QCAD.org Forum

Please help me with what I should do, to create a closed polyline of the object with draw order 102, see the attached file.
I've exploded it repeatedly until it didn't explode any further, and then used the commands below:
Command: polylinefromselection (OC)
One polyline created
Command: polylinetoclosed (OE)
0 polylines logically closed
Command: polylinefromsegments (OG) - no effect

How do I change object wit draw order 102 into a closed polyline?
I need that to be an entity for a lasercutter to cut it out.

I'm running QCAD Pro version 3.32.5.0 (3.32.5) on W11.

Kind regards,
Arjan

Hi,

'Object with drawing order' can be ambiguous.
The drawing order is re-numbered on save/load counting from zero upwards.

'Object with handle' is more persistent and we can select that easily with: Misc .. Select .. By Handle (TH)

Detected 62 Polylines in Model_Space, 34 are logically closed.
28 are reported to be open but several are exploded text.

I suspect that at least the last 2 of this list must be closed:
- Duplicate slot of A5
- Duplicate slot of A7
- Something tiny in front of A12
- The problematic A11 (Drawing order 132 on open)
- The '2mm Balsa' shape

Duplicates can be selected by selecting (clicking) near them while holding down the ALT key.
Delete the shortest one, or the one that is not closed.

Also clean up the trailing segment in front of A12.

The '2mm Balsa' shape has an extra segment at the start (271.9997805, 171.712333) ... Use OD to remove that, then OE.

A12 has duplicate segments that trace back along the shape.
Probably also duplicate segments when exploded and QCAD merges anything that is connected at endpoints.

Use XP, MD, remove duplicates, OC ...
... OC will be logically closed if so ... What is a nice test that all selected formed a well closed contour.
... But re-tracing or back-tracing is not excluded.

OE can not close a polyline logical if it is geometrically open.
You could force a polyline to logically closed using the Property Editor ... This will include an extra segment from end to start.

Regards,
CVH

I'm working in modelspace, and qcad seems to behave differently in closing polylines of different objects (here: ribs for the tailfin of a modelglider).

First I'll react to CVH's observartions, then describe qcad's behaviour that puzzles me.
- Duplicate slot of A5 - the duplicate wasn't found by my qcad (MD), but I did find it manually, and removed the duplicate, and could than close the polyline, as wanted;
- Duplicate slot of A7 - the duplicate wasn't found by my qcad (MD), but I did find it manually, and remoced the duplicate, and could than close the polyline, as wanted;
- Something tiny in front of A12 - It wasn't identified when I used MZ. How did you detect that, what settings did you use with that tool?
- A11 is indeed the problematic entity (handle 0x1db1), in the enclosed file so alse are A9 (many handles, s it consists of many segments) and A13 (handle 0x2077).
- The '2mm Balsa' shape - that doesn't have to be closed, as it is a temporary marker for myself during editing and will be removed from the final file.

Colourcoding used:
red = to cut by laser
blue = to score/engrave by laser
white = entity to be edited into red or blue, or temporary marker during editing that will finally be removed
yellow = description in dutch of the problem (=cannot close polyline)

Now the puzzling behaviours of QCAD during my attempts to close the polylines/entities representing A9, A11, A13:
1. I cannot find duplicates using MD, nether through the command, nor through the icons in the menubar (Modify, Detection, Detect Dubplicates). That is the case with and without selecting entities. My settings are:
- Distance Tolerance: 0.001
- Angle Tolerance: 0.001
- Ignore layer & Ignore direction & Auto refresh are ticked
Question A: How do I succesfully detect duplicates with the MD-tool?

2. I could easily explode, adjust en close rib A15 (handle 0x2062), using XP, shortening the slot (trim-tools) and OC. However, the same order of tools doesn't lead to a closed polyline of rib A13.
Question B: What is the difference between the two ribs with regard to closing their polylines?
Question C: How can I detect that difference?

Hi,

Je kan me in het Nederlands een PM sturen als dat jou beter past.

Buntehuhn wrote: ↑

Tue Dec 23, 2025 9:03 am

the duplicate wasn't found by my qcad (MD)

No, MD only locates almost exact copies.
A partial re-trace is not an exact copy.
In your case that might if everything is explode to elementary lines and/or arcs.
Alt - select is the only way to detect partial overlapping shapes.
Select - delete - see what is left behind - undo is that also but undoing are new shapes.

Buntehuhn wrote: ↑

Tue Dec 23, 2025 9:03 am

Something tiny in front of A12 - It wasn't identified when I used MZ

MZ has a lower bound, see Options Toolbar.
The tiny thing was found with the Selection Filter (GF): Type .. 'Polyline' Property .. 'Closed' .. Not true.
Selected they display markers and those have a fixed size, pixel based.
Easy to locate where endpoints or vertices are, in any zoom state.


