[evaal contest] 2 Hz update requirement and coordinate system

[Francesco Potortì]

Dear competitors,

some clarifications on the topics in the subject.

The technical annex mentions a "suggested frequency of 2 Hz" for sending
data to the measurement app.  As stated, this is in fact a suggestion:
there is no hard requirement on the updating rate.  A frequency that is
too high may in principle slow down the measurement application, and
indirectly harm the precision of your app.  A frequency that is too low
may be the cause of a bigger estimation error, as estimates are done
when the actor presses the button, and they will refer to the last
position received by the app before the button is pressed.

Coordinates will need to be in the coordinate systems that we will
indicate.  At the moment, the obvious candidate is WGS84 (latitude
and longitude) for x, y, and the number of floor (an integer starting
from 0) for z.  The timestamp should be in milliseconds from the epoch,
retrieved from currentTimeMillis().

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