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This tool does a sphere fit to find sphere in 3D data sets - eg Point Cloud -
Scorpion 3D Image
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Setup3D
coordinate system
- Reference - select a 3D reference for position
and results
ROI
Fit algorithm
- Fit only - run (possibly multipass - see Advanced) the
fit algorithm given by Method
- RANSAC only - run a single RANSAC fit only
- RANSAC + fit - run a single RANSAC fit, followed by (possibly
multipass - see Advanced) the fit algorithm given by Method
- Exhaustive - run RANSAC followed by a complete iterative fit
based on the algorithm given by Method
- Method -
- Nelder Mead - This algorithm is not based on a gradient or
other derivative of the error function. The method is based on having a simplex in
the search space for which the corners are evaluated. The simplex is
moved and transformed so as to continually shrink simultaneously with
the corner evaluations also decreasing, thus converging on what is hoped
to be a (global) minimum. How this transformation of the simplex is done
is not without freedom, there are some parameters to tweak, giving
variations of the method. With parameters as close to the original work
by Nelder and Mead as we have been able to figure out, we have made a
Classic Nelder-Mead , and with some more recent choices of parameters we
have found published on the internet, we made Variation I.
- Classic (30) - see above
- Variation (31) - see above
- Radius - initial guess
- Tolerance - max deviation from initial guess
- Decimations - max number of iterations (for Exhaustive
search)
- RANSAC count - max RANSAC iterations
- Min dist - minimum distance between points considered for a
RANSAC search
Advanced
Passes
The sphere fit can run a multipass fit procedure. The first option is
used to turn this on or off. (This is not available for the
Exhaustive search.)
- Multipass fit - selects single or multiple passes
- Max iteration count - never exceed this number of passes
- Stop if RMS improvement less than - do not process further if
RMS does not improve more than the threshold
- Stop if RMS less than - do not process further if RMS has
reached the threshold
- Stop if active point count below - do not process further if
less than the specified number of points remain
- Stop if active point percentage below - do not process
further if less than the specified percentage of points within the ROI
remain
- Stop if RMS deteriorates - do not process further, and ignore
last pass, if RMS increases
Constraints
- Point accept distance - used to filter outliers in multipass
fit and for the result (this is not used by the Exhaustive
search)
- Max fit RMS for accept - RMS filter to accept/decline the
result
- Minimum points for accept - point count filter to
accept/decline the result
- Minimum percentage for accept - point percentage filter
(within ROI) to accept/decline the result
Point cloud decimation (x & y)
- Factor - keep only every nth sample in x and y
directions
Point cloud filter
- Contrast - element 4 in a 5-element point cloud; set min and
max allowable value
Visualisation
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Sphere |
Found sphere |
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FittedPoints |
Accepted points within the ROI |
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InitialGuess |
Initial cylinder guess |
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Points |
All points within the ROI |
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ROI |
The ROI cube/cylinder segment/sphere |
Results
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Sphere center.x |
The found sphere center |
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Sphere center.y |
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Sphere center.z |
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Sphere radius |
Radius of found sphere |
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RMS |
Quality of fit |
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Loop count |
Total number of loops |
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Point count |
Total number of points within ROI |
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Fit count |
Used points |
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Fit percent |
Percentage of points used |
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