Hacker News Reader

Comment by bhartzer | Hacker News Reader

Barometer is very cool addition. I'm sure they'll eventually have an API for it.

may be i'm too introvert or just don't have the imagination - i'd more understand adding more sensors toward "tricorder", ie. ones that can say more about condition/health of the human host of the phone (temperature, heartbeat, alpha/beta/theta-waves, dopamine level, etc...)

What is it used for in the phone?

Elevation for fitness apps and environmental and weather(?) reporting.

Barometers are often used to improve motion tracking accuracy, not sure if this is a common use case for phones.

How is that helpful in motion tracking?

With sensor fusion you can improve the accuracy over just using GPS and accelerometers; it is quite common in quadcopters.

altitude is usually the least accurate position given by a GPS. A barometer helps you get closer, faster.

I have some MPX5100 pressure sensors connected up to an Arduino. When I first experimented with them, I was shocked to find that they were accurate enough to report pressure change simply from lifting the device off my desk and up to eye level.

Not that this says anything about the sensor used in the iPhone, but it's not unreasonable to expect that it could be used as some form of motion input.

It means instead of waiting for a GPS lock in 30 seconds it's under 10.

The barometer makes calculating your position via GPS much quicker, as it has an additional piece of data to simplify some of the maths it does.

Edit: here's a source which may confirm - http://pocketnow.com/android/google-confirms-barometer-inten...

Yeah, that doesn't make any sense. Barometers are only good for detecting relative altitude/elevation changes over short periods of time.

Over longer periods of time (hours/days) the atmosphere pressure is going to change whether you change altitude or not. Over short periods, the barometer can give a relative change. Without a known starting point, it can't give you absolute altitude/elevation.

It has nothing to do with getting a gps lock.

I'd be pretty surprised if the phones didn't pull down the satellite constellation data over the network vs waiting on the nav message broadcast from the satellites.

I think the elevation changes over short periods of time are essentials for the fitness apps.

Any decent smartphone can already get a GPS fix in a second or so.

The main bottleneck to a GPS fix these days is simply downloading the satellite positions. This is done over a 1970s-era protocol that operates at 50bps and takes about 30 seconds to transmit all of the data.

Smartphones bypass this by downloading the positions over their local data connection, which cuts that down to a fraction of a second.

Fixing your altitude to +/- 2000ft doesn't really help the process to any significant degree. If you have the satellite positions or can get them quickly, the rest comes fast. If you don't, you're doomed to be slow.

Huh, interesting. That's pretty cool to know. Thanks!

How much elevation are we talking about? Will it detect if I crouch and stand up, or you mean more geo-based elevation?

They are sensitive to altitude changes on the order of centimeters.

Thanks! That sounds amazing and quite useful.

Typically barometric altimeters are accurate to about 10s of feet.

Relative elevation tracking.

Reply on news.ycombinator.com