4 BASIC CONCEPTS
NOTICE
When the data are streamed via USB or
Ethernet,
fi
lter rate and frame rate have
to be matched. This is important as an inappropriate sample rate may lead to
oversampling or aliasing.
I
n the
PICO
SCALE
GU
I
, potential aliasing is indicated
by a small warning sign and the frame rate can easily be adapted to the
fi
lter.
NOTICE
When SmarAct
’
s motion controller MCS2 is connected, the
fi
lter rate is
fi
xed to
39.06 kHz to match the MCS2
’
s sample rate and thus to avoid aliasing.
4.7 Streaming aggregation
When data sources are streamed to the
PICO
SCALE
via USB or Ethernet, the
PICO
SCALE
usually
bundles a certain amount of data before it sends them. This so-called aggregation decreases the
communication overhead signi
fi
cantly.
I
f data are streamed with a speci
fi
c frame rate, the
PICO
-
SCALE
automatically uses a convenient aggregation size. This aggregation size is roughly set to
provide about 20 data packages per second. The protocol works most e
ffi
cient if the aggregation
size is a power of 2, i.e.
Aggregation
=
2
n
,
n
∈
N
However, if an external clock is used as frame rate, the
PICO
SCALE
cannot know the precise frame
rate and thus also an aggregation size cannot be estimated. The user has to set the desired aggre-
gation manually.
I
n the following table please
fi
nd an overview on the frame rates and respective
aggregation size the
PICO
SCALE
uses for direct streaming (i.e., an internal clock is used as frame
rate), which may serve as and rule-of-thumb to set the aggregation.
4.8 Network discovery protocol
The
PICO
SCALE
network discovery protocol enables to list all available
PICO
SCALE
s in your local
network. Within the
PICO
SCALE
GU
I
you may then easily select the appropriate device without
typing in the
I
P address after every startup of the
PICO
SCALE
or restart of the GU
I
. See chapter 7
for usage of the protocol with the GU
I
.
27
PicoScale User Manual
