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APN-068 Rev C
MEMS IMUs are typically used in backpack systems due to their small size and low power
consumption. The following guidelines will help ensure the success of both SPAN’s real time
solution and Inertial Explorer’s post-processed solution in these applications:
It is important to start and finish the survey walking in an area with reasonably open views of
the sky. We recommend that at least 30 to 40 seconds of data be collected while walking at
a more or less constant heading. This will ensure that an initial position, velocity and
heading can be determined from the GNSS data, which is required by the alignment
process. Collecting stationary data is unimportant as MEMS IMU’s are incapable of static
Following this initial coarse alignment procedure, several changes in heading (left and right
turns) should be observed to maximize attitude convergence prior to entering challenging
GNSS conditions. Collecting stationary data during the alignment is unimportant as MEMS
IMU’s are incapable of static alignment.
If an alignment can be achieved in real time, it is a good indication that post-processing will
also be successful in the forward processing direction. In order to achieve an alignment in
real time in a pedestrian application, it is recommended to lower the alignment velocity
threshold to the minimum value of 1.15 m/s. This can be done through the
Pedestrian processing profiles are presently included in Inertial Explorer 8.60 for
ADIS16488, STIM300, CPT, KVH1750 and FSAS SPAN systems. If the data has been
decoded in 8.60.5025 or later, Inertial Explorer will attempt to automatically detect
“Pedestrian” as the processing environment and thus automatically load the appropriate
pedestrian profile when accessing the tightly coupled processing dialogue.
If you do not see a pedestrian profile for your system under the processing dialogue, please
or edit the automated alignment thresholds manually to apply
a minimum velocity of 0.5 m/s and a heading SD tolerance of 45 degrees. These are
currently the default alignment tolerances for all pedestrian applications within Inertial
To maximize solution accuracy and for quality analysis, Inertial Explorer
processes data in
the forward and reverse directions. Thus achieving an alignment in the reverse direction
which is equally important as the forward direction. As such, the above alignment guidelines
are equally applicable to reverse processing, and the same field procedures used to start
the survey should be repeated at the end.
For best results in Inertial Explorer, process tightly coupled and choose the “multi-pass”
processing direction.
For more information please contact:
NovAtel, Inc.
1120 68th Avenue N.E.
Calgary, Alberta
Canada, T2E 8S5
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Phone: (403) 295-4500 or toll free in Canada and the U.S. only 1-800-NovAtel (1-800-668-2835)
Fax: (403) 295-4501