Clients teach me new things nearly every day. This week the lesson I learned is the difference between using DVIEW to rotate your design on screen and rotating the UCS about the Z axis. All of my CAD career, I've used DVIEW. For a long time, when someone mentioned rotating the UCS in a 2-D drawing I would cover my ears and go "Llalalalalalalala." Before this week, all I knew is that rotating the UCS caused major problems in survey software.
The company I trained this week had always used the UCS to angle designs into a more comfortable drafting mode. After telling them that they should use DVIEW instead, they naturally asked, "Why?" At a loss for a real reason, I've taken it upon myself to dig deep and understand what the difference is.
A little background…
UCS stands for User Coordinate System. When you first enter a drawing your UCS lines up with the WCS. WCS stands for World coordinate system where Y is up, X is right and Z pops out of the screen at you. WCS is a nice, normal place, where things don't go wrong. In any new drawing, the world coordinate system lines up with the user coordinate system, much like a rectangular piece of paper whose edges line up with the edges of the desk it is sitting on. Rotate the piece of paper and you are rotating the Coordinate system. If instead you just started working on the drawing by scooting your chair to another position, that is more like what DVIEW > Twist does.
DVIEW > TWIST & SNAPANG
DVIEW is accessed by typing DVIEW at the command line. (Shocking, I know.) DVIEW stands for dynamic view, and represents the position of your eye (or in Autocad terms, the Camera) in relation to the canvas. After you start the DVIEW command, you are prompted to select objects or select a DVIEWBLOCK. I usually go for DVIEWBLOCK unless I'm just going to eyeball the rotation with a line or two as reference for the rotation. Type TW for twist and key-in your rotation angle. A positive angle will rotate the camera counter-clockwise.
You can leave the drawing as is, but your cursor will have rotated too. I usually use SNAPANG to untwist the cursor back to parallel with the bottom of the screen.
Rotate Coordinate System
To rotate a coordinate system, use the view tab and find the Z axis rotation. Enter the angle you wish to rotate the view.
Rotating the UCS is redefining where the zero angle is, therefore a positive angle will rotate the coordinate system clockwise.
Like DVIEW, the rotated UCS leaves you with a wonky cursor. Key-in PLAN, then hit enter for Current to straighten things up.
To un-twist from DVIEW, I type in PLAN, then W for world. (If you know of a slicker way, drop me a comment). To untwist a UCS, click the world button on the View tab.
Now that I understand the differences, I totally understand rotating the UCS if lots of text is going to get placed relative to the rotation. However, that is the only compelling reason to do it. Overall, I still recommend DVIEW over rotating the UCS. A drawing can only have one UCS at a time, but you can use DVIEW in every viewport if you wanted to. A rotated UCS can seriously impact how XREFS line up and how blocks are inserted. A rotated UCS will cause XREFs and blocks to come in at unexpected locations - you are changing the coordinate system after all!
Different dview twists can be set in different viewports
Text placement follows UCS
Works better when XREFS and blocks are inserted
Can use cad objects directly to set angle (DVIEW requires you to measure first)
Can be used in multiple viewports
Preferred method for many 3rd party apps
So next time one of your co-workers insists on rotating the UCS, you don't need to cover your ears and spout nonsense words. Get the whole story - then decide!
PS: Sign up NOW for my AU class Civil 3D for Beginners. November 29, 2011 1:00PM. Only a few spaces left! (Also, I bring candy.)