Recommended Alignment Procedures

NovAtel offers different alignment methods depending on the type of IMU used and the end user's application.  By default, high grade IMUs are able to perform a static alignment, and lower grade IMUs require a kinematic alignment.  In a simplistic way, high grade IMUs can be defined as having a gyro bias of lower than 15 degrees per hour (Earth's rotation rate), and low grade IMUs as having a gyro bias of greater than 15 degrees per hour.

Users can also enter their initial azimuth or full attitude values for a manual alignment.  This can be done for any IMUs.  This method is only recommended if the azimuth or attitude values are accurately known.  Entering an erroneous initial azimuth or attitude values will lead to real-time performance errors.

A video describing the above alignment methods can be found here:

http://support.novatel.com/entries/315958-basic-span-setup-and-alignment

Customers can have the additional option of using NovAtel's ALIGN technology to perform an aided alignment.  This requires a SPAN setup with two receivers and two antennas.  This dual antenna setup provides distance and bearing information between a “master” and “rover”.  Azimuth calculated from ALIGN is then used to initialize alignment.  Align aided alignment starts only after the primary and secondary lever arm information is entered using the commands SETIMUTOANTOFFSET and SETIMUTOANTOFFSET2.

There are two types of alignment using NovAtel's ALIGN technology:

Aided Transfer: This is the default alignment procedure for all dual antenna SPAN setup.  If your vehicle is not stationary during the alignment, such as on a ship, the Aided Transfer Alignment is the alignment routine to use. This is the default alignment for SPAN-SE-D, so the configuration is relatively simple. The aided transfer alignment method uses the ALIGN baseline solution to perform an instantaneous alignment of the INS (Inertial Navigation System).

No additional configuration is required for this alignment routine. The alignment will happen instantaneously once the receiver establishes communication with the IMU and computes a fixed integer, verified ALIGN solution. The INS status will remain in INS_ALIGNING mode until the aided transfer is complete and INS status changes to INS_SOLUTION_GOOD.

Aided Static: This mode will perform a standard static alignment routine given an initial azimuth value calculated from ALIGN.  It is recommended for vehicles where the initial roll is more than 20 degrees and the vehicle can stay stationary for the duration of the alignment process.  The user must initiate this alignment technique by sending in the command:

ALIGNMENTMODE AIDED_STATIC

Below is a summary of what alignment methods are available for which IMU:

IMU

Category

Alignment Options

OEMV

SPAN-MPPC

SPAN-SE

HG1700, LN200, FSAS, uIRS, HG1900

High Grade

 

 

Stationary

YES

YES

YES

Kinematic

YES

YES

YES

ALIGN Transfer***

NO

YES*

YES**

HG1930,LM20,
CPT

Lower Grade

 

 

Stationary

NO

NO

NO

Kinematic

YES

YES

YES

ALIGN Transfer***

YES****

YES*

YES**


*- requires ALIGN remote receiver (-Z) model
 

**- requires SPAN-SE-D-xx-Z receiver

***- ALIGN Transfer requires ALIGN remote to interface with the main SPAN receiver supplying Heading aiding information.

****- ALIGN is only available for OEMV in the SPAN-CPT platform