Spectra Precision ProMark 800 Reference Manual - Manual (Page 73)

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Precise Surveying - Field Applications & Concepts
Using a Virtual Antenna
What is the
Problem?
Not all the GNSS antennas available on the market are known
to all hardware manufacturers and software editors.
Now, when post-processing raw data files, this is a problem
because these files hold the names of the GNSS antennas
that were used for data collection. From these names, the
software is supposed to retrieve the essential dimensional
parameters of these antennas (phase center offsets, SHMP
offset, radius, ARP). These dimensions are essential if you
want the post-processing to deliver the best possible accuracy
for all your points.
Something goes wrong in the post-processing when the
header of a raw data file refers to what is an unknown antenna
name for your software.
And what if instead, a universal antenna name was
mentioned in the file that would prevent your software from
being stalled? That’s where the concept of virtual antenna
comes into play. A virtual antenna is an antenna whose
characteristics are known to a maximum of actors in the
surveying community
So the purpose of substituting the name of the real antenna
for the name of a virtual antenna is to make sure the raw data
file will always be recognizable and “processable”, whatever
the post-processing software used. Using a virtual antenna is
like making your raw data files virtually “universal”, by
disconnecting them from the surveying equipment that
collected them.
But this is no minor change for the receiver, as explained
below.
What the Receiver
Has to Do to
Support a Virtual
Antenna
Using a virtual antenna means moving the spatial point for
which data collection actually takes place from the real
antenna phase center to the virtual antenna phase center
(and there are as many phase centers as there are frequencies
that the antenna can receive).
The diagram below shows an example of real and virtual
phase centers for one of these frequencies.