What constitutes an "entity"?

[DenisH]

I draw a rectangle. I try to select it, but seem to select only one or two sides of it. It seems these sides are "entities". Is it not possible to have a structure of lines be an entity, short of creating a block? I am accustomed to a 20+ year old 2D CAD system in which any set of selected parts can be grouped for easy moving around the drawing yet can be edited in place. Will the professional version help?

I am using the community version in Sonoma 14.6.1

Thanks,
-Denis

[CVH]

Hi, and welcome to the QCAD forum.

When drawing a shape from the Draw .. Shape category please consult the Options Toolbar.
Typically left above the drawing panel.
Activate 'Create Polyline' to draw it as a polyline with connected line segments.

Most QCAD tools share this Toolbar to list their options.

QCAD has no named (closed) shapes as we know them, e.g.: Square, Rectangle, Hexagon, Star, ... Except Circle and Ellipse.
All can be drawn as loose line segments or as a polyline.

For the rectangle shape from 2 points see: Rectangle (RE).

A comprehensive reference for almost all QCAD tools: QCAD online reference
Or see menu Help .. Reference Manual.

Regards,
CVH

[DenisH]

This is most helpful, esp. the options toolbar. I also have noted that double clicking on a part selects all connected parts.
Related to this, how is it possible to connect a line not at an end? I can snap to the middle of a line, but that does not appear to "connect", in the sense that a double click indicates they are not connected.

-Denis

[CVH]

The Options Toolbar is one of the most important things to keep an eye on.
For a novel user with QCAD also look at the mouse icon in the middle of the Status Bar.
The mouse button tooltips will guide you through the current active tool.


Double clicking on a drawing entity selects all connected line-art at endpoints.
Sometimes misinterpreted as selecting a closed contour.
Only true when the entities form a distinct closed contour.

There is an application Preference for the connecting tolerance.
See: Application Preferences .. Graphics View .. Behavior
For some other types of drawing entities, double clicking means something else.


Snap points are typically used while drawing new things, while modifying, not for selecting.
One would never be able to select vector art its endpoints or middle based on a pixel position in any zoom state.
When snapping is in order:
- For new entities, typically the snapping options are displayed at the left, typically Auto Snap is active.
- While modifying they are not but they are still available under the menu Snap, again typically Auto Snap is active.


A single left click near a drawing entity selects it.
An edge of a rectangle drawn as line segments is an individual and unrelated line segment.
Drawn as a polyline it selects whole the polyline, whole the drawing entity.
When selected you also see specific markers, little colored squares.

One can drag these markers to a new location. Click and hold on the marker, move a little while holding down the mouse button.
The marker will stick to your cursor and you can release the mouse button.
Dragging an endpoint of a line segments alters that endpoint position, the length of the line but that may also affect the orientation.
One can drag the whole entity by clicking an holding nearly on and near a marker, avoiding the marker itself.
After a little motion whole the line segment will stick to your cursor and you can reposition it.
This doesn't affect the length nor the the orientation, for line segments it affects both endpoints simultaneously.

While dragging, typically Auto Snap is active for the new location.


Perhaps have a look at the Video Tutorials

Regards,
CVH

[DenisH]

"There is an application Preference for the connecting tolerance."

I have been looking for this. I see a double click to select tolerance, but nothing which would connect two lines at the middle. It seems that polylines can only be connected at the ends. So a drawing in which a human would call two lines connected QCAD will not unless the connection is at an end. This characteristic is something I will have to get used to. I think it is why there is no tool to draw a line perpendicular to another line from a remote point. Even so, it could be done by breaking the single line into two connected collinear polylines

What does Auto snap do? Make a guess as to what I want?

I am trying to learn, but it is difficult.

-Denis

[CVH]

Hi,

So a drawing in which a human would call two lines connected QCAD will not unless the connection is at an end.

A Line segment that has one endpoint on another Line, or curve in general, is merely touching.
Mutual connected Line segments touch at endpoints.
Interconnected line-art touches at endpoints.
So no, 'touching' can not be considered as 'connected' in general.

It seems that polylines can only be connected at the ends.

A polyline is a string of segments connected at nodes or vertices.
Polyline segments can be straight or bulging out to the left or the right seen from start to end.
A vertex (geometry) is a point where two or more curves, lines, or edges meet.
From a Polyline perspective:
- Excluding 'more', excluding a Ray or an endless Line.
- Every vertex is associated with the bulging nature of the segment that starts at that point.

The similarity of a bulge or bulge factor equal to zero, not bulging or a straight segment, with a Line segment is straightforward.
That is not really true for segments with a bulge factor different from zero compared with Arc segments.
Arcs have a center, a radius and 2 end angles, bulging segments have 2 endpoints and a sweep angle = 4*atan(bulge).
The conversion of a bulging segment to an Arc or vice versa is never exactly 1:1.
An Arc can be fully circular, a bulging segment not: tan(360°/4)=tan(90°)=Error (Infinite).

One can convert connected Lines and/or Arc segments to a polyline with the Polyline tools.
One can decompose a Polyline to Line and/or Arc segments with Explode (XP)

With only straight segments, sometimes called a Polyline with Lines.
If it contains bulging segments, sometimes called a Polyline with Arcs or with Lines and Arcs.
But in fact: A polyline does not contain Arcs nor Lines shapes.

I think it is why there is no tool to draw a line perpendicular to another line from a remote point.

... There are several way to do that.
When the perpendicular point is on the line-art, a perpendicular snapping point exist.
This is not limited to lines or Line segments.
Typically Snap Auto (SA) is active, the hint at the snap point can be ambiguous.
A perpendicular point can coincide with another named snapping point.
In that case one can force to snap to perpendicular points only (Snap Perpendicular (SU)).
When it is not on the line-art then you can still force snapping to a perpendicular point.
Indicate near the target entity, the closest perpendicular point will be proposed.

The other way around would be an orthogonal Line (OL) and then extended or trimmed to the Line segment.

Even so, it could be done by breaking the single line into two connected collinear polylines

I don't understand why that should be collinear Polyline shapes, two collinear Line segments will do.
A polyline with one single straight segment is possible but not advisable.
The only advantage would be that Polyline segments have an middle marker when selected.

What does Auto snap do? Make a guess as to what I want?

Auto snapping or Snap Auto (SA) snaps to the nearest of all snapping points for the line-art near your cursor.
For a (configurable) list see: Application Preferences .. Snap .. Auto Snap.

As said, the hint at the snap point can be ambiguous.
For a new Line from a distinct point to a Line segment that can be:
- Any existent intersection with the Line segment.
- An endpoint.
- A middle point.
- A perpendicular point.
- A grid point if that is nearer to your cursor than the above.
- Any point on the Line segment.
In this order of appearance.
If the perpendicular point coincides with the middle point, then the snapping hint is 'Middle'.

Regards,
CVH

[DenisH]

Thanks, I think I understand the issues.
-Denis