ZED-F9P - Integration manual
In practice, the relevant organizations choose to keep their respective frames very close to the
International Terrestrial Reference Frame (ITRF), defined and managed by the International Earth
Rotation and Reference Systems Service (IERS).
However, because the Earth's tectonic plates and even parts of the Earth's core move, new versions
of ITRF are defined every few years, generally with changes of the order of a few millimeters.
Consequently, the major GNSS occasionally decide that they need to update their reference frames
to be better aligned with the latest ITRF.
So, for example, GPS switched to WGS84 (G1150) in GPS week 1150 (early 2002) based on
ITRF2000, while GLONASS switched from PZ90.02 to PZ90.11 at the end of 2013, based on
ITRF2008. The net effect of this is that all the major GNSS use almost the same reference
frames, but there are some small (generally sub-centimeter) differences between them, and these
differences occasionally change.
In order to produce positions that can be shown on a map, it is necessary to translate between raw
coordinates (for example, x, y, z) and a position relative to the Earth's surface (for example, latitude,
longitude and altitude), and that requires defining the form of ellipsoid that best matches the shape
of the Earth.
Historically, many different ellipsoid definitions have been used for maps, many of which predate the
existence of GNSS and show quite significant differences, leading to discrepancies of as much as
100 meters in places. Fortunately, most digital maps now use the WGS84 ellipsoid, which is distinct
from the WGS84 coordinate system, but defined by the same body.
However, for RTK position accuracies now in the centimeter-level, the ITRF year for the WGS84
datum used by the mapping system must be known in order to transform the RTK rover position
into the correct reference frame.
The ZED-F9P stores the EGM96 geoid model with limited resolution, leading to degraded
accuracy of the reported mean sea level height and geoid separation. If the user application
needs higher geoid separation accuracy, it is required to apply its own adjustment to the
ellipsoidal height output from the ZED-F9P.
C RTK configuration procedures with u-center
This section provides some guidance when using u-center to configure base and rover operation.
C.1 Base configuration with u-center
This section describes setting a static base configuration in the u-center "Messages View" window.
Start u-center and connect to the ZED-F9P device. Under the UBX-CFG message tree, three
configuration messages are listed:
•
CFG-VALDEL
: Allows configuration deletion
•
CFG-VALGET
: Allows configuration reading
•
CFG-VALSET
: Allows configuration setting
All configuration item setting is done using the
UBX-CFG-VALSET
dialog. The general operation is
as follows:
1.
To open a configuration setting dialog, select
UBX-CFG-VALSET
in the message tree list.
2.
Select the required
Group
in the "Compose list entry" section.
3.
Select the associated key in the "Key name" pull-down menu.
4.
Once you have selected the configuration key, move it to the configuration changes list by
clicking
Add to List
.
UBX-18010802 - R08
Appendix
Page 96 of 110
Early production information