topic Re: mirror a UCS in AutoCAD Forum

mirror a UCS

Anonymous — Tue, 03 Nov 2015 13:54:49 GMT

Hi All,

I am trying to flip the UCS so that the X plane has a positive direction facing left (standard is right facing) and this will allow me to use the ID command to locate points in space. However I can rotate the UCS around the Z plane, but the ID command still produces figures just now with a negative value.

Does anyone know how to flip/mirror the UCS and have the values displayed in a positive?

Thanks,

Re: mirror a UCS

Kent1Cooper — Tue, 03 Nov 2015 14:02:46 GMT

UCS command, ZAxis option, accept default 0,0,0 as origin, give it 0,0,-1 as Z-axis positive direction. Or you can specify any point you want as the origin, and give it @0,0,-1 for the Z-axis direction.

Re: mirror a UCS

Anonymous — Tue, 03 Nov 2015 14:19:58 GMT

Hi,

I dont think I completly understand your answer. I dont want to flip the z-coords. I want to keep my proejct datum the same location but when I use the ID command I want the X value to report in a positve. (as if my north point was facing to the left of the screen. ACAD defults with the UCS northing to the right side)

Re: mirror a UCS

Patchy — Tue, 03 Nov 2015 14:33:44 GMT

USC, Y , 180 enter

maybe that's what you want.

Re: mirror a UCS

Kent1Cooper — Tue, 03 Nov 2015 15:59:50 GMT

@Patchy wrote:

USC, Y , 180 enter

maybe that's what you want.

That has the same effect as my suggestion, leaving the Z direction positive downward....

If what's wanted is to have X positive leftward, but still have Y positive upward on the page [or upward on the screen] and Z positive upward off the page [coming up out of the screen], I don't think that's possible. The UCS "follows the traditional right hand rule" -- see Help, "About the User Coordinate System (UCS)" [here for AutoCAD 2016].

Presumably you could get the effect you want by making a routine that would use ID but behind the scenes would reverse the sign of the X coordinate of whatever you give it. It could even undefine the ID command and make a different definition of it. Would something like that help?

EDIT: For instance:

(command "_.undefine" "ID")
(defun C:ID ()
  (command "_.id" (mapcar '* (getpoint "\nSpecify point: ") '(-1 1 1)))
); defun

If you're in the WCS, that reports locations you pick to the left of the Y axis as positive X values, and to the right as negative, and Y and Z values unaffected. If you type in coordinates, it takes tham in WCS terms and reports them back at you with the sign on the X coordinate reversed. If you have Blips turned on, it puts two in the drawing, at both the "real" and "adjusted" X-value locations, whether you pick a location or type one in -- I'm not sure whether that can be overcome.

It only affects the ID command -- it will not [for instance] give you a start of a Line at -1,0,0 if you type in 1,0,0.

Re: mirror a UCS

Anonymous — Wed, 04 Nov 2015 10:40:48 GMT

Hi Kent,

That is exactly the question I was asking. I should have made it a bit more clear as you have done. Its unfortunate that there is no easy solution to this issue. Its never arisen before but my client has their UCS aligned to pointing left-hand and it makes it easier to ensure tie-in points are the same. I can however do this manually.

Thanks for your assitance.