General approach closing A9 - A11 - A13:
- Double click near A9, hold down the Shift key and double click near A11 and near A13.
=> See Property Editor: Selection All(24) -> 2 Polylines, 11 lines, 11 Arcs
>> Avoid to select and explode circles ... Or clear that preference for XP.
- Explode the selection XP
=> See Property Editor: Selection All(63) -> 31 lines, 32 Arcs
- Detect duplicates MD (Default settings are fine or adapt options as they suite you)
=> None found ... Terminate MD, keep selection.
- Convert to polylines OC
>> 3 are created what already looks promising for 3 contours.
>> But none is closed ... Bummer.

Now select each generated polyline apart and look for the red starting marker.
The polyline is expected to be open at start vs end.
Zoom in on the area around that marker ... Aha

Bottom line: Iets zorgvuldiger tekenen.

Regards,
CVH

Excellent, I'll try myself with the filter options for PG.
Thanks for your offer to PM, English is fine for me and publicly progressing rather than PMing might benefit other users more

That worked: filtering for non-closed polylines in the PG-tool.
Found a view gaps/not connected segments, and closed those with OC.
FYI I've attached the resulting file.

Seems better ...

A few minor comments:
- A2 are loose entities.
- Circles in A1, A3 and A9 are polylines ... It all depends on what you prefer.
Some drivers can't handle full circles.
- There are 90 unused and empty blocks in the Block List.
BP will purge these.

Regards,
CVH

Thank you, fixed the circles as well. What command did you use to find the circles that weren't circles but polylines?

Buntehuhn wrote: ↑

Mon Dec 29, 2025 6:47 pm

What command did you use to find the circles that weren't circles but polylines?

There isn't really a method for that.
It is a Polyline shape that resembles a Circle.
And because it are Circles in the other profiles I took the time to mention the difference.

First have a look at the 'Explode' (XP) preferences under:
Menu Edit .. Application Preferences .. Modify .. Explode.

If you don't want to explode Circles in selection then un-check that.
But know that Circles are not supported for CNC based on G-Code.
Don't worry, QCAD/CAM will handle that.

Only if your CNC target is that old or doesn't support Arcs (G2/3) at all then explode Splines to Lines.
Otherwise opt out for the line explosion and choose the Spline tolerance wise.
The smaller the approximation tolerance, the more and smaller tangentially connected Arcs are generated to explode a Spline.

Don't overdo the number of Arc segments per full ellipse what can turn out problematic for small shapes.

Seemingly or intended connected Arcs pose a mathematical problem when too small and/or too short.
The source of issues are fixed internal tolerances and the limitations of the number system.
It is a lesser problem for Polylines with 'Arc-like' segments ... Bulging segments.
But again problematic in conversions from and into Polylines.
At some point, I must revert to microns instead of mm.
=> Real size and fixed tolerances are the same but the values are 1000 times larger.


There are in fact several types of (almost) circular shapes.
- A Circle, the most basic one.
- One fully circular Arc but that is a problematic shape on its own.
- 2 semi-circular Arcs with the same center and radius.
- A closed contour of 2 or more Arcs with the same center and radius summing to a sweep of 360°.
- A Polyline with one of the 3 above as segments.
- A full ellipse with a ratio near 1.
(Know that there is no analog to a Circle, a full ellipse is an analog of a full circular Arc with similar problems)
- A closed contour of Ellipse-segments with the same center and ratios near 1.

Where we use the term 'the same', it can also be almost the same.
Then it only looks circular but it isn't.

I once scripted a tool to convert exploded Circles back ... Don't look for it, scripting is not really backwards compatible.
Just redraw the Circle and trash the Polyline.

Last advise in this matter:
- Don't overdo explosion and re-combination of the same Polyline shapes, the conversion of arcs to bulging segments or back is not utterly certain.
- Trim every 2 loose shapes intended for segments pair-wise (TM) before creating a Polyline.

Regards,
CVH

Thank you again.
I fixed the circles and excluded them from XP.
I'll adopt the practice to combine segments rather than repeatedly explode and create polylines.

Leaves one remaining question, regarding alt-select to identify partly duplicates. Pressing the Alt-key while selecting entities doesn't do anything.
How should I correctly do 'alt-select' ?

Buntehuhn wrote: ↑

Wed Dec 31, 2025 12:50 pm

Pressing the Alt-key while selecting entities doesn't do anything.
How should I correctly do 'alt-select' ?

When there is nothing to 'Alt-select' between ...
... If there only one entity nearby ...
It select that nearby entity ...
... Otherwise it presents a list, in the mean time displaying a few properties.

Regards,
CVH