

Show HN: Open source Android app building a network of barometers - cryptoz
https://market.android.com/details?id=ca.cumulonimbus.barometernetwork&1.3.2

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Thrymr
Cool idea. A couple questions I have about it:

Are graphs available on the website? (I tried clicking through to
cumulonimbus.ca but it was not loading.)

Does it account for elevation? A change of elevation of 100 m is about 12 mbar
of pressure, comparable to a modest weather event. You could use ground
topography to correct, but people working in midtown Manhattan skyscrapers
would be a noisy signal, for example.

~~~
cryptoz
Currently the data isn't available outside the app, but I'm working on that
and should have that out within a couple of weeks. My focus so far has been
growing the user base, so the web interface has lagged. Coming soon!

For elevation, we currently attempt no fixes. The attitude I've held so far
has been that this is the primary reason for building a _network_, since a
single barometer cannot be trusted. However, your Manhattan scenario is
interesting: what if most people are constantly changing elevation? Hm. I'll
work on that one...

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law
This is a wonderful idea, especially since the area covered by cell phones
vastly surpasses that of weather stations. Unfortunately, there's a very real
privacy concern of which you must remain cognizant: storing a time series of
the paired barometer reading and GPS coordinates. This information is
personally identifiable, even if the device ID is just a unique string of
numbers.

I'm not sure how you're storing the data, but I would suggest to store _only_
the GPS coordinates and barometer reading, normalizing both to have the same
approximation error.

~~~
cryptoz
> Unfortunately, there's a very real privacy concern of which you must remain
> cognizant: storing a time series of the paired barometer reading and GPS
> coordinates. This information is personally identifiable, even if the device
> ID is just a unique string of numbers.

Yes, this has been a complication from the start. Here's our current
policy/methods: We delete all data after 1 month and we let users remove all
of their submitted data completely. We never show anyone's actual location on
the map (coordinates are fudged by a few hundred meters).

I do want to store some data longer than 1 month in the future as will be
helpful to use for data mining, looking for patterns, etc. But first I will
have to find a way to carefully anonymize it.

~~~
law
I'd surprisingly prefer storing all data indefinitely and _not_ allowing users
to delete what they submitted if and only if you _also_ eliminate any way to
group locations by a device.

This data is just too dangerous, even in spite of innocuous intentions. Data
breaches happen, National Security Letters remain threats, and targeting ads
based on a user's current location will tempt anyone. You will fill your users
with confidence if you remove your ability to group the data points.

Moreover, you shouldn't discount the importance of historical barometric data.
At some point, it might no longer be practical to store the data in its most
atomic state, but maybe rolled up to a periodic snapshot (maybe hourly) of
some geographic region.

What data would you be looking to store for longer than a month?

------
cryptoz
I'm the developer for this project. Currently only the Motorola Xoom and the
Galaxy Nexus can submit readings, but all devices 3.1+ can download the app.
Let me know what you think, any comments, suggestions, etc.

In the long run, we're working towards improving short-term, local weather
prediction by adding this new pool of unprecedented data to the mix.

Edit: Source available at <http://cumulonimbus.ca>

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nix
More data is nice, but the experience with citizen-operated weather stations
suggests that the data is useless without extensive quality control.
Calibration is hard, and mobile sensors are particularly challenging. What
happens when one of the sensors goes into a climate-controlled building, then
takes an elevator to the 30th floor?

~~~
cryptoz
So, part of this is an experiment. I don't think anybody's done such fast and
distributed crowdsourcing of weather data before, so I'm not sure how useful
the data will end up being. As far as a single user entering a building,
taking elevators, etc, I'm not concerned since those data points will stand
out from the nearby readings and can easily be discarded. However, a point
raised in another comment here is, what if most users in an area (say
Manhattan) are constantly changing elevation. That very well may pose a
problem. We'll see. :)

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juliano_q
Thats great, surprisingly there are already a few submissions in my area (São
Paulo / BR) even if the Galaxy Nexus was not launched here yet and the only
device with a barometer is the Xoom. I think it is a revolutionary idea that
can change the way we see weather forecasts and I am really excited about it.

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untog
This is a very cool idea. Sadly I don't have a Galaxy Nexus in order to
participate (just bought a Galaxy S2, wondering if I will regret that choice)
but I can't wait to see how this kind of thing turns out in a year or two when
a ton of people have these devices.

~~~
viraptor
Slightly offtopic - have you noticed anything lacking in GS2, compared to what
newer handsets have? I was going to do the same and can't find anything apart
from raw processing power that I'd miss.

~~~
untog
Not really. I actually came from having tried a Windows Phone (Samsung Focus
S) for nearly a month which was incredibly light and thin, so the GS2 actually
feels quite bulky to me- the 4.5" screen is honestly a little too big for my
liking, but given that the Galaxy Nexus is bigger still I don't see any very
viable alternatives.

Another thing to note is that the AT&T SG2 (the one I have, the 'Skyrocket'
LTE version) is very new, and really don't have any fully functional custom
ROMs yet. I'm using a half-baked CyanogenMod version and there are still
plenty of issues.

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jpablo
Slightly off topic: But why does those phones have barometers build in? What
are those normally used for?

~~~
ryandvm
The altitude input helps speed up the GPS lock process.

[http://androidcommunity.com/samsung-galaxy-nexus-
barometer-i...](http://androidcommunity.com/samsung-galaxy-nexus-barometer-is-
for-faster-gps-lock-20111020/)

------
patrickod
Is there any page that displays aggregate data without having to install the
app?

~~~
cryptoz
Not yet, but I'm working on it! So far every line of code I've written has
been in effort to directly increase barometer reading submissions. That's
coming along nicely, so one of our next steps is to redo the website and
include a map and graphs of the data there as well.

