RFI: GPS Signal Reception With New Tablets

[Dog Guy]

My 5 year old android tablet went to tablet heaven last week, so I'm looking to replace it. I'm tempted to go with a 2019 Ipad Air. Primary usage is with mapping apps such as Gaia, in areas with no connectivity: no WiFi, no cell, no nothing but what's on board and usable offline.
When we bought tablets years ago (when Ipad Air was the newest thing), you could not receive GPS signal on the tablet unless you got a cell-capable model. The tab used the cell antenna to receive GPS signal. A WiFi only model had no cell antenna so it couldn't receive the GPS signals. You didn't need a data plan or any connectivity: just the cell antenna had to be in the device. This was true for both Ipad and Android.
For 2019: is this still the case? Sales Guy at Best Buy is certain that you can't get GPS signal without a data plan and connection and that Garmin GPS units get signal from Garmin satellites. Seriously. Other BB Sales Guy is certain that the current WiFi models have a GPS antenna built in and you don't need the cell model or a data plan. Lord Googlemort provides both answers in roughly equal measure. Apple Tech Support is certain that you need a data plan and connection to receive GPS signal on a new Ipad Air, can't grasp the idea that "GPS signal" and "data" are two different concepts, and seemed rather stumped that there are places where you don't get network access.
So: does anybody have a 2019 Ipad Air that they have used with WiFi off and no network connection to verify ability to receive GPS signal for use in nav apps such as Gaia? Any idea on the current state of Android tablets?
I know I could by an external GPS antenna but I'd prefer the simplicity and durability of built-in reception.
Thanks.

[Dan_S]

I bought an iPad last year for use in a similar application.

Get the cell capable model, and you’re able to get GPS signals, without a data plan.


It’s simple. It’s easy. I’m amazed that these guys that are supposed to know more about tech stuff than me don’t know this stuff...

[RJ]

AFAIK no iPad without a cell plan has a built-in GPS. Here's an option if you buy an iPad without built in GPS, perhaps:

https://gps.dualav.com/explore-by-product/xgps150a/

My WiFi only iPad however seems to be able to work out where it's at fairly well, using WiFi alone. I'm consistently surprised how accurate it is.

[Dan_S]

AFAIK no iPad without a cell plan has a built-in GPS. Here's an option if you buy an iPad without built in GPS, perhaps:

https://gps.dualav.com/explore-by-product/xgps150a/

My WiFi only iPad however seems to be able to work out where it's at fairly well, using WiFi alone. I'm consistently surprised how accurate it is.

You buy a cell-capable model directly from Apple, and you’re in business. I didn’t get a data plan through my carrier, as I didn’t need to for use with the specific app I needed to use the device with, just GPS connectivity.

[RJ]

You buy a cell-capable model directly from Apple, and you’re in business. I didn’t get a data plan through my carrier, as I didn’t need to for use with the specific app I needed to use the device with, just GPS connectivity.

Cool, good to know.

[Dog Guy]

Thank you both. I asked the same question via email to a lot of smart SAR folks. It surprises me how few know the details of their device (wifi only, cell capable, logged in to wifi or network, etc.) The best answer I got was from a very bright guy on our local team. He said:

"I can say with confidence the following:

0) Garmin does not own a multi-billion-dollar satellite constellation. I think we’re all on board with this one.

1) Only iPad models with cellular have assisted GNSS/“satnav" (not only GPS, but also BeiDou, Galileo, GLONASS, etc). This is because the satnav modem is actually built into the cellular modem chip, which is an FCC requirement. Most Apple devices (including iPad Air) also have a barometric altimeter built-in.

2) You do not need to purchase an active data plan to use the GNSS receiver. The GPS on my iPad Pro works perfectly fine without a data plan or SIM card, and I use it with Gaia and Waze with satellite ±3m precision.

For interest:

3) Most devices now (iPad included) have “assisted GNSS” which does not mean what people usually think. The chip and software are fully capable of tracking satellites without any internet or cellular connection, just like a Garmin handheld. Satellite navigation relies on two main things: knowing the exact orbit of each satellite (“ephemeris” data), and knowing how far away the satellite is, by seeing how long it takes their timecode signal to reach you. The “assisted” portion refers to the fact that, with an internet or cell connection, the ephemeris data for the satellite’s orbits is downloaded from a server, rather than from the satellites themselves. GPS satellites constantly transmit ephemeris data interspersed between sending their atomic clock’s timecode. The user’s device uses this ephemeris data, alongside the clock signal, to do the location maths. The problem is each satellite sends the orbit calculations for the entire constellation of satellites, and with such low data rates it takes about 15 minutes to transmit all that information. That is why it can sometimes take that long to get a “cold fix” if you haven’t used a Garmin for a long time. If used recently, the unit caches the data and only needs to hear “updates” (which are shorter and come more frequently) until the ephemeris data expires. With assisted GPS, this ephemeris data comes directly from the US Air Force eliminating the need for a 15 minute warmup. The other benefit is that with cellular connection or WiFi, the devices gets (is always tracking in the background; low energy) an instantaneous “rough fix” which makes the mathematical triliteration of GPS satellite fix much quicker, for reasons that I’m happy to explain in more depth, but generally involves atomic clock error correction that would typically require a fourth satellite’s signal to attain. Also you need internet to load maps, and use CalTopo, of course.

4) Because devices have the capability to see multiple constellations (GPS, GLONASS, BeiDou, Galileo) they routinely achieve much higher location accuracy and stability than handheld GPS units like an old Garmin 64 or Garmin Oregon. Newer Garmins, like the watches and the 66/64x support multi-GNSS but still typically not BeiDou.

Hope that helps!"

[Cookie Monster]

Like a previous post, buy an iPad direct from Apple with it being cell capable.

I have a crew that collects data directly on an iPad way out in the woods, I think our iPad Pro’s are two years old and work great.

There is no reason to buy another stand alone GPS unit. iPads are cheaper and have way more function then the higher end Garmins.

I would roll with an Air since LifeProof is making a case for it, that is the only waterproof case I know of. I like the size of the Mini better but no one is making a decent case for it. I’ve tried the SealLine bags but it is hard to use the screen through them. OtterBox cases are good with the closed up screen protector and space for the Pencil but not waterproof.

Also my crew finds the Apple Pencil useful because you can run the device while still wearing gloves and it’s a pain to collect data in the pouring rain as the water dropping makes things hard to run. I’ve run them by pointing the back to the sky to keep the touchscreen free from pounding rain.

[Dog Guy]

Thanks for the tip on the waterproof case. That's always a challenge with Android tabs. Too many players, not enough market dominance for the case makers to produce for all the options.