2 Operation Details
2.4.6
Datum Transformation
By default the datum to which the coordinates refer depends on the positioning mode. For
standalone, PPP and SBAS positioning for example, the coordinates refer to a global datum:
WGS84 or ITRS. When using DGPS or RTK corrections from a DGPS/RTK provider, the coordi-
nates usually refer to a regional datum (e.g. ETRS89 in Europe).
Recent realisations of WGS84 and ITRS are closely aligned and the difference can be neglected
in most cases. The receiver considers them equivalent. However, regional datums may signif-
icantly differ from WGS84/ITRS, which may lead to coordinate jumps when switching between
different positioning modes.
2.4.6.1
Transformation to Regional Datum
It is possible to avoid this datum shift by configuring the receiver to transform all co-
ordinates to the regional datum used by the RTK base stations. This is done with the
command. The receiver knows the transformation parameters appli-
cable to the most common datums (e.g. ETRS89 or NAD83), but user datums can also be
defined with the
command.
Coordinates in the
and
SBF blocks refer to the datum se-
lected in
. The datum can be checked by decoding the
Datum
field of
these blocks.
2.4.6.2
Transformation to Local Datum
Sometimes it is needed to relate the coordinates to a local datum. Some RTK networks pro-
vide the necessary transformation and projection parameters as part of their RTCM stream,
in message types 1021 to 1027.
The local geodetic coordinates (latitude, longitude and height) are reported in the
SBF block, and the plane grid coordinates (easting, northing, height) are reported in the
SBF block.
The following conditions must be met for the receiver to provide local coordinates from the
information sent by the RTK network:
• the usage of RTCM v3.x MT1021-1027 must be enabled by the command
(these messages are enabled by default).
• the complete set of datum transformation messages must have been received from
the network. Plane grid coordinates are only available if the network supports one of
the messages in the 1025-1027 range. Otherwise, only the local latitude, longitude and
height are available.
• the position must be in the area of validity of the transformation parameters.
• to continue to get unbiased local coordinates when the positioning mode is not DGPS or
RTK, the network regional datum must be set with the
command.
See section 2.4.6.1.
65
Summary of Contents for PolaRx5TR
Page 1: ...PolaRx5TR Reference Guide Applicable to version 5 5 0 of the Firmware ...
Page 73: ...3 Command Line Reference Chapter 3 Command Line Reference 73 ...
Page 130: ...3 Command Line Reference COM1 gim CR R gim IonosphereModel off COM1 130 ...
Page 237: ...3 Command Line Reference COM1 237 ...
Page 279: ...3 Command Line Reference COM1 279 ...
Page 294: ...4 SBF Reference Chapter 4 SBF Reference 294 ...