This file defines the columns of data in the poseandtwist.log files produced
by the GRID software receiver. Each poseandtwist.log file contains
time-stamped precise relative pose solutions. ORT time stamps indicate the
time at which the position solution applies. See channel.txt for a definition
of ORT.

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Column        Quantity

1 ----------- ORT week number. 

2 ----------- ORT whole seconds of week.

3 ----------- ORT fractional second. 

4,5,6 ------- X,Y,Z position rW of the platform reference point (e.g., primary
              GNSS antenna's L1 phase center), in the W (ENU) frame in meters
              relative to reference antenna location.

7,8,9,10 ---- Quaternion qBW relating the body and local ENU frames.  Let qBW =
              [x,y,z,w] be the quaternion composed of these four elements in
              the order given.  Then vB = RBW*vW relates the expressions of the
              physical vector v in the world (W) and body (B) frames, where RBW
              is the direction cosine matrix corresponding to qBW.

11,12,13 ---- X,Y,Z velocity vW: the time rate of change of rW, in meters per
              second.
 
14,15,16 ---- X,Y,Z angular rate wB: angular rate of B relative to W, expressed
              in B in radians per second.

17,18,19 ---- X,Y,Z accelerometer bias baU expressed in the U (IMU) frame in
              meters/second^2.

20,21,22 ---- X,Y,Z rate gyro bias bgU expressed in U in rad/second.

23-40 ------- Diagonal elements of the error covariance matrix corresponding
              to the state vector [rW;e;vW,wB,baU,bgU], where e is the 3-by-1
              error state vector corresponding to the quaternion qBW.

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