The Galaxy S4 has a Barometer | Hacker News Reader

The Galaxy S4 has a Barometer

cumulonimbus.ca

42 pointscryptoz45 comments

I'm interested in what the accuracy, stability and precision of this barometer are. For the use case that they were put into that phone (and the price point it implies), I am unsure whether data reported from these phones will be useful for PressureNet.

Longer explanation: in the parlance used for pressure measurement, a barometer is a low-pressure absolute gauge (although what they pack in the phone is a sensor or transducer rather than a full gauge for obvious reasons). In order to measure absolute pressure, it needs to pack a good source of vacuum to be used as one of the differential inputs. And it needs to do it real small and real cheap. I suspect they're using a piezoresistive or capacitative sensor for this pressure range, which both have a significant tempco, and they almost certainly can't do a valid temp-comp on the part for cost reasons (you can sort of bullshit it by characterizing the lead unit and applying that to everything based on a curve fit, but the results are not great).

Sensors in this form factor and for this price point might be accurate to within +- 2.5%, which is not terribly useful for a barometer for weather purposes.

Somebody posted a link to pressureNETs data:

https://news.ycombinator.com/item?id=5380672 http://pndv.cumulonimbus.ca/

If you zoom in on a location that has lots of people (say, New York City), you can see the readings moving together. That suggests some utility.

More interesting than the barometer is the thermometer in the S4. Has any other phone included one yet? Crowd-sourcing of weather data is an interesting concept, but I wonder how useful a thermometer will be when phones will most often be in pockets, indoors, in a car, etc.

Many android phones have a thermometer. It precisely measures the weighted average of the ambient temperature and the waste heat from the processor. In other words, just this side of useless, because the thermometer is next to a heater.

Not very useful at all. To accurately measure temperature you really need a Stevenson screen (http://en.wikipedia.org/wiki/Stevenson_screen). But furthermore, this needs to be located in a good location with attributes such as good air circulation, lack of buildings, concrete, trees, etc. It's often impossible to meet all these conditions in an urban area, which means you're really measuring a micro climate. While there are some sites that crowd-source data from personal weather stations, there's really no guarantee that people have followed good guide lines with the placement and installation of their weather station. It's sometimes obvious when this is occurring because you see some pretty large variations in temperature in more or less the same neighbourhood.

But what if many people measure their local microclimates? Couldn't one 'add up' all those measurements to get the 'real' temperature out of it?

Would be like a high resolution heat map.

Didn't the S3 already have this, or does only my Note II? I've always wondered what it was for (GPS apparently, says another comment here).

Yes, the S3 has one too.

Most new-ish Android phones have a barometer. It assists in determining a rough altitude to make GPS lock faster.

Hence the ability to use apps like this to track barometric pressure across smartphones and track trends: https://play.google.com/store/apps/details?id=ca.cumulonimbu...

While direct, immediate benefit to the user seems limited, there are some interesting possibilities with this.

Weather forecasts made up from thousands of highly localised data points? That feels like something Google would want to be involved in - a highly data centric way of improving something we already do which is of interest to many people.

Depends on accuracy obviously but maybe in the future.

Sorry, this is nothing new at all. Here is a list of smartphones which have a build-in barometer sensor to measure atmospheric pressure to improve the location services: Google Nexus 4, Samsung Ativ S i8750, Samsung Galaxy Nexus i9250, Samsung Galaxy S3 i9300, Samsung Galaxy S3 LTE i9305, Samsung Galaxy Note (N7000), Samsung Galaxy Note 2 (N7100), Simvalley Mobile XT-710 Apogee, Takwak tw700.

Did you read the article? It says so too. You are sorry that you just read the title?

A Barometer is present on a few other Androids, so I assume it comes free as part of another chip. It's rarely listed as a feature though, which makes me think it's only enabled because it's there.

Has anyone checked the calibration/reliability to see if it's actually worth using?

Quite a while ago, I remember seeing an article on HN about Google encouraging new Android phones to have barometers, and some reasons for it (possibly something to do with faster/more accurate GPS fixes).

That's correct. As I understand it, you can get a reasonable altitude estimation from the barometer.

I'm pretty sure it was in the S3 as well.

Yep, and the Nexus 4 has it too.

I suppose now there is going to be an app to measure the height of a building.

http://www.snopes.com/college/exam/barometer.asp

Does this help running/cycling apps where folks want to measure altitude gains more efficiently?

The coolest thing about the barometer foe me, is that you can do interesting pedometer + altitude change sorts of apps. Walking 10,000 steps with 2,000' change in elevation is a lot more calories than 10,000 steps with 0 change in elevation :-)

Had no idea my Note II had a barometer. Just got pressureNET.

I knew; I just didn't know what to do with it.

I've had fun with the barometer in my Nexus 4 - with the app 'Sensitive Altimeter' ... on flights I can see at what elevation the cabin is pressurized to :).

Does Galaxy S4 have a kitchen sink?

A barometer is present in new smartphones as a part of the GPS because GPS only provides accurate X/Y positioning, and using barometric data (which varies predictably as elevation changes) allows the GPS to have Z data as well, giving it a better representation of your location. (This is the best explanation I've seen, please correct me if I'm wrong).

If you want to donate your barometric data for study, I recommend checking out PressureNet https://play.google.com/store/apps/details?id=ca.cumulonimbu...

The PressureNet dev(s) are active on HackerNews and have made a couple of posts about the app.

For the record, my Galaxy Note II has a barometer as does the Galaxy S3 -- meaning the S4 didn't change anything in this regard!

