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Why Use Contr Why Use Control P ol Points? oints?
Use measured control points to undistort the mapping artifacts when an especially high map
accuracy is needed, or if not enough loop closures are possible. Users will be able to gauge the
maximum remaining errors within a dataset. Control points will also allow for the automatic
alignment of datasets during post-processing. They will improve the accuracy of point clouds.
Why Does Drift Error Occur?
NavVis Mapping technology is based on SLAM algorithms that use the information from the
sensors to
incrementally build a 3D model of a building. This is a powerful and flexible approach,
but like many mapping technologies, it works by chaining measurement after measurement.
This chain of measurements is called the
trajectory estimate. You can think of it as a trail of
points describing where the device was,
relative to the dataset origin, and at which point in time.
Even though each individual measurement has very high accuracy, chaining many of them
together means that, over time, there can be a
drift error in the device's position estimate. This
can show up as distortions in the mapping results, such as a slight bending of long corridors
compared to the true building geometry.
How To Reduce Drift
Loop closures are one way to reduce drift. Our algorithms recognize previously visited places
and use that knowledge to adjust the trajectory estimate. However, loop closures may not be
feasible in every building layout, or you may need to achieve a higher accuracy to a higher degree
of certainty. This is where
measured control points come in.
Measured Control Points
Shown here is an example of how measured control points help you create a accurate map.
This graphic represents a building:
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