2D in a 3D World

This post is going to address another one of the more common AutoCAD conundrums that people run into.  Most people are trained to use AutoCAD in 2D.  However, even when working in a drawing that is two dimensional, AutoCAD always has the potential to draw objects in 3D.  This becomes a problem as people model more in other software and then transfer those drawings to AutoCAD.  It is common for users to forget that the base drawing is actually a 3D model which means that when they snap, they are really creating linework at elevation.

One of the easiest ways to prevent drawing in 3D is to use the OSNAPZ variable.  An OSNAPZ value of 0 will snap to a 3D elevation.  A value of 1 will always draw at the value of the ELEVATION variable (which by default is set to zero).  This is the easiest way to prevent drawing at elevation in the first place.

Sometimes everything has already been drawn in and it’s too late to change the value of OSNAPZ to 1.  A 3D orbit (the 3DO command) will help verify if things are drawn in 3D.  If the drawing contains a mix of 2D and 3D elements, orbiting can be difficult due to the large distance between objects in the Z direction .  The PLAN command restores a 2D view after orbiting. In order to restore things to a nice level plane, we can use the FLATTEN command.  This is an Express tool, that will quickly convert objects to 2D.  It is recommended that you save your work before executing the command.  When it asks if you want to “Remove hidden lines?” use the default of No.  If you’ve got blocks in the drawing with 3d components, you may need to explode them first.

FLATTEN does not always work, and in the case that it does not, it may be necessary to remove the elevations by rounding them out with the following commands.

1. Select the objects.
2. Enter the Move command.
3. Use the Displacement option.
4. For the value, use 0,0,1E99 (the move command is now done).
5. Enter the Move command again with no objects selected.
6. Type P for previous and hit Enter twice.
7. Use the Displacement option again.
8. For the value, use 0,0,-1E99 (note that this drops everything back down 1×10⁹⁹ because of the negative).

Note that this will only work on objects in the current drawing.  If you need to modify objects in external references then you will need to open those drawings up and fix them too.