[evaal contest] a clarification about timings

[Francesco Potortì]

Dear competitors,

in the technical annex we say that "each localization system should
produce localization data with a frequency of 1 new item of data every
half a second (this will be also used to evaluate availability)".

This provision is intended to measure the capability of your
localization system to provid up-to-date info, that is, to work in real
time.  The timings considered will be those when your system calls the
Activator.locate method.

If your system internally generates readings at the correct timings, but
is late in calling the Activator.locate method, then the availability
score may be lowered, as some samples will be discarded.  For example,
if your system generates samples # 0, 1, 2, 3, 4 at times (ms) 0, 500,
1000, 1500, 2000 and calls the Activator.locate method at times 0, 500,
1980, 1990, 2000, then samples # 2, 3 will be considered as missing, and
the two last readings will be discarded (considered invalid).  Accuracy
will be computed based on the valid samples only.  So you may get
a high score on accuracy, but you will get 60% score on availability.

If your system internally generates reading once per second, but calls
the Activator.locate method at the correct timings by providing the same
sample twice, you will get 100% score on availability, and a lower score
on accuracy (because one sample in two is equal to the previous one).

-- 
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