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RTCM 10403.2

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 Marine – Hydrographic surveying, dredge operations, navigation in narrow

channels, buoy placement and auditing, even tidal height

 Air – Aerial surveying, landing system testing, calibration of other navigation

systems

 Land – Surveying, building and bridge construction, surface mining, agriculture,

road construction, asset location and management

It turns out that the RTK requirements for all these different applications don’t vary that

much. The broadcast link bandwidth and update rates are primarily determined by the

accuracy requirements and the signal blockage environment. Otherwise the required services

are similar for air, land and sea applications.

© RTCM – Not for reproduction or redistribution

RTCM 10403.2

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3 PRESENTATION LAYER

3.1 Introduction

3.1.1 Version 3 Database Architecture

Version 3 is written in a database format, loosely patterned after the NMEA 2000 standard.

Whereas the NMEA standard is written for a networked set of different electronic units, the

Differential GNSS Version 3 standard is written for a centralized distribution of data. For the

Version 3 broadcast, every bit counts in the frequently repeated messages, so while lining up on

byte boundaries is desirable, forcing each data field to occupy whole numbers of bytes is not

practical.

Also, the NMEA 2000 database has a wide disparity between Data Dictionary (DD) and Data

Field (DF) records. In the case of Version 3 broadcasts, there would be little difference. As a

consequence, rather than utilize both DF and DD tables, these are collapsed into one DF

definition. Rather than referring to “Parameter Groups”, this document will use the more

familiar term “Message Types”.

For messages whose lengths don't line up with byte boundaries, the reference station designer

should use zeros for undefined bits to fill out the last unfilled byte.

3.1.2 Message Groups

Message types contained in the current Version 3 standard (RTCM 10403.2) have been

structured in different groups. For proper operation of a particular service the provider needs to

transmit messages from each of several groups, as shown in Table 3.1-1. For example, to

provide RTK services the provider must transmit at least one message type from each of the

following groups: Observations, Station Coordinates, and Antenna Description. The different

message types in each group contain messages with similar information content.

In some cases the shorter ones contain the minimum needed to provide the service, while the

longer message types contain additional information for enhancing the performance of the

service. For example, Message Type 1001 contains the shortest version of a message for GPS

Observations, namely L1-only observables. For a broadcast link limited in throughput, use of

1001 might be appropriate. Message Type 1002 contains additional information that enhances

performance. If throughput is not limited and the additional information is available, it is

recommended to use the longer version of messages. Similarly Message Type 1003 provides

minimum data for L1/L2 operation, while Message Type 1004 provides the full data content.

The shorter observation messages save throughput, but contain less information. However, since

the additional information in the longer observation messages does not change very often, they

could be sent less often.

© RTCM – Not for reproduction or redistribution

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