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useful when there is a lot of z error in the GNSS data but the x, y data is good. If you check this
box, you may want to lower the elevation threshold to .01 to give Stencil more flexibility in the
vertical domain.
Trajectory in Camera Coordinate System?
– You can have Stencil automatically determine the
correct selection or you can select the Laser or Camera coordinate system manually. Stencil uses
the offsets in the parameter file to correctly align the data from the GNSS and the Stencil 2
trajectory. In Mapping / Localization without the feature tracker the trajectory is relative to the
mid-point of the lidar. When Mapping / Localization with the feature tracker the trajectory is
relative to the mid-point of the front lens of the camera.
Super Tip:
Using GNSS data in the Loop Closure Tool can be problematic if there are a lot
of issues with the data. Here are several approaches to improve your results.
•
Edit the GNSS data directly to eliminate bad points. You can do this with a text
editor or in CloudCompare.
•
After running the loop closure tool once, there is a file of the GNSS data used for
Loop Closure. It might be easier to edit this loop_closed GPS file than the full file.
You do not have to have lots of GNSS points to accurately reduce/eliminate
global drift errors.
•
Filter the GNSS data file using your own methods to remove unwanted points.
•
Apply RTK post corrections to the GNSS data using the PPK process before
running loop closure for best results.
•
If you have an independent way of measuring elevation, you could substitute
that data in the GNSS file.
The fourth tab lists seldom used and more
advanced options. The current options
include parameters for correcting errors in
the Velodyne Sensor. These should be left as
zero unless you are trying to correct a scan
with drift or geometric scaling issues that do
not start and end at the same place.
Roll Correction Factor –
This is
included for
completeness. It is probably not very useful
for correcting point clouds.