RTCM is a
streaming service for transmitting
differential GPS corrections. It is based on the RTCM SC-104
specification which was originated by a committee of the RTCM (Radio
Technical Commission for Maritime Services).
The RTCM streaming service is available on serial ports, TCP ports and
UDP ports. The NetRS can act as an RTCM reference station for many
different applications, using a variety of RTCM SC-104 versions and
styles. There are two basic configuration options:
-
Version
There have been several versions of the RTCM standard. The
formatting for many record types changed in each version. It is
necessary that any Rover that uses the corrections be set to expect
the same version as the reference station. See the information
below for a description of the versions supported by the NetRS.
-
Style
The RTCM standards include a variety of record formats that can be
used for many different type of applications. The exact combination
of records depends on the specific application. The NetRS provides
a choice of three pre-configured styles. Or you can select a
Custom style that includes the record types of your choosing.
The details of the pre-configured styles are listed below.
Note that some record types are not available with some of the
supported RTCM versions.
RTCM Versions
-
Version 2.1 - Defined in 1993 and introduced message types 18 and
19, which were required to support PDGPS applications that provide
centimeter accuracy through carrier phase solutions. The full
content of RTCM 2.0 was retained in RTCM 2.1. The USCG 9-3 option
was also adopted as a part of this version.
-
Version 2.2 - Defined in 1998 and supported measurements from the
Russian GLONASS satellites. This required changes to message types
18 and 19, which are not fully compatible with RTCM 2.1.
NOTE: Do not combine RTCM 2.1 and 2.2 at the base and at the rovers.
-
Version 2.3 - Defined in 2001 and includes the definition of message
type 23 to identify antenna types, and message type 24 to define
information about the antenna reference point. The description of
message types 18-21 was also clarified to provide better
compatibility between implementations by different manufacturers.
Styles
The messages that are streamed out the selected port are determined by
the selection of the version and the style. These messages vary
depending on whether the application is:
- DGPS
- RTK
- DGPS and RTK
- Custom application
When a Custom style is chosen, the web-browser interface will show
a set of checkboxes that allow selection of specific message types.
For the preconfigured styles the enabled messages are dependent on
the RTCM version, as listed below:
-
Version 2.1
- DGPS: 1, 3, 22, 59
- RTK: 3, 18, 19, 22, 59
- DGPS+RTK: 1, 3, 18, 19, 22, 59
-
Version 2.2
- DGPS: 1, 3, 22, 59
- RTK: 3, 18, 19, 22, 59
- DGPS+RTK: 1, 3, 18, 19, 22, 59
-
Version 2.3
- DGPS: 1, 3, 22, 24 59
- RTK: 3, 18, 19, 23, 24
- DGPS+RTK: 1, 3, 18, 19, 22, 23, 24, 59
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