhead back in the office and we can store all GPS information in the attribute tables as data is being captured using the AddXYZ applet for ArcPad. Using the higher end equipment coupled with higher end software like ArcPad or TerraSync allows you to make checking data in and out and edit operations seamless.

So again, what is the end goal and does the money you spend up front give you a ROI in the long run. If automation, easy of use, and integration mean a lot to your company then I would suggest using Esri(ArcMap coupled with ArcPad), Trimble(GPS Correct, possibly GPS Analyst if you are going to post process), from here use a geodatabase(file or SDE). Now you can automate getting data in and out seamlessly using python or model builder. Then getting the data back in can be done using the same scripting methods as well.

Think of GPS units like cars

Phone/Tablets - Like a pinto Trimble GPS units - The cadillac

If you are just going to use the phone/tablet setup for attribute collection you should be fine, they are perfect for that. But if you expect to navigate back to the asset good luck.

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+1 The points re: thinking about the end goal and workflow are good. -1 for the first sentence, which is a claim without backup. e.g. where's the data man? ;-), and kind of the point of the question. I've often seen ~30m errors with a dedicated gps unit like Garmin eTrex or GPSMap (and the Q is focussed on comparing consumer GPS units to smart phones). –  matt wilkie Apr 10 '12 at 21:03
    
It is true that in general you get what you pay for, on an exponential scale (i.e., the difference in cost between "good" and "best" will be huge, even if the difference in performance isn't). As GPS becomes more and more commoditized, the difference between "real GPS" and standard, consumer-grade GPS will get smaller and smaller, and the cost will get further and further apart. "Pinto" vs "Cadillac" may be true today, but tomorrow it will be more like "Limo" vs "The Beast" –  cwa Jun 10 '13 at 17:48

As shown by the comparisons mentioned above, the accuracy of GPS units in phones is pretty much on par with dedicated data collection units - while stationery. I have been working on developing a vehicle tracking application and have noticed that the update frequency between android devices can vary, which affects the accuracy of tracking a vehicles route at higher speed and when it turns corners a lot, versus along a straight road. e.g. My phone updates GPS location at 0.5Hz, yet my tablet updates at 1 Hz. Even at just 60km/h, the vehicle could have moved about 17m, obviously this makes a big difference in plotting a path around a corner, or determining speed between 2 GPS location readings.

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Very interesting, thanks for the numbers. I encourage you to publish your results at some point, when that makes sense for the project. –  matt wilkie Apr 5 '12 at 19:33

Some students at Skidmore College recently did a simple experiment and found the differences were several meters apart from one another, but that's all.

http://academics.skidmore.edu/blogs/onlocation/2012/03/30/smartphone_accuracy/

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Many cell phones and tablets will also use Wi-Fi data to assist their location fix. Google has a huge database of wireless access points and their locations, when the phone's Wifi is turned on it will check nearby wireless APs and use that to narrow down your location quickly. It's the same idea as using a cell tower to locate you, but a Wifi network's range is much smaller so the location is more accurate.

Of course, if you're in the middle of nowhere, this ability is worthless. So if you have a phone or tablet with GPS built in and you want to test its time to first fix and accuracy, turn off Wifi first to get a more accurate idea of how it will perform when you're out in the field with no Wifi networks nearby.

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We have noted that with even some of the more noteworthy (commercial quality not retail) tablet makers, the GPS is not strong enough for central regions of Australia or when there is any kind of interference. Whereas say GETACS maintain a connection even when indoors. Cold boot times can also be in the double digit minutes for the tablets too.

This may be in part as the tablets and some phone receive a small file via the telco towers to coarse locate that isn't avialable in regional areas.

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I am getting going with doForms which is built on the ODK system for android. For Natural Resource Applications there is just the ticket. Previously I have run QGIS on the a 13" laptop with a gps plugged in, but doForms is miles ahead of this, because you are trying to catpure data - not make maps. So my suggesting is the hardware is more than appropriate, Android and iPhones, it is just a matter of the software maturing a little. doForms will give you a free go, and the paid account is relatively trivial for professional data capture.

doForms does take 10s of seconds to get a location, but it gives you count down of this accuracy so you can curtail the final processing if desired.

I also use a sony gps enabled camera, it's gps is a lot faster but that is because it is always on and sips away at the battery all the time.

ciao

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