IPad for Navigation FAQ 2018

[Ferrari]

Originally Posted by Juho

> 1. Is the internal GPS of some of the cellular chip iPads suffcient or adequate for offshore use and coastal use without having a cell phone contract? I am aware that not all iPads have the internal GPS (only those with a cellular chip do, according to Apple). I would not register the cellular SIM card (I don't want to use the iPad with a cellular data plan) so does that make a difference? My understanding is that all that matters is that the iPad have the cellular GPS chip, and that one does not need to be on a cellular system (or contract) to use the GPS functions in apps while offshore. Is that correct?

I didn't bother to find out the technical details but made a practical test . I used two iPads in parallel in a car. One had a valid SIM and the other had an inactive SIM. I did not notice any meaningful differences in performance. Both drew an accurate enough track of the car.

A contract is not required for the cellular iPad to utilize the GPS.
The non cellular iPad will not have GPS offshore
The Cellular iPads have a different internal chip to the Non Cellular. IE real GPS Chip
Non cellular utilize clever triangulation from cell towers to calculate position
Make sense? No Towers No Position.

[a64pilot]

Actually the Cell equipped IPads will use triangulation to buffer or augment the GPS chip, just as a Cell phone does. A cell equipped IPad is essentially an IPhone as far as Nav goes.
Lose a Cell signal and Nav is degraded somewhat.
The internal GPS chip is not as good as determining position and course and speed as a stand alone Bluetooth GPS, however I’m sure 99% of the time it’s fine for a 6 Kt Sailboat.
It’s similar to your plotter, it works fine, but works better with an external antenna.

[Juho]

Originally Posted by Ferrari

A contract is not required for the cellular iPad to utilize the GPS.
The non cellular iPad will not have GPS offshore
The Cellular iPads have a different internal chip to the Non Cellular. IE real GPS Chip
Non cellular utilize clever triangulation from cell towers to calculate position
Make sense? No Towers No Position.

I was hoping to see some minor differences between GPS and assisted GPS, but I didn't observe any significant differences. I could have tested the startup performance (delay to get the system running) more. Maybe I'll make another try tomorrow and see if I can find something that could influence navigation (even a bit).

[2big2small]

Originally Posted by Ferrari

A contract is not required for the cellular iPad to utilize the GPS.
The non cellular iPad will not have GPS offshore
The Cellular iPads have a different internal chip to the Non Cellular. IE real GPS Chip
Non cellular utilize clever triangulation from cell towers to calculate position
Make sense? No Towers No Position.

You are confusing matters slightly. To the best of my knowledge, non-cellular iPads do not have any cellular ability whatsoever and therefore can’t triangulate their position from cell towers. Instead, they triangulate based on the signal strengths of wifi networks, which works reasonably well enough in dense cities where you’re continuously surrounded by dozens of wifi networks. But as soon as you hit the highway for example, you loose your position.

Cellular iPads have their true gps chip, plus triangulation from cell towers, plus triangulation from wifi networks. My experience too confirms that just the gps chip works well enough when sailing on the open ocean.

[gjorgensen]

Originally Posted by 2big2small

To the best of my knowledge, non-cellular iPads do not have any cellular ability whatsoever and therefore can’t triangulate their position from cell towers. Instead, they triangulate based on the signal strengths of wifi networks, which works reasonably well enough in dense cities where you’re continuously surrounded by dozens of wifi networks. But as soon as you hit the highway for example, you loose your position.

Not quite. The GPS receiver is built into the cellular chipset in the iPad, so WiFi-only models have no location ability at all. There is no such thing as WiFi triangulation by the device unless someone writes a custom app to do it in a given area. The iPad has no idea where the APs are located in the real world or maps of any sort so it has no way to determine location. The lack of location ability in WiFi-only iPads comes from Apple not including a regular GPS receiver on those models as many Android vendors so.

WiFi triangulation exists but in the opposite direction - in a location-enabled WiFi system, access points report signal strength upstream to a box with maps which triangulates a position. It could potentially feed that back to a device that is actively connected to such a WiFi network. But this is usually only done for indoor navigation, and only works with devices that do location blinks to drive it (which most devices do not do). That is actually what I do for a living so I know the space pretty well.

Also, to be clear A-GPS (cellular assisted GPS) is not doing any sort of terrestrial triangulation either. It uses the cellular network for any of several things: Local position and time data to shorten startup time for the onboard GPS receiver, better GPS calculation from raw GPS receive data sent from the phone to a network server, or a roughly calculated position from a network server fed back to the phone to augment what GPS data it does have (very helpful in poor reception areas).

