Can't align UCS corretly to an object

[Karol-Or]

I want to align one of the axes to the line.

The origin now is on the line.

I use align UCS to object but it doesn't align the axes

[john.vellek]

HI @Karol-Or,

I rotate the UCS on the Z axis. Is this what you are looking to do?

Please select the Accept as Solution button if my post solves your issue or answers your question.

[Karol-Or]

I don't mean that line, the vertical long.

I attached a clean drawing

[paullimapa]

Try the UCS and 3Point option (as shown in attached png):

1st point is intersection

2nd point is endpoint of long line

3rd point is endpoint of the angle line

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[Kent1Cooper]

I believe what it's doing is using an endpoint of the Line as the new-UCS origin, but using the Line's extrusion direction  for the axis directions from there.  Since a Line is not "locked into" the XY plane of the current UCS when it's drawn, it can have a Z-direction difference between its ends, with its extrusion direction not perpendicular to its length.  It doesn't define a plane, but it still has an extrusion direction from when it was drawn.

Instead of using the OBject option in the UCS command, just pick two points on the Line [you can specify a third point or <accept> its assumption for the last prompt], and the X axis will be aligned with the Line's direction.

[Karol-Or]

I never understood the Extrusion Direction, how is it created?

[Kent1Cooper]

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@Karol-Or wrote:

I never understood the Extrusion Direction, how is it created?

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It's a unit vector representing the direction that the Z axis "aims" in World Coordinates for an object.  If you Extrude something with a positive extrusion distance, it's the direction that extrusion extends from the object; or, if you give something Thickness, it's the direction the thickness extends.  If you're drawing in the WCS, everything's extrusion direction when drawn is 0,0,1 [or, as expressed in entity data lists, (210 0.0 0.0 1.0) -- it's also the VLA "Normal" Property].  It will be different if something is drawn in a UCS whose XY plane is not parallel to the WCS XY plane, or if something has been Rotated 3D-wise from its original drawn position.

Some things [e.g. 3DPolylines] "have" one, from when they were drawn, that's kind of meaningless from the point of view of setting a UCS, since a 3DPolyline does not define one and can't be given Thickness [although you can Extrude one -- you get Surfaces rather than a 3D Solid].  Some things [e.g. non-planar Splines] don't have one at all.  Lines are peculiar because they can have delta-Z difference without  their extrusion direction being perpendicular to a plane they lie in, the way it must be for many object types [Circles, Arcs, 2D Polylines, Text].