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Evidence of iPhone 6 Atmospheric Pressure Sensor Found in iOS 8
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Mad Mac Maniac
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If this is accurate this would be cool for tracking run/hike/biking apps to show you when you were on an incline/decline.
If this is the expectation from a barometer, then it is highly unrealistic. You can't forecast weather using barometric pressure changes alone. It is also not true that you need to have an "official" weather station nearby to get a reasonable forecast. At least in the U.S., the NWS provides forecasts localized for any point in the country.
But you can enough to report on it. There's nothing in the code snippet about a barometer or barometric pressure. The name of the article is "Evidence..." There's no evidence there.
What that it was so simple. All altitude measurements are abstractions and are determined based on a model. The GPS model makes an assumption about the shape of the earth. Navigation and mapping uses the MSL (mean sea level) model, which is very different. In aviation, MSL is adjusted for barometric pressure (pressure altitude). Pressure altitude and GPS altitude hardly ever agree.
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The concept of "accuracy" effectively doesn't exist, only differences in the way altitude is measured. One is not more "accurate" than other other, only different.
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This may be so, but a barometer isn't really needed for this to be accomplished. GPS would probably be much better for this task, as it is based on a steady-state earth model. Barometric pressure is constantly changing and will behave even less predictably inside of a building that is at least partially sealed from outside air pressure.
As far as business people go it could be very useful if the transducer is accurate. For example every farmer that I've ever known has had a barometer at his residence.
The real question is, is this a barometer or rather just processed GPS data. You probably can get better altitude information from GPS these days.
Not really. Barometric pressure doesn't tell you as much as you might imagine, and having a barometric reading for your current location doesn't tell you anything that you can't find already, plus a whole lot more. Like I said, for the U.S. at least, the NWS can supply amazingly localized hourly forecasts. A really useful thing would be an app that retrieved this information from the NWS model for your current coordinates. This would be far, far more useful than barometric pressure. I've attached one of these forecasts so you can see what I am talking about.
Attachments
The sensors used in smartphones and tablets are able to recognize altitude changes as little as two feet.
GPS doesn't work inside most buildings.
Short term relative pressure changes, instigated by accelerometer events, allow figuring out relative height changes. (You're thinking too long term.)
Note that the API they found is called "isRelativeAltitudeAvailable", and triggers on changes... not absolute values.
That's why the scenario I gave was that you enter on the ground floor. From that point, relative changes during movement are all you need.
Related to that, there's an Android app, part of PressureNet , that collects readings to be used by scientists. No doubt iOS devices will be added to this if they get a sensor.
Good point about GPS in buildings. But... you will need more data than what you suggest to measure altitude change by any method.
Let's say for discussion purposes that your device already has a reference altitude for ground floor level in a given building (not an easy thing necessarily, but just for discussion). You enter the elevator and push "10." How does your device know when you step out that you are on the 10th floor? Before you say, "because it measures your relative change in altitude," consider that floor height in buildings is not standardized, and you'd only have to be off by ±1 foot for the device to think you are on the 9th or 11th floors. Once you told the device that you were on the 10th floor, it could then interpolate the floors in between -- maybe. Even this assumes no tall lobby spaces, mezzanines, and the like.
This is hairy stuff. Without being supplied with a whole lot of accurate crowd-sourced data, it has little chance of being useful.
GPS doesn't work indoors unless one is close to a window. My company is currently working with iBeacon. A combination of technologies would be the best: wifi, iBeacon micro location and atmospheric pressure.
edit: Sorry, never mind. KDarling was faster than I was.
Or, not. If you read past the Google pitch, you will find that the data has to date not been shared with anyone, and that the concept of this data improving weather forecasting is currently just a theory.
Yes, crowd sourcing will be important to figuring out the distance between floors. But that won't take long, once there's a lot of these in place.
True, it might have to ask users in new locations to confirm the floor. (Which of course, will then be part of crowd sourcing.)
Apple has bought a fair bit of indoor locating tech over the past couple of years. Unlike Google, they would find a way to leverage all their devices.
We shall see. I'm a skeptic when it comes to crowd sourcing. Not only can't everyone be bothered to report, they aren't necessarily reporting accurately when they do. If you've ever tried to use GasBuddy you know what I mean, and they incentivize reporting.
Fair enough. I could be giving Apple too much credit.
My main thrust was to point out that we don't need to know the local pressure altitude (although, sure, that info could be used for calibration as well). Quick relative changes while moving up or down can be useful.
-- Pilot trivia
I wonder if everyone working on this kind of thing, realizes that the aircraft altimeter setting put out by the NWS/NOAA is offset by ten feet ?
E.g. at sea level (0 feet) and standard pressure of 29.92", the official altimeter setting will be... 29.91 !
The reason for this, is that a DC-3's altimeter static opening was 10' off the ground. Dropping 0.01" compensates for that, so the DC-3's altimeter showed 0 feet with its wheels sitting on the ground.
A much shorter Cessna 172 with a static opening about 4' off the ground, should therefore show an elevation about six feet under the runway - grin - although I don't think anyone's really noticed that.
(I used to design slide rule flight computers for fun, and have an extensive collection of them and early air navigation texts.)
I would. It would also make the phone its own weather station with pressure drops/rises.
I remember now from some previous discussions that you are also a pilot.
No, I was not aware of the offset. That's good stuff. I will try it out on some of my grizzled veteran pilot friends and see if they are aware of this. All these years we've been doing it wrong. I can now blame all of my worst landings on this terrible hidden discrepancy.
Speak of static ports, the average GA aircraft is about as airtight as a log cabin. Yet, the static port is located outside of the aircraft, presumably because it would not be as accurate if the source was inside. (I had an alternate static air source inside on my old C-172, but I never compared it to the outside port.)
Anyway, the point such as it is: measuring barometric pressure inside a building seems like a pretty dicey affair, especially a modern building without opening windows and an aggressive HVAC system. So I am thinking, anyway.
And if you need any more E-6Bs...
I love comments like these because they illustrate how sad some of these peoples' lives are that they jump at any opportunity to embarrass and insult somebody who doesn't have the opportunity to slug them one.
Wow, if you've got a reference for that, I'd be keen to do some further reading. The ability to detect a one metre elevation change near sea level implies a resolution of about 10Pa, which I consider to be very impressive.
I presume slower changes (e.g. typical 100Pa changes over the course of a day) would be easy to filter, and ignore, but I wonder how it'll deal with mistakes such as when it thinks you've changed floors just because the wind changed direction, which could easily have a 40Pa+ effect on local pressure (e.g. see here).
Indoor mapping
At WWDC the introduced indoor mapping... These are some of the api for that.. Currently the building has to be mapped be fore this feature will work...
There are many other ways to get altitude outside of a barometer and they would be fairly ineffective for indoor use.
At WWDC the introduced indoor mapping... These are some of the api for that.. Currently the building has to be mapped be fore this feature will work...
There are many other ways to get altitude outside of a barometer and they would be fairly ineffective for indoor use.