DATUM

Select a datum transformation

Platform:

OEM719, OEM729, OEM7500, OEM7600, OEM7700, OEM7720, PwrPak7, CPT7, CPT7700, SMART7, SMART2

This command is used to select the ellipsoid used for converting Cartesian co-ordinates to geodetic (latitude, longitude and height) and the transformation applied to positions calculated by the receiver before they are output.

The datum transformation selected by this command will be applied to all solutions calculated by the receiver. Solutions based on corrections, like RTK or pseudorange differential, will naturally be in the datum of the corrections; for example, RTK networks in North America will transmit corrections that position users in NAD83. Uncorrected solutions, meanwhile, will be in WGS84 or a datum closely-aligned to it. If different solutions are in different datums then a single transformation will not work in all cases. Care must therefore be taken when using this command.

With RTK, it is normally intended to position in the datum of the base station. A transformation applied to the natural solution will shift the solution out of the base station datum. Consequently, this command is generally not suitable for use with RTK.

Use of the factory default datum of WGS84 will result in no transformation being applied to any solution. User defined datums can also be used, after being created using the USERDATUM command or USEREXPDATUM command.

Datum transformations matter mostly for precise solutions like PPP and RTK, where the difference between datums is large relative to the solution accuracy. As already outlined, RTK solutions are, typically, already in the desired datum. Therefore, in most cases only PPP solutions will need transforming. To transform only the PPP solution, use the OUTPUTDATUM command.

Do not mix the DATUM USER and OUTPUTDATUM commands.

Message ID: 160

Abbreviated ASCII Syntax:

DATUM datum

Factory Default:

DATUM WGS84

ASCII Example:

DATUM USER

Field	Field Type	ASCII Value	Binary Value	Description	Format	Binary Bytes	Binary Offset
1	Command header	-	-	DATUM header This field contains the command name for abbreviated ASCII or the message header for ASCII (see page 1) or Binary (see page 1).	-	H	0
2	datum	WGS84	61	World Geodetic System 84	Enum	4	H
		USER	63	User defined datum set by the USERDATUM command and USEREXPDATUM command.