OCS Visual

[samifox]

Hi

 

the docs describe OCS like this

 

  Quote

To save space in the drawing database (and in the DXF file), the points associated with each entity are expressed in terms of the entity's own object coordinate system (OCS). With OCS, the only additional information needed to describe the entity's position in 3D space are the 3D vector describing the Z axis of the OCS and the elevation value.

For a given Z axis (or extrusion) direction, there are an infinite number of coordinate systems, defined by translating the origin in 3D space and by rotating the X and Y axes around the Z axis. However, for the same Z axis direction, there is only one OCS. It has the following properties:

Its origin coincides with the WCS origin.

The orientation of the X and Y axes within the XY plane is calculated in an arbitrary but consistent manner. AutoCAD performs this calculation using the arbitrary axis algorithm (see Arbitrary Axis Algorithm).

 

Once AutoCAD has established the OCS for a given entity, the OCS works as follows: The elevation value stored with an entity indicates how far to shift the XY plane along the Z axis (from the WCS origin) to make it coincide with the plane that contains the entity. How much of this is the user-defined elevation is unimportant.

Any 2D points entered through the UCS are transformed into the corresponding 2D points in the OCS, which is shifted and rotated with respect to the UCS.

 

 

i visulze that proccess like that :

 

User adopt new UCS and draw a circle, than the circle points were translated to OCS using the elevation and Z vectror.

 

 

am i right?

 

Thanks

Shay

[marko_ribar]

You permuted UCS with OCS... UCS is active plane in witch you draw entities (arrows in the center of circle may approximately correct correspond to UCS, but it may not be exact true; UCS is system witch is coplanar with drawn one in center of circle, so when in UCS you can draw circle in that plane - you can draw circle with circle command)... OCS on the other hand is system witch is parallel to drawn object in 3D space, but its origin doesn't match origin of corresponding object in 3D space - its origin is WCS 0,0,0 point... But remember OCS is parallel to drawn object in 3D space... So to me it looks that you almost post correct picture, only you presented OCS as UCS and UCS as OCS... Elevation data is presented correct - it's elevation measured from OCS (WCS 0,0,0 point) to center point of its corresponding object in 3D...

[samifox]

  marko_ribar said:

You permuted UCS with OCS... UCS is active plane in witch you draw entities (arrows in the center of circle may approximately correct correspond to UCS, but it may not be exact true; UCS is system witch is coplanar with drawn one in center of circle, so when in UCS you can draw circle in that plane - you can draw circle with circle command)... OCS on the other hand is system witch is parallel to drawn object in 3D space, but its origin doesn't match origin of corresponding object in 3D space - its origin is WCS 0,0,0 point... But remember OCS is parallel to drawn object in 3D space... So to me it looks that you almost post correct picture, only you presented OCS as UCS and UCS as OCS... Elevation data is presented correct - it's elevation measured from OCS (WCS 0,0,0 point) to center point of its corresponding object in 3D...

 

Hi Marko,

 

so...the UCS is the system above?

[marko_ribar]

Yes, you can draw in it as many objects as you wish with standard commands for drawing...

[samifox]

Thank you Marko!