[Ssc-dev] quick note on Carrie's work

[Harlo Holmes]

So far, it's worked this way:

When our user clicks the camera button, they're directed to InformaCam's
camera-management activity, which before launching the user's camera,
starts up our sensors and starts a log for those sensor readings.  Once
this log is created, and all the sensors have started up and are
successfully logging, the user is passed to their on-board camera app.  As
the user takes their photos/videos, each new media item is packaged with a
reference to the sensor log file for later.  FInally, when the user exits
the on-board camera activity, they're brought back to our custom activity
which shuts down the sensors, and seals the logs.

So, if a researcher wanted to gauge a user's movement as they took a photo
or video, that researcher already has several seconds of sensor data
captured before capture, during capture, and after capture; it's up to the
researcher (us?  j3m-scan!) to properly window that data.

As for resolution, currently, its resolution is not fine enough, as Hans
notes.  Accelerometer and gyroscope etc currently have a sample rate of
500ms.  However, this can be changed very easily because the rate at which
each sensor logs is set in a config file and it's a matter of changing that
long (and making sure we don't run into out-of-memory errors because of the
increased number of data points.)  I'm not too concerned about battery
life, though, because it's not as if the sensors are running continuously
as you use the app; this only happens while the user is making media, which
is a relatively short duration.  Also, the android sensor API is optimized
for gaming, so it should be fine for this minimal use case.

Thanks,
Harlo

++++++++++++++++++++++++++
Research Fellow, Head of Metadata
The Guardian Project <https://guardianproject.info>

pgp: 0xA4469630
twitter: @harlo


On Fri, Aug 23, 2013 at 4:42 PM, David Oliver <david at olivercoady.com> wrote:

> I think there's a technology side and a "user scenario" side to this - and
> I don't want this to be treated like an open-ended problem/issue.
>
> Here's the scenario I want to "solve": A photograph is a snapshot of a
> scene in time.  So, for photographs, we need the metadata to align with
> that moment in time.  I can imagine that most metadata we're tracking can
> also be "snapshotted".  BUT, with the accelerometer, the snapshot (single
> reading) is useless - you need more than one reading to show a
> delta/change.  While you could track accelerometer every 1/10 second, say,
> and then store readings in a circular queue (of, say, the last 10 seconds),
> that continuous reading would drain the device's battery.  But, to be
> valid, the readings have to be in the same timeframe as the photo.
>  So,.....open question.
>
> I suppose this is easier for video since you've got a start/stop time (and
> OS event, likely) allowing you to start/stop accelerometer capture.
>
> I think if we have geo-position, compass, and accelerometer then you make
> a nice graphic depiction of positionality and motion at time of capture.
>
> Dave
>
> David M. Oliver | david at olivercoady.com | http://olivercoady.com |
> http://dmo.tel | @davidmoliver | +1 970 368 2366
>
>
> On Fri, Aug 23, 2013 at 3:09 PM, Nathan of Guardian <
> nathan at guardianproject.info> wrote:
>
>> Adding Harlo to this thread, and cc'ing the list, as this is an
>> important general topic.
>>
>> On 08/23/2013 03:06 PM, David Oliver wrote:
>> > Here's one thing I want to know to aid in this process:  As I understand
>> > it, having a single accelerometer reading is useless for determining
>> > anything about movement, it is the comparative readings that are
>> important.
>> >  Using, say, 3 readings, you could assert something about motion.  But,
>> > InformaCam does not know "I should collect an accelerometer reading just
>> > before the picture is taken, then one during, then one after - since it
>> > does not know when media is created.  Yet, you can't possibly gather
>> > accelerometer (and/or compass) in real time all the time and then wait
>> to
>> > use it.......so what does InformaCam actually do?
>> The question is then, how/when are we logging accelerometer data, and
>> what can or should we infer from it?
>>
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