Construction Lines and layer organisation

I want to understand construction lines. Have started working with layer
naming quite recently.  Should they typically be placed on the dimension
layer, or is it better to create a separate construction layer? How does
LibreCAD identify or determine whether a line is a construction line?

Although I read about the construction view-hide icon # on each layer.
Thusly I do not knew how things work and what LibreCAD acts upon
when enabling construction line view on some specific layer.

https://docs.librecad.org/en/2.2.0_a/ref/fundamentals.html#construction-layers
https://docs.librecad.org/en/2.2.0_a/guides/dwg-setup.html#layers

Do a tutorial: https://dokuwiki.librecad.org/doku.php/tutorial:carport

Thank you for the reading references.  But construction lines are only described.
Could not find a tutorial about how one makes a line to be a construction line.
 
 

Heime wrote

Although I read about the construction view-hide icon # on each layer.
Thusly I do not knew how things work and what LibreCAD acts upon
when enabling construction line view on some specific layer.

Maybe I'm misunderstanding you. Any layer can be toggled into a construction layer to use on a temporary basis.

LibreCAD uses the layer setting, if Construction layer is set then it is a Construction layer, similar to show/hide or lock/unlock settings.

A construction layer is just a guide, it is not printed. Typically I'd use layer 0 but you can use as many as you want.

flywire wrote

Do a tutorial: https://dokuwiki.librecad.org/doku.php/tutorial:carport

A few tutorials would give you enough experience to solve most of your issues: https://dokuwiki.librecad.org/doku.php/tutorial:carport#construction_lines

There is nothing special about construction lines, each entity can be used to construct other entities by giving distance, intersection or other snap points.

The Construction Layer feature can be used on every layer, e.g. to find intersection points. Keeping construction layer visible can make a drawing unusable very fast. So toggle construction layer icon in the Layer list or make it visible only if it's needed.

It is good practice to put construction lines on a separate layer anyway. They are probably not part of the final drawing and need to be invisible for printing or checking the drawing.

So construction line is no property you can apply to an entity, just per your definition. It can be any entity you need to construct other entities.
Just like drawing on paper where you draw faint lines, circles or arcs to draw other entities.
There is already much geometry included in LibreCAD tools which make construction lines needless, but there are still many cases where it makes sense to draw a line, circle or arc for construction purposes only.

The interest is purely practical rather than descriptive.  

For instance

1.  How does one put construction lines on a separate layer?  
2.  How can one draw a line, circle or arc for construction purposes only?  How is it done?  
3.  Is it possible to have a line, rectangle, circle  or arc which is not a construction line?
4.  How can one make a set of lines that are construction lines and others that aren't?
5.  Let a line be shown as a construction line, how can that construction line be eliminated completely?

well, the easiest way -
1) create separate utility layer.  
2) activate it.
3) Put all lines that need to be constructional there - just draw them in utiliy layer. Mostly, just coner lines have to be constructional.
4) Mark that layer as construction.
5) switch to normal layer you use for your drawing.
6) Use contruction line for snapping etc.  while doing normal drawing.
7) Hide that utility or even remove it as it not needed. Also you may make it not constructional.

Notes
1) So far it's not possible to mix constructional (infinite) line and "normal" line in the same layer in LC (while Ray entity is supported by DXF format). I.e - within the same layer, either all of them are constructional, or all of them are not.
2) to put line on separate layer - either draw it initially on that layer, or move to another layer using Attributes or Properties commands.

Actually, constructional line is like normal line. It comes via start point and end point, but it has infinite length.

1.  Mark that layer as construction!  How?
2.  Remove a layer as  construction!  How?

When I make a line in a layer, and press #, its endpoints are extended automatically.
How can I stop that?  Currently, I have no control upon which lines get extended in
that layer.

Using Modify Layer Attributes and ticking Construction Layer is equivalent to
clicking on #.  Is it possible to have whether one clicks # or not, no lines gets
extended - meaning that a layer is purely non-construction.  A Construction Layer seems
to involve only a single flag designator with no control on the user on which lines get extended.

yes, right, you can't control whether individual lines are constructional or not. This is supported only on layer-level. So either layer with all lines is contructional, or not.

That' why I suggested you to create separate layer and make it constructional - while do drawing in another layer.

You may control layer attributes by click on layer's item in Layer View or Layer Tree widgets.

So it is LibreCAD that decides what lines gets extended or not when activating #
on some layer?  

The lines of a rectangle (as well as circles and ellipses) do not get extended. Only simple
2 endpoint lines get extended.  Does that mean that although a construction layer can have
multiple drawing elements, only lines with 2 endpoints get extended when pressing #.

It is strange that when making a construction layer, pressing the construction flag #
affect some lines, but leave others intact.  A construction layer is a layer where all elements
are constructions, no matter whether # affects individual elements or not.

Heime wrote

So it is LibreCAD that decides what lines gets extended or not when activating #
on some layer?  

Yes. And only straight lines are extended.

Heime wrote

The lines of a rectangle (as well as circles and ellipses) do not get extended. Only simple
2 endpoint lines get extended.  Does that mean that although a construction layer can have
multiple drawing elements, only lines with 2 endpoints get extended when pressing #.

Yes.

P.S Btw - how you may imagine extending circles? Ellipses? Polylines? What it might be?

Heime wrote

It is strange that when making a construction layer, pressing the construction flag #
affect some lines, but leave others intact.  A construction layer is a layer where all elements
are constructions, no matter whether # affects individual elements or not.

Well, that not a strange - it's just a convenient shortcut. Otherwise, the user should manage each contruction line individually, that is also not too convenient.

Plus again - which elements might be constructional except lines and how?

What I found misleading was the Construction Layer checkbox in the Layer Settings.

I made a new layer from the Layer List and set all elements in that layer as construction.
However, the Construction Layer checkbox seemed to imply that activating it would define
the entire layer as a construction layer.  Instead, what it actually does is only extend the
endpoints of lines infinitely.  Typically, I include many other construction elements in my
construction layer, not just those that LibreCAD extends through its checkbox definition of
Construction Layer.

The construction layer feature in LibreCAD mainly controls infinite extension of lines but as a user,
I often expect a broader definition of construction geometry on such layers.  It can easily cause
confusion regarding how this feature actually works.

What do you expect construction lines are? What is the definition? What should be their properties, how should they behave? Do you have experience in an other CAD system that provides construction lines the way you expect? Maybe the dxf format doesn't support this.
If you mean by construction lines auxiliary lines which do not appear on the print out, this can simply be achieved by setting the layer as not to be printed in the Layer List (greyed out printer symbol).
But you can not assign this to individual lines within a layer, as you can do with colour, width and line type.

By construction lines, I mean exactly what you described - any form of auxiliary entities
that do not appear in the final printout.  It seems I am using a broader definition than is
customary.

I am comfortable defining a layer using this broader definition, and it works well.  However,
the terminology could be clearer - terms like Infinite Line Mode (or similar) would better
express the actual action than the somewhat misleading term Construction Layer.  

In the case of an entire layer designated for any construction entity, whether the # symbol
is activated or not does not change the fact that the entities visible on that layer are still
considered construction elements.