As many users have undoubtedly noticed, there is no longer a Depth Lock option in V8i. While this may be alarming to those who used to rely on Depth Lock and Active Depth to draw accurately on a desired plane, keep in mind that the functionality of Depth lock still exists. However, the concept has changed. This article was written to help users switch from using Depth Lock to using the modern tools available in V8i.
Depth Lock and Active Depth were used together to set the plane at which elements are drawn in a 3D file. The Active Depth is always a plane perpendicular to the view window perspective. This means that if you rotate the view or fit view, etc., the Active Depth will change. Depth lock was used to