UCS Rotation from WCS?

[mdhutchinson]

How can I find the angle rotation between a UCS and WCS?

[dbroad]

How generalized do you want the answer?  It can get relatively complex.

For a simple case where the current ucs has only  a rotation is about the z-axis, this would work:

(angle (trans '(0 0 0) 1 0) (trans '(1 0 0) 1 0))

It would return the rotation of the z axis in radians.

If multiple rotations around various axes are present, it gets complicated.

[mdhutchinson]

I have an issue with 3rd party objects that refuse to stretch... I think it might have something to do with what may actually be a bug in AutoCAD (not the 3rd party software)

Think through the following - then try it.

1. Set LUNITES = 1    (Scientific Notation)
2. Set LUPREC = 8  (Max precision)
3. Set up a UCS that is 7.5 degrees rotated from the WCS.
4. Set Orthomode = 1  (O
5. Draw a few separate lines from an arbitrary point at a direct distance of 300 units.
6. Do a LIST command on the lines.
7. The Delta Y values should all be 0.00000000E+00 ... right?

(See the attached)

[dbroad]

No, they won't necessarily be the same.  There is a roundoff involved.  Limit of accuracy is 14 significant figures. When testing for equality, you need to add a fuzz factor. -1.4...E-14 is for all intents and purposes equal to 0.