USEREXPDATUM
Set custom expanded datum
Platform: 
OEM719, OEM729, OEM7500, OEM7600, OEM7700, OEM7720, PwrPak7, CPT7, CPT7700, SMART7, SMART2 
This command permits entry of customized ellipsoid and datum transformation parameters. The command DATUM USER must be sent for the parameters set by USERDATUM to take effect.
Only a single set of USEREXPDATUM or USERDATUM entered parameters is valid at one time. Newer parameters entered by either command will overwrite previously entered parameters.
The transformation used by this command is the 7 parameter Helmert transformation, with the parameters provided being for the transformation from the user datum to WGS84:
Where:
X, Y, Z are the coordinates in the user datum
X_{s}, Y_{s}, Z_{s} are the coordinates in WGS84
T_{x}, T_{y}, T_{z} are the translation parameters corrected for translation rate (metres)
R_{x}, R_{y}, R_{z} are the rotation parameters corrected for rotation rate (radians)
s is the scale difference corrected for scale rate (unitless)
A given parameter P is corrected for rate:
P(t)=P(t_{r})+ Ṕ̇(t_{r}) (tt^{r})
Where:
t_{r} is the reference epoch of the parameters
t is the current epoch
P(t_{r}) is the parameter at the reference epoch
Ṕ̇̇(t_{r}) is the rate of the parameter at the reference epoch
The convention used by this command differs from that used by the DATUMTRANSFORMATION command, and from parameter conventions seen typically in transformation sources. Care should be taken that the parameter convention matches that in the equation above.
See the DATUM command for important guidance and details on datum operation.
Message ID: 783
Abbreviated ASCII Syntax:
USEREXPDATUM semi_major_axis flattening dx dy dz rx ry rz scale xvel yvel zvel xrvel yrvel zrvel scalevel epoch
Factory Default:
USEREXPDATUM 6378137.0 298.25722356280 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
ASCII Example:
USEREXPDATUM 6378137.000 298.25722356280 0.000000000 0.000000000 0.000000000 0.00000000 0.000000000 0.000000000 0.000000000 0.000000000 0.000000000 0.000000000 0.0000 0.000000000 0.000000000 0.000000000 0.000000000
Use the USEREXPDATUM command in a survey to fix the position with values from another known datum so that the GPS calculated positions are reported in the known datum rather than WGS84. For example, it is useful for places like Australia, where the continent is moving several centimetres a year relative to WGS84. With USEREXPDATUM, you can also input the velocity of the movement to account for drift over the years.
Field 
Field Type 
ASCII Value 
Binary Value 
Description 
Format 
Binary Bytes 
Binary Offset 
1 
Command header 
 
 
USEREXPDATUM 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 
semi_major_axis 
6300000.0  6400000.0 m 
Datum semimajor axis (a) (metres) 
Double 
8 
H 

3 
flattening 
290.0  305.0 
Reciprocal Flattening, 
Double 
8 
H+8 

4 
dx 
± 2000.0 m 
Translation values (metres) 
Double 
8 
H+16 

5 
dy 
± 2000.0 m 
Double 
8 
H+24 

6 
dz 
± 2000.0 m 
Double 
8 
H+32 

7 
rx 
± 10.0 radians 
Datum rotation angles A positive sign is for counter clockwise rotation and a negative sign is for clockwise rotation 
Double 
8 
H+40 

8 
ry 
± 10.0 radians 
Double 
8 
H+48 

9 
rz 
± 10.0 radians 
Double 
8 
H+56 

10 
scale 
± 10.0 ppm 
Scale value is the difference in ppm 
Double 
8 
H+64 

11 
xvel 
± 2000.0 m/yr 
Velocity vector along X‑axis 
Double 
8 
H+72 

12 
yvel 
± 2000.0 m/yr 
Velocity vector along Y‑axis 
Double 
8 
H+80 

13 
zvel 
± 2000.0 m/yr 
Velocity vector along Z‑axis 
Double 
8 
H+88 

14 
xrvel 
± 10.0 radians/yr 
Change in the rotation about X over time 
Double 
8 
H+96 

15 
yrvel 
± 10.0 radians/yr 
Change in the rotation about Y over time 
Double 
8 
H+104 

16 
zrvel 
± 10.0 radians/yr 
Change in the rotation about Z over time 
Double 
8 
H+112 

17 
scalevel 
± 10.0 ppm/yr 
Change in scale from WGS84 over time 
Double 
8 
H+120 

18 
epoch 
0.0 year 
Reference epoch of parameters (decimal year) Example: 2011.00 = Jan 1, 2011 2011.19 = Mar 11, 2011 
Double 
8 
H+128 