topic In trim command, why does polyline command L-shaped get trim while line command L-shaped not get trim? in AutoCAD Forum

In trim command, why does polyline command L-shaped get trim while line command L-shaped not get trim?

Anonymous — Tue, 04 May 2021 11:32:20 GMT

See the GIF attachment.

1. When I draw L-shaped using polyline command

→ it get trimmed

2. When I draw L- shaped using line command

→ it doesn't get trimmed

As I know tream works only when two line intersect each other

But

From point 1, I see even having no intersecting point in L shaped still it get trimmed.

So what is the geometrical logic behind it??

Re: In trim command, why does polyline command L-shaped get trim while line command L-shaped not get trim?

imadHabash — Tue, 04 May 2021 12:07:29 GMT

Hi,

>> As I know trim works only when two line intersect each other

In case of polylines you have a cut edge for the other attached polyline but NOT in case of line ( L shape ) . In general objects you select as cutting edges or boundary edges are not required to intersect the object being trimmed. You can trim or extend an object to a projected edge or to an extrapolated intersection; that is, where the objects would intersect if they were extended.

Re: In trim command, why does polyline command L-shaped get trim while line command L-shaped not get trim?

Kent1Cooper — Tue, 04 May 2021 12:13:40 GMT

@Anonymous wrote:

....

1. When I draw L-shaped using polyline command

→ it get trimmed

.... I see even having no intersecting point in L shaped still it get trimmed. ....

When a Polyline is selected as a Trim boundary, if it has more than one segment, its own vertices are "intersecting points" to trim to. Any segment picked on will be removed [to its end vertices, or less than that if it is intersected by something else closer to the pick point].

If you draw a Polyline of only one segment, you will find it is not removed under the situation in your image.

If you select the Trim boundary object(s) specifically, rather than hitting Enter for the <select all> option, you will have more control, and a Polyline segment such as in your example will not be Trimmed away if the Polyline itself is not a selected Trim boundary.

Re: In trim command, why does polyline command L-shaped get trim while line command L-shaped not get trim?

dbroad — Tue, 04 May 2021 12:37:24 GMT

It should be pretty obvious. Trim can't be used to erase the entire object.

Re: In trim command, why does polyline command L-shaped get trim while line command L-shaped not get trim?

Anonymous — Wed, 05 May 2021 07:33:29 GMT

When a Polyline is selected as a Trim boundary, if it has more than one segment, its own vertices are "intersecting points" to trim to.

→ But L-shaped have not intersecting point instead it has meeting point.

intersecting points : When two or more lines cross each other in a plane, they are called intersecting lines. The intersecting lines share a common point.

You know in L-shaped no two lines cross each other so the correct word is " meeting point" instead of "intersecting point"

Re: In trim command, why does polyline command L-shaped get trim while line command L-shaped not get trim?

Kent1Cooper — Wed, 05 May 2021 12:02:45 GMT

@Anonymous wrote:

When a Polyline is selected as a Trim boundary, if it has more than one segment, its own vertices are "intersecting points" to trim to.

→ But L-shaped have not intersecting point instead it has meeting point.

intersecting points : When two or more lines cross each other in a plane, they are called intersecting lines. The intersecting lines share a common point.

You know in L-shaped no two lines cross each other so the correct word is " meeting point" instead of "intersecting point"

Note that the red part above is still satisfied if the common point is at the end of either or both -- they do not need to cross each other and extend on both sides of the intersection. Any condition that will be "seen" by INTersection Object Snap mode qualifies, and that includes change-in-direction vertex locations on Polylines. That may not be your definition of "intersecting," but it is AutoCAD's definition.

EDIT:

However, I do find a peculiar behavior when there is a vertex without a change in direction. This Polyline has a vertex part-way along the longest stretch of it:

INTersection Osnap does not "see" that vertex. And if I choose the Polyline as the Trim boundary in a TRIM command, if I select that long edge on one side of its part-way vertex, I get a very different kind of result than if I select it on the other side:

vs.