GPS provides accurate 3D positions. However if you know roughly your position the GPS fix can be acquired more quickly. So the barometer only helps you with an estimate Z pos, which helps you get the GPS fix faster.

If you have line-of-sight to only three GPS satellites then you don't have enough information to compute your altitude [1]. If you can see four satelites, the altitude can be computed.

edit: spelling

[1] http://gis.stackexchange.com/questions/12866/why-does-gps-po...

Just tried it out and my phone doesn't report any position (however inaccurate) if it's only seeing 3 satellites. Also, although it's possible in principle, I doubt the timing information on a consumer phone is accurate enough to get a possible fix from 3 data points.

Ah, yes of course :)

If you have line-of-sight to three GPS satellites, you can compute all three of your coordinates (one will be impossible and can be ruled out), assuming you have an atomic clock locally. If you're like most of us and don't, then you need a fourth (and fifth, and sixth, and seventh) satellite for timing adjustments. Until then, you'll get no fix.

You don't need a local atomic clock for fairly accurate positioning using 3 satellites it just takes longer. Basically, what you need to know is distance from each satellite and an atomic clock let's you find that directly. However, GPS satellites are moving so much faster than you that at over time you narrow down the possible distances involved fairly quickly. Though this does take a lot of processing and is not on any consumer device I know of.

Also of note, phones get a reasonable fix using base towers which can speed up GPS calculations though I don't know of any phone that does this.

Almost all phones do use the base tower to speed up getting a fix with Assisted GPS: http://en.wikipedia.org/wiki/List_of_devices_with_Assisted_G...

The barometer gives you better resolution on the Z pos. So it's useful for measuring changes in altitude and the like, provided the weather conditions don't change (resulting in a change in atmospheric pressure). Though without some kind of calibration, you can't determine your altitude from the barometer alone. It can also be useful to calibrate when enough GPS satellites are visible, then continue providing the altitude, even when there aren't enough satellites in view.

The question to me is why would someone want a faster Z.

Normally people only view their GPS in 2D, granted elevation could be useful for GPS speedos and the like, but when inside a car the barometer will lack precision.

The Private Pilot (ie n00b of t3h pilots!111!) in me knows that its incredibly unlikely to have issues seeing many GPS sats when flying, and I wouldn't ever want a static source that wasn't outside.

So I think this will be only a speed optomisation at most, however combined with GPS posistion and tempurature, such barometric data could no doubt be of use to weather forecasters who are trying to model incredibly localised patterns maybe?

No matter what your screen is showing you, you are currently occupying three dimensions of space, and if you want an accurate representation of that without already knowing at least your rough location, you need to lock on to more satellites than you do if you already know approximately how high you are.

At least, such is my limited understanding.

Also if I'm plummeting out of plane in the middle the night with no sense of position, then I'm not saying relying on my phone is a good idea but knowing when to pull my chute so I don't spend too much time in the stratosphere would be pretty handy.

I mean I'm not saying it's likely but...luck favors the prepared right?

As I said I support faster GPS (my last line in the post). I think it might be a faster, data light alternative to the A-GPS thing, but I can't really see it narrowing it down that much?

I'd have thought dual tuning GLONAS and GPS was better? After-all the error for these sensors will be vast depending on where you are. My understanding (may well have changed, I don't know) is that currently most work on one or the other, not both.

A reason I am saying this is I remember the first time I flew a plane in Asia after learning in mild weathered UK I was getting challanging readings from my static source. As such I'm not sure how well it would work as an optomisation.

I'm not saying its bad, I'm not saying it's not fun for geeks considering the no doubt low cost of this scale.

But I still don't see the need for faster Z, as most smartphone users are on the terraferma?

"The question to me is why would someone want a faster Z."

Cyclists, Joggers - anybody who uses their iPhone for logging external activities is frustrated with how inaccurate the iPhone is for capturing Z. It's not completely useless, but it's not very precise.

I bought one of the handle bar mounts for my phone and have really rather accurate Z, this is also in London too, AFAIK the software isn't using map data to help either, but surely that would be a good way of doing it too. Archway Hill has always been accurate, even on my old Garmin thing.

Again I think it is mostly for faster aqusistion, as i doubt how this will help anyone who isn't keeping their phone in a correct posistion for accurate sampling. These barometric sensors weren't that accurate 5-7 years ago when I played with them, I can't imagine them helping when in a pocket or waterproofed running strap / cycle case.

GPS coordinates are calculated off what are known as psudoranges: http://en.wikipedia.org/wiki/Pseudorange. You can imagine these 'ranges' as a calculated distance to a given satellite. Knowing the altitude ahead of time allows you to calculate your 3D position faster because you don't need as many range samples, or satellites, to do accurate estimates of position.

I think it only speeds up solving for position. Without an up to date local reference, the barometer can't tell you absolute altitude with any sort of precision.

I think the basic idea is that instead of dealing with the entire circle that you get from intersecting two spheres, you only have to deal with the parts of the circle that are remotely sensible according to the barometer.

GPS provides far better altitude data than a barometer. GPS altitude fixes are typically accurate to about 20m. An uncalibrated barometer can be off by 300m or more, depending on what the weather happens to be like at that particular moment.

I'm sure the barometer is useful for something, but providing better altitude data than GPS gives you is definitely Not It.

Edit: I should note that if you calibrate the barometer to the local atmospheric pressure, it can be extremely accurate, down to perhaps 3m or so, if it's a good barometer (like the one usually called an "altimeter" in an airplane). But it's not likely that a cheap phone barometer would achieve that, and of course you need some way to get the local base atmospheric pressure to begin with.

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