QCAD.org Forum

I’ve run into a problem that I haven’t seen before. I’ve attached a DXF and created a YouTube video for illustration purposes.

In the attached DXF are two lines. The line on the right can be selected by dragging a rectangle to the left and downward (the rectangle has a blue/purple coloring). If this rectangle merely touches the line on the right - the line is selected. If I try the same on the left line I find that it cannot be selected using the same technique. Yet, the left line is selectable. Try it for yourself.

My question should be obvious. Why? Why is the line on the left behaving this way? Can the left line be altered to respond to selection in the same way that the right line can be selected? If so, then how?

FYI - the line on the left came from a step file exported from Solidworks, then opened in FreeCAD where the DXF was generated. I had to flatten the DXF in QCAD.

https://youtu.be/Ph8oGuQlL_Y

Definition: when I say “dragging a rectangle to the left and downward” I mean the following : holding down left mouse button while moving mouse cursor in the left direction and downward - causing a blue/purple rectangle to appear.

Hi,

A box selection L->R (bluish) selects all fully inside, R->L (greenish) selects all that that are fully inside and all that cross the selection box.
The color scheme seems to be switched somehow from what we were used to and I saw a commit with a fix for that:
https://github.com/qcad/qcad/commit/9b2 ... e52f60884f
The behavior must have been altered after v3.29.4.0 but I can not locate that.
Seemingly these defaults on missing, invalid or undefined preferences were always the opposite of what was intended


If you try the the second method merely crossing both entities then only the rightmost line entity is selected.
The reason is simple, the leftmost line entity is drawn on a plane where Z=0.035 units (Here mm but probably converted).

QCAD is basically 2D, most tools only work as intended in 2D.
But some resources handle distances or positions for example in 3D while others do that strictly in 2D.
Entities at Z=0.035 don't really intersect with a 2D rectangle at Z=zero.
But their endpoints are considered as fully inside the 'box' if that is the case in 2D.
In a way QCAD has no concept of an enclosed area, all is merely line-art.
Box selection L->R is then based on not intersecting but with all points inside or on the rectangle ...
... While box selection R->L are all the above and all that really intersect with the edges of the rectangle.

Apart from that, QCAD loads/renders/saves files containing 3D information just fine with a few but rare exceptions.
QCAD/CAM relies vastly on generated 3D information for example.
The general advice is to flatten your drawing to 2D before editing it with QCAD.
See: menu Misc .. Modify .. Flatten Drawing to 2D.
Remember that this modifies the drawing drastically without a way back in a later session.

This should have set all Z values of all coordinates to zero ...
It won't hurt in this case if you do that again.

To display Z coordinates in the Property Editor see:
menu Edit .. Application Preferences .. Widgets .. Property Editor
That may still report Z values rounded to zero depending the number of decimal places.
I have a script at hand that verifies for and/or selects things with Z not zero.

Regards,
CVH

CVH wrote: ↑

Sat Apr 20, 2024 5:14 am

The reason is simple, the leftmost line entity is drawn on a plane where Z=0.035 units (Here mm but probably converted).

Ah! I forgot to flatten the DXF. Thanks for your help!

CVH wrote: ↑

Sat Apr 20, 2024 5:14 am

To display Z coordinates in the Property Editor see:
menu Edit .. Application Preferences .. Widgets .. Property Editor

My Property Editor doesn't show the Z axis - just X and Y

Okay, I see what I need to do to display the z-coordinates. I need to check the "display z-coordinates" box. Now I can see the z=0.035 value for left line. Thanks for your help!

HappyShat,

What QCAD version are you running?
(See above forum rules in red)

From the looks of it, it is at least 3 years old.
A lot of things have been enhanced and/or fixed since then.
See QCAD Changelog:
https://www.ribbonsoft.com/en/documentation/changelog

Regards,
CVH

I'm on a Windows 11 Pro system using QCAD version 3.24.3.0 (build date is Mar 17, 2020)

Yeah, I should upgrade.