[a64pilot]

Originally Posted by Juho

I was hoping to see some minor differences between GPS and assisted GPS, but I didn't observe any significant differences. I could have tested the startup performance (delay to get the system running) more. Maybe I'll make another try tomorrow and see if I can find something that could influence navigation (even a bit).

It’s likely to be more of an issue with an airplane at > 100 kts, and likely also an issue of the Bluetooth GPS receiver being on the glare shield and having a much better view of the sky as opposed to the IPad being inside of the cockpit, which is of course usually aluminum and will attenuate GPS signal strength somewhat.
Plus one has to think that a purpose built device for receiving a GPS signal may be better at tracking GPS signals than an add on chip within a device.

The difference in number of satellites tracked and signal strength, DOP / EPE between my B&G Zeus and my Vesper 8000 is incredible, the Vesper has the external antenna is I’m sure why. A Bluetooth GPS is analogous to an external antenna.

[2big2small]

I can assure you Apple uses wifi networks for its location services. Years ago I was already navigating cities on an iPod Touch, no cellular whatsoever there. And there’s also their system message asking you to switch on wifi to improve location services.

Apple uses crowd sourcing to determine the locations of wifi networks and cell towers and in turn, by walking amongst those beacons, you get to know your approximate position even if your ios device can’t get a gps fix (or doesn’t have a gps).

Originally Posted by gjorgensen

Not quite. The GPS receiver is built into the cellular chipset in the iPad, so WiFi-only models have no location ability at all. There is no such thing as WiFi triangulation by the device unless someone writes a custom app to do it in a given area. The iPad has no idea where the APs are located in the real world or maps of any sort so it has no way to determine location. The lack of location ability in WiFi-only iPads comes from Apple not including a regular GPS receiver on those models as many Android vendors so.

WiFi triangulation exists but in the opposite direction - in a location-enabled WiFi system, access points report signal strength upstream to a box with maps which triangulates a position. It could potentially feed that back to a device that is actively connected to such a WiFi network. But this is usually only done for indoor navigation, and only works with devices that do location blinks to drive it (which most devices do not do). That is actually what I do for a living so I know the space pretty well.

Also, to be clear A-GPS (cellular assisted GPS) is not doing any sort of terrestrial triangulation either. It uses the cellular network for any of several things: Local position and time data to shorten startup time for the onboard GPS receiver, better GPS calculation from raw GPS receive data sent from the phone to a network server, or a roughly calculated position from a network server fed back to the phone to augment what GPS data it does have (very helpful in poor reception areas).

[gjorgensen]

Originally Posted by 2big2small

I can assure you Apple uses wifi networks for its location services. Years ago I was already navigating cities on an iPod Touch, no cellular whatsoever there. And there’s also their system message asking you to switch on wifi to improve location services.

Which is not done by triangulation, which is what I was pointing out. The iPad has to be connected to WiFi, and reports the MAC of the serving AP and the RSSI of the AP as seen by the device (actually reported TX power by the AP + RSSI) to an Apple server. If Apple has that AP in its database along with the location of the AP, it will then calculate a proximity to it and report those coordinates back to the iPad. As you move around APs it can eventually determine where on the circle your are and get a rough location. This same technique can be used on the iPad itself if someone can download the database and maps of the known APs. TechCrunch and others have more details on how this works.

[StuartSailor]

Good Evening All,

I’m very happy to have found this thread as I am heading to the boat show">Miami Boat Show this weekend and I’m looking to upgrade some of my electronics. While I have found much of this information extremely helpful, I am still a bit confused as to how best to set up what I think I need/want. Under the premise of asking 10 boaters 1 question and getting 12 different answers and all of them being correct, let me pose this. Your feedback is greatly appreciated.

Quick background. I’m mainly a coastal cruiser out of Stuart, Florida heading to the Abacos for the first time this summer. I also plan on cruising the Keys occasionally and hope to go to NY in the summer of 2019 and do an ICW rally on the way back. I’m sailing a Tartan 37.

I have a basic SH VHF, not connected to my GPS, so non-functional DSC (I believe). I would like to replace it with the new SH GX6500 for the GPS and the AIS send/receive. I realize that this unit is not yet available but I’m hoping it will be available by June. I was planning on using a splitter to use my VHF antenna.

