IMR File
Waypoint converts all custom IMU raw binary formats into a generic format (IMR), which is read from Inertial Explorer following the decoding process in IMU Data Converter. See Raw IMU Data Converter for more details.
Because it contains vital information for reading and decoding the data, the first 512 bytes of the generic IMU data format is a header which must be filled in, read and interpreted. In a C/C++ structure definition, the generic format header has the following fields:
|
Word |
Size (bytes) |
Type |
Description |
|---|---|---|---|
|
szHeader |
8 |
char[8] |
“$IMURAW\0” – NULL terminated ASCII string |
|
bIsIntelOrMotorola |
1 |
int8_t |
0 = Intel (Little Endian), default 1 = Motorola (Big Endian) |
|
dVersionNumber |
8 |
double |
Inertial Explorer program version number (e.g. 8.80) |
|
bDeltaTheta |
4 |
int32_t |
0 = Data to follow will be read as scaled angular rates 1 = (default), data to follow will be read as delta thetas, meaning angular increments (i.e. scale and multiply by dDataRateHz to get degrees/second) |
|
bDeltaVelocity |
4 |
int32_t |
0 = Data to follow will be read as scaled accelerations 1 = (default), data to follow will be read as delta velocities, meaning velocity increments (i.e. scale and multiply by dDataRateHz to get m/s2) |
|
dDataRateHz |
8 |
double |
The data rate of the IMU in Hz. e.g. 0.01 second data rate is 100 Hz |
|
dGyroScaleFactor |
8 |
double |
If bDeltaTheta == 0, multiply the gyro measurements by this to get degrees/second If bDeltaTheta == 1, multiply the gyro measurements by this to get degrees, then multiply by dDataRateHz to get degrees/second |
|
dAccelScaleFactor |
8 |
double |
If bDeltaVelocity == 0, multiply the accel measurements by this to get m/s2 If bDeltaVelocity == 1, multiply the accel measurements by this to get m/s, then multiply by dDataRateHz to get m/s2 |
|
iUtcOrGpsTime |
4 |
int32_t |
Defines the time tags as GPS or UTC seconds of the week 0 = Unknown, will default to GPS 1 = Time tags are UTC seconds of week 2 = Time tags are GPS seconds of week |
|
iRcvTimeOrCorrTime |
4 |
int32_t |
Defines whether the time tags are on the nominal top of the second or are corrected for receiver time bias 0 = Unknown, will default to corrected time 1 = Time tags are top of the second 2 = Time tags are corrected for receiver clock bias |
|
dTimeTagBias |
8 |
double |
If you have a known bias between your GPS and IMU time tags enter it here |
|
szImuName |
32 |
char[32] |
Name of the IMU being used |
|
reserved1 |
4 |
uint8_t[4] |
Reserved for future use |
|
szProgramName |
32 |
char[32] |
Name of calling program |
|
tCreate |
12 |
time_type |
Creation time of file |
|
bLeverArmValid |
1 |
bool |
True if lever arms from IMU to primary GNSS antenna are stored in this header |
|
lXoffset |
4 |
int32_t |
X value of the lever arm, in millimeters |
|
lYoffset |
4 |
int32_t |
Y value of the lever arm, in millimeters |
|
lZoffset |
4 |
int32_t |
Z value of the lever arm, in millimeters |
|
Reserved[354] |
354 |
int8_t[354] |
Reserved for future use |
The single header, which is a total of 512 bytes long, is followed by a structure of the following type for each IMU measurement epoch:
|
Word |
Size |
Type |
Description |
|---|---|---|---|
|
Time |
8 |
double |
Time of the current measurement |
|
gx |
4 |
int32_t |
Scaled gyro measurement about the IMU X-axis |
|
gy |
4 |
int32_t |
Scaled gyro measurement about the IMU Y-axis |
|
gz |
4 |
int32_t |
Scaled gyro measurement about the IMU Z-axis |
|
ax |
4 |
int32_t |
Scaled accel measurement about the IMU X-axis |
|
ay |
4 |
int32_t |
Scaled accel measurement about the IMU Y-axis |
|
az |
4 |
int32_t |
Scaled accel measurement about the IMU Z-axis |
The angular increments (or angular rates) are signed integers. The scale factor to obtain a double precision word must be supplied by the dGyroScaleFactor variable in the IMR header. Similarly, the accelerations (or velocity increments) are signed integers and must be scaled by the dAccelScaleFactor variable in the IMR header.