topic Re: Linework shifts when Z value changed in AutoCAD Forum

Linework shifts when Z value changed

dmooreHP7RF — Thu, 21 Apr 2022 15:23:44 GMT

Some linework I have is acting very unusual, it is like it has its own UCS separate from the drawings UCS. If I draw a new polyline I can change the elevation freely, like normal. If I change the elevation on the existing linework, it shifts. It is acting like the linework is on a rotated UCS and even shows that when I try to edit a polyline(see attached).

Any ideas? This is new to me in my 20 years of doing this.

Re: Linework shifts when Z value changed

Kent1Cooper — Thu, 21 Apr 2022 16:03:12 GMT

It's not quite clear to me what you image is illustrating, but it looks like you are not quite in PLAN view, which would explain things seeming to shift when changed in elevation.

Re: Linework shifts when Z value changed

dmooreHP7RF — Thu, 21 Apr 2022 16:17:18 GMT

Hi Kent, thank you for the reply.

Everything is as should be, the rotated UCS you are seeing only appears when I do a polyline edit, in the image I attached I am editing the polyline that in this example is parking space striping. That UCS is a clue to what is occurring. If I change the Z value in the properties box from say....0 to -10000, it will move to the left along that slightly rotated Z axis.

Sorry if I am still unclear.

Dave

Re: Linework shifts when Z value changed

Kent1Cooper — Thu, 21 Apr 2022 16:47:10 GMT

@dmooreHP7RF wrote:

.... It is acting like the linework is on a rotated UCS and even shows that when I try to edit a polyline....

Then it is [on a rotated UCS, that is]. For further evidence, put this in at the command line:

(entget (car (entsel)))

and comply with the resulting Select object: prompt by selecting the Polyline in question. If the very end of the list that results is not

.... (210 0.0 0.0 1.0))

but the 210 is followed by different numbers, it confirms that the Polyline does not lie in [or parallel to] the WCS. The (210) entry in entity data is the extrusion direction, or the unit-vector "normal" or "up" direction for the object, with the numbers following the 210 being WCS XYZ coordinates of a point relative to 0,0,0.

You can also do:

(getpropertyvalue (car (entsel)) "Normal")

and select it, which will give you that alone [instead of the whole entity data list], which will be:

(0.0 0.0 1.0)

if it lies in the WCS.

Re: Linework shifts when Z value changed

dmooreHP7RF — Thu, 21 Apr 2022 16:52:33 GMT

Yes you were correct

(210 0.0545243 -0.0536981 0.997068))

Is redrawing the linework the only solution to fix this?

Thanks Kent

Re: Linework shifts when Z value changed

Kent1Cooper — Thu, 21 Apr 2022 18:05:42 GMT

@dmooreHP7RF wrote:

.... Is redrawing the linework the only solution to fix this? ....

You could use FLATTEN, but if the Polyline was accurately drawn within its own plane, some distortion would be introduced. If that's the case, I suggest:

1) MOVE the Polyline so that some vertex is on Z=0 in the WCS;

2) Draw a vertical LINE from some other vertex to Z=0 at the same location [use the .XY point filter];

3) Set a new UCS based on the Polyline, and then another with the vertex that's at WCS Z=0 as the origin, and the one you drew the Line from on the X axis, and go into PLAN view in that UCS. You should be looking at the Polyline edge-on, with the WCS-vertical Line showing the amount of tilt.

4) ROTATE the Polyline about the current UCS 0,0, using the Reference option to swing from the vertex-end of the Line to its other end. That will bring that vertex to the WCS XY plane without distorting the shape of the Polyline, but it could still be tilted in another direction, so:

5) Repeat the procedure using different vertices to bring the whole thing into the WCS XY plane.

Re: Linework shifts when Z value changed

TomBeauford — Thu, 21 Apr 2022 19:51:22 GMT

What template was the drawing created from?

With a projected coordinate system like we use in Map 3D a large change in elevation will appear to shift an object as you've describe.