I have an iPad Pro without cellular and based on this thread, w/o GPS. I have the iNavionics app downloaded and was happy to see there are a lot of iNavioncs supporters out there so perhaps I’ll keep that instead of evaluating Garmin Bluecharts and Open CPN and just heard about iSailor. I was considering a wif fi booster (wifi ranger, wave, or Shakespeare) but don’t feel I need a cell phone booster since phone calls are less important to me than internet access. However, now I’m seeing the Wirie Pro which I’d never heard of and is supposed to be both a wifi and cell booster so that’s something I didn’t see coming. I have a Garmin 541S at the helm which is 6 years old with a small screen. I was hoping to keep it despite it’s small space (I’m concerned it will be too crowded with AIS vessels) but depending on the spend for the other equipment I could consider upgrading to a 7” or 9” model.

So trying to put this all together. Do I still need a Vesper device so everything talks to one another? I want to be able to use my ipad crossing the Gulf Stream as many have mentioned. Can I connect my iPad Pro (smaller screen model, 9” I think) to my VHF to access the GPS there? If so, I am assuming I can see the AIS vessels on my ipad as well. Is the wirie pro a no brainer or should I stick with a wifi booster only?

Sorry if I’ve taken this thread slightly askew but man, I can use some guidance. If I’ve forgotten something that will help you help me, please let me know. Thank you all in advance. I’m hoping to spend some money at Miami Boat Show!

Jesse
S/V Sailsman

[StuartSailor]

Wow! Sorry, I didn’t realize I posted so much information. Sometimes I don’t read the REALLY long ones either.

Jesse

[2big2small]

Originally Posted by gjorgensen

This same technique can be used on the iPad itself if someone can download the database and maps of the known APs.

Which is precisely what it does.

[LeeV]

Originally Posted by sailm8

This is the mount I used. https://www.amazon.com/iPADKET-DURAB...+iPad4+1+2+3+4

It has screw holes that I used to mount it where my deceased GPS lived. I used Navionics and if it rains, a gallon ziplock bag works fine.

Can you describe where/how far apart the holes are in the case? I don’t have tons of bulkhead space available.

Thanks!

[Juho]

Originally Posted by a64pilot

It’s likely to be more of an issue with an airplane at > 100 kts, and likely also an issue of the Bluetooth GPS receiver being on the glare shield and having a much better view of the sky as opposed to the IPad being inside of the cockpit, which is of course usually aluminum and will attenuate GPS signal strength somewhat.
Plus one has to think that a purpose built device for receiving a GPS signal may be better at tracking GPS signals than an add on chip within a device.

The difference in number of satellites tracked and signal strength, DOP / EPE between my B&G Zeus and my Vesper 8000 is incredible, the Vesper has the external antenna is I’m sure why. A Bluetooth GPS is analogous to an external antenna.

Our old, now obsolete plotter used an external GPS antenna. We have however had no complaints about the performance of the iPads inside the pilothouse. They draw a quite accurate and detailed line when we sail, and also location on the map seems to be quite accurate.

I have used also a better GPS antenna in a tractor. It makes it possible to steer the tractor in 50 cm accuracy or better. But at sea similar accuracy is usually not needed. Normal iPads seem to do fine.

P.S. I compared the performance of GPS and assisted GPS again. No other observations except that as expected, when cold starting the iPad with non assisted GP, finding the location may take quite some time, but less than a minute. In navigation that is normally not a problem, but maybe in some special circumstances.

[OrinocoFlo]

My iPads work great!

Flo

https://www.youtube.com/watch?v=roLIEIjsd18

[dukey]

Hi
I am in Europe and travel up and down the West coast of Europe using my iPad Air 2 with Navionics charts on it. I also have a Raymarine E120 and a Magellan and an iPhone. The Raymarine is binnacle mounted but not in use at the moment due to an alteration around the supports etc. the iPad is wired to a usb with a 10’ long wire (Amazon) and is mounted under the cabin roof facing out the companionway.
Pros. Good charts
Easy to see when using
Being Navionics no obvious glitch’s

Cons. €115 per year for northern Scotland to the canaries with the Med included
Have to buy twice again for my iPhone and my Raymarine.
When charging which has to stay on all the time ( or the time you need it it will be dead ) the charger goes slow
sometimes
People wanting to use it and removing it from the mount and unplugging it. 🤬 Short rations for a week