

The Galaxy S4 has a Barometer - cryptoz
http://www.cumulonimbus.ca/the-galaxy-s4-has-a-barometer/

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KaeseEs
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.

~~~
maxerickson
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.

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jbuzbee
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.

~~~
jeza
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.

~~~
kybernetyk
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.

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lucb1e
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).

~~~
andrewaylett
Yes, the S3 has one too.

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calinet6
_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...](https://play.google.com/store/apps/details?id=ca.cumulonimbus.barometernetwork&hl=en)

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Tyrannosaurs
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.

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trendspotter
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.

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

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dan1234
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?

~~~
dbaupp
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).

~~~
voltagex_
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.

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huherto
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>

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jusben1369
Does this help running/cycling apps where folks want to measure altitude gains
more efficiently?

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ChuckMcM
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 :-)

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

~~~
lucb1e
I knew; I just didn't know what to do with it.

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klinquist
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 :).

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37prime
Does Galaxy S4 have a kitchen sink?

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criley
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...](https://play.google.com/store/apps/details?id=ca.cumulonimbus.barometernetwork&hl=en)

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!

~~~
cjg_
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.

~~~
diroussel
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...](http://gis.stackexchange.com/questions/12866/why-does-gps-positioning-
require-four-satellites)

~~~
StavrosK
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.

~~~
Retric
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.

~~~
correctifier
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...](http://en.wikipedia.org/wiki/List_of_devices_with_Assisted_GPS)

