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Copernicus GPS Receiver 165
TRIMBLE STANDARD INTERFACE PROTOCOL (TSIP) A
TSIP Superpackets
Several packets have been added to the core TSIP protocol to provide additional
capability for OEM receivers. In OEM Packets
0x8E and their 0x8F responses, the
first data byte is a sub-code which indicates the superpacket type. For example, in
Packet
0x8E-15, 15 is the sub-code that indicates the superpacket type. Therefore the
ID code for OEM packets is 2 bytes long followed by the data. Command packet
0x35 is used to enable superpackets.
Command Packet 8E-15 - Set/Request Datum
This packet allows the user to change the default datum from WGS-84 to one of 180
selected datums. The datum is a set of 5 parameters which describe an ellipsoid to
convert the GPS receiver’s internal coordinate system of XYZ ECEF into Latitude,
Longitude, and Altitude (LLA). This affects all calculations of LLA in packets 0x4A
and 0x84.
The datum can be changed to match coordinates with another system such as a map.
Most maps are marked with the datum used. In the US, the most popular datum for
maps is NAD-27. You may choose a datum optimized for the local shape of the earth,
however optimized datums are truly local and provide very different results when
used outside of the area for which they are intended. WGS-84 is an excellent general
ellipsoid valid around the world. To request the current datum setting, one data byte is
sent. Report Packet 0x8F is returned.
Table A.56 Command Packet 8E-15
To change to one of the internally held datums, the packet must contain exactly 2
bytes representing the integer value of the index of the desired datum.
Table A.57 Command Packet 8E-15
Note – To request the current datum, send Packet 8E015 with no data bytes.
Byte Type Meaning
0 Superpacket 0x15
Byte Type Meaning
0 Superpacket ID 0x15
1-2 INT16 Datum index