AutoCAD tips: Views, the UCS, and rotating the drawing

One of the most useful and confusing features of autocad is the UCS, the user co-ordinate system. Many people confuse the views and UCS’s, so I’ll try to clarify here.

The difference can make a huge impact on your work. The last thing you ever want to do is to rotate your model in model space so that north is up. This actually changes the model, and if others have referenced your work into theirs, rotating the model can cause serious problems with project co-ordination. Often you’ll have a model drawn in real world co-ordinates where true north is up, and then a UCS set for Project North to make drafting easier.

First, understand World UCS. Model space represents the world, in real units with north straight up. This is World UCS, or real-world co-ordinates.

Then there are any number of User-defined UCS co-ordinate systems. These are what allow you to make project north striaght up, even if your site sits with compass pointing 17 degrees East of North.

When you change to another UCS your crosshairs rotate, but the model does not rotate in model space. This is analagous to turning your set square to a new angle while leaving the drawing taped in the same place on your drafting table. You aren’t rotating the model, just rotating your drafting tools. This way you can draft lines parallel to the new UCS without having rotated the model. This is really handy when you want to draw lines or dimensions parallel to a wall or property line, especially if using the Ortho setting. Your dimensions will also display their text relative to the UCS that is active when a dimension is created.

The view controls whether or not your crosshairs sit parallel to the screen, but has no impact on drafting. View is analagous to turning your head when looking at your drafting table. It just makes it easier for you to read and draw, but has no bearing on the relationship between the UCS (your set-square) and the model (your drawing).

If the UCSFOLLOW command is on (=1) then the view will automatically change when you change to a different UCS. It also regenerates your drawing, so can slow you down in larger files. If UCSFOLLOW = 0, then when you change to a different UCS your view of the model won’t rotate, only your crosshairs will change to the new UCS orientation.