QCAD Bugtracker

  • Status Assigned
  • Percent Complete
    0%
  • Task Type Bug Report
  • Category QCAD (main)
  • Assigned To
    Andrew
  • Operating System All
  • Severity Very Low
  • Priority Very Low
  • Reported Version 3.20.1
  • Due in Version Undecided
  • Due Date Undecided
  • Votes 1
    • CVH (31.05.2018)
  • Private
Attached to Project: QCAD Bugtracker
Opened by CVH - 29.05.2018
Last edited by Andrew - 04.06.2018

FS#1765 - Errors with polyline offset

Win 7 32 bit QCAD 3.20.1

Ofsset of a base-line with arcs results in massive ammount of errors.
Most of them occur as a cluster of very tiny segments and are part of the offset. (zoom far in at the red circles)
Mostly they occur where the offsetted arcs should merely be trimmend pairwise.
Some occur as detached entities or as detached strings of entities very near the offset (strings not documented).
Spooks occur at opposite site when base-line is not closed.
360° curls can occur with R = Offset.
Null-entities may occur (not documented, hard to find and not able to copy).

The base-line is checked and sound and has mixed tangentially or not tangentially connected arcs.
Offsetting the mother base-line of the base in the file has similar effect but not all and/or different ones.
Also encountered with offseting polys from fonts.
Used to define pocket paths for CNC.
Detected because the CNC driver will not accept Self-crossers, Null-entities or open ends depending on the settings.

Work arround is to explode and select small entities but this does not solves the issues.
1) Choosing the tolerance large enough will detect small segments that should stay.
2) Recombining will generate new ones at the place where the main segments remain crossed.
Cleaning up the paths is a daunting process with some thousand segments for several offsets.

I assume this has an infuence on the CAM part of QCAD too unless the offset method is different.

Admin
Andrew commented on 04.06.2018 14:54

These are known tolerance issues and can likely not be resolved. There is always a lower limit at which segments can no longer be recognised as such and the offset algorithm fails. The recommended solution is to clean up the paths, joining small segments into larger ones, etc.

CVH commented on 06.06.2018 05:53

The alternative function under Misc produces less errors - no ghosts and these are more easily dedected. They are >300° / ←300° arcs. Placing them on a temperary layer after exploding gives a guidline to where to trim overshooting segments.
Recombining with a small tolerance will end where small crossings remain.
When recombination reached the end of the string move the single polyline to yet another layer and kill all what is left.
Time saved is about 9 to 10.

Regards

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