NormalX,NormalY and NormalZ of property of the circle

[wimal]

When I get the property of a circle it display NormalX=0 NormalY = 0 NormalZ = 1.0

Please can you explane what is that. And after change the ucs it will change to some other values. After that all other circles (eaven newly drawn) get this value.

The problem is after changing the UCS I cant obtaind the correct value of the center coordinates by lisp.(CAD 2006)

[MSasu]

The problem is after changing the UCS I cant obtaind the correct value of the center coordinates by lisp.(CAD 2006)

Please keep in mind that the coordinates in associated lists are in WCS coordinates. To have them in current UCS please check TRANS function.

[Lee Mac]

Please keep in mind that the coordinates in associated lists are in WCS coordinates.

 

This is only true for non-planar entities (such as Lines, Points, 3D Polylines etc.) with some planar exceptions (Ellipse, MText), and extrusion vectors (DXF Group 210) which are always defined in WCS.

 

For most planar entities (Arc, Circle, LWPolyline, Insert, Text, Attrib etc.), the defining coordinates are expressed with respect to the OCS (Object Coordinate System) which is defined using the Arbitrary Axis Algorithm, given the normal (extrusion) vector for the entity (DXF Group 210).

[wimal]

Thanks gentlemen for explaining this.

[lrm]

The plane which a circle lies is defined by the normal ( a vector perpendicular to the plane) and the distance that plane is from the WCS origin. A plane with a normal of x= 0, y = 0 , z = 1 is parallel to the XY plane. DXF code 210 stores a circle's normal. DXF code 38 the elevation (the distance the plane is from the origin). If you were to rotate the circle by 45° about the Y axis, the 210 code would read (210 -0.707 0.0 0.707), a vector pointing at 45° in the XZ plane. It should be noted that the 3DROTATE command follows right-hand rule convention for the X, Y, and Z axes, but the ROTATE3D command has a bug and uses a left-hand rule for only the Y axis when rotating an object in 3D space.

[danellis]

That might explain why I can never get my 3d rotations right first time. I always try to use a left-hand-rule!!!

 

dJE

[marko_ribar]

The plane which a circle lies is defined by the normal ( a vector perpendicular to the plane) and the distance that plane is from the WCS origin. A plane with a normal of x= 0, y = 0 , z = 1 is parallel to the XY plane. DXF code 210 stores a circle's normal. DXF code 38 the elevation (the distance the plane is from the origin). If you were to rotate the circle by 45° about the Y axis, the 210 code would read (210 -0.707 0.0 0.707), a vector pointing at 45° in the XZ plane. It should be noted that the 3DROTATE command follows right-hand rule convention for the X, Y, and Z axes, but the ROTATE3D command has a bug and uses a left-hand rule for only the Y axis when rotating an object in 3D space.

 

The plane which a circle lies is defined by the normal ( a vector perpendicular to the plane) and the distance that plane is from the WCS origin defined by center point of circle. DXF code 38 the elevation (the distance the plane is from the origin), only if LWPOLYLINE is issued entity - if it's CIRCLE, as I said, center point position in space and DXF code 210 - normal vector of OCS plane, defines 3D space plane in witch lies circle...

 

As no one gave an example, here is used OCS of reference CIRCLE to extract OCS center coordinates into WCS center coordinates, using (trans) function and source OCS defined by DXF 210 and destination WCS - 0 integer for (trans) transformation point coordinates...

 

(defun c:circen ( / ss ci cen )
 (prompt "\nPick circle")
 (while (not ss)
   (setq ss (ssget "_+.:L:E:S" '((0 . "CIRCLE"))))
 )
 (setq ci (ssname ss 0))
 (setq cen (trans (cdr (assoc 10 (entget ci))) (cdr (assoc 210 (entget ci))) 0))
 (prompt "\nCenter of circle in WCS is : ") (princ cen)
 (princ)
)

 

M.R.