scurve trajectory planner

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1 year 7 months ago #324271 by Grotius
Replied by Grotius on topic linuxcnc scurve motion planner
Hi,

Here is the so called overfit. To show it better i made a cube.ngc test file.
  • The problem is clearly visible.
  • Its a full torsion turn of 2*M_PI over the clothoid fit.
  • It looks for the clothoid lib the solution is valid but unwanted for us.
overview:
 
closup cube corner:
 
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1 year 7 months ago - 1 year 7 months ago #324272 by Aciera
Replied by Aciera on topic linuxcnc scurve motion planner
Ah yes I have noticed those. Seems to me that it does not occur for fillets in the XY plane.
[edit]
which makes me think, are you still transforming the space corner to the XY plane to fit the clothoid as in the paper or are you skipping that step (as I believe you wanted to at some point). If you are fitting directly in 3d than that may have something to do with it.
Last edit: 1 year 7 months ago by Aciera.
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1 year 7 months ago #324274 by MennilTossFlykune
Replied by MennilTossFlykune on topic scurve trajectory planner


www.sciencedirect.com/science/article/pii/S0010448518304305
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1 year 7 months ago #324275 by meister
Replied by meister on topic scurve trajectory planner
WTF

the installer script from the first post have removed all user writable files on my system
[img

Code:
git clone https://codeberg.org/skynet/linuxcnc_scurve_compact cd linuxcnc_scurve_compact/cmake ./installer .... rm: cannot remove 'src/python3.11/Parser/Python.asdl': Permission denied rm: cannot remove 'src/python3.11/Grammar/python.gram': Permission denied rm: cannot remove 'src/kugel.scad': Permission denied rm: cannot remove 'src/MXM': Permission denied CMake Warning: Ignoring extra path from command line: ".." CMake Error: The source directory "/" does not appear to contain CMakeLists.txt. Specify --help for usage, or press the help button on the CMake GUI. make: *** No targets specified and no makefile found. Stop. make: *** No rule to make target 'install'. Stop. Current directory after build_cmake: /usr/src/MXM/linuxcnc_scurve_compact/cmake ./installer: line 9: cd: configs: No such file or directory ./installer: line 10: ./run_axis_9: No such file or directory Current directory after run_lcnc: /usr/src/MXM/linuxcnc_scurve_compact/cmake installer finished. odippel@odippel:/usr/src/MXM/linuxcnc_scurve_compact/cmake$ odippel@odippel:/usr/src/MXM/linuxcnc_scurve_compact/cmake/../.$ cd /usr/src/MXM/ odippel@odippel:/usr/src/MXM$ ls -l total 0
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1 year 7 months ago #324277 by meister
Replied by meister on topic scurve trajectory planner
my home directory is still there, puh, but

/usr/local/src/
/usr/src

and much much more other file are gone,
now i can re install my system and hope that nothing important is lost

WTF
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1 year 7 months ago #324280 by Grotius
Replied by Grotius on topic scurve trajectory planner
@Arciera,

The abstract proposes forward transformation (projection) to the xz plane.
Indeed the problem does not arise when there is no z value.
And yes we are directly fitting in 3d space.

The problem isn't there, when you do a plane fit. This is in fact a 2d fit solution in 3d space,
including forward & inverse transformation steps. We did this using the 2d clothoid lib in our
previous planners.

Maybe we can think about this problem and how to solve it using a 3d space fit.

You can state that this is a clothoid wich makes a full torsion turn, wich has no reason to do so.
  • I think the ceres is giving it a initial torsion value, and goes on with the torsion during fit iterations until a endpoint fit is found.
  • Why does it use this full torsion only in certain space corner directions? Is there a reason we don't know yet?
  •  
@Mennil,

The clothoid3d uses a non-linear solver to find the xyz endpos for the clothoid fit.
The solver will iterate to the desired endpoint in shortest way, naturally.

It's very unlikely for the ceres solver to give us a self intersecting result as shown in your picture,
unless we give incorrect input angles.

And it's unlikely we have infinite solutions regarding the 4-clothoid-spline fit.

 

The codebase ruled out self intersecting clohoids by making improvements to the abstract:  Abstract bug fixes
  1. In eq45, page 7, the Delta Theta is calculated by: Thetai4 - Thetai0.
    The clothoid Delta Theta produced by this substraction, is not alway's correct.
    When the incorrect value is used, it shows a self intersecting clothoid.     Eq.45 input Angles are in the range [0,-2pi], [0,2pi]. Substraction can lead to a incorrect
    Delta Theta.     To solve this issue, we convert back the thetai[x] into a xy vector.
    From here the signed angle between 2 vectors is calculated.

    This ensures a correct Delta Theta value.     Problably this is also the reason why in the abstract forward & inverse transformations are used.
    In this codebase forward & inverse transformations are obsolet
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