Acutime 2000 Synchronization Kit User Guide A-87
ATrimble Standard Interface Protocol
0x8E-14
Command Packet 8E-14

Set New Datum

This packet allows the user to change the default datum from
WGS-84 to one of 180 selected datums or to a user-entered custom
datum. 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 Altitu de (LLA). This will affect
all calculations of LLA in packets 4A and 84 and 8F-AC and 8F-0B.
The receiver responds with packet 8F-14.
The user may want to change the datum to match coordinates with
some other system (usually a map). Most maps are marked with the
datum used and in the US the most popular datum for maps is
NAD-27. The user may also want to use a datum that is more
optimized for the local shape of the earth in that area. However, these
optimized datums are truly "local" and will provide very different
results when used outside of the area for which they were intended.
WGS-84 is an excellent general ellipsoid valid around the world.
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 datum desired. For a list of the datums and their indexes, see
TableA-101.
Table A-71 Command Packet 8E-14
Byte # Type Value
0 Superpacket ID 0x14
1-2 INTEGER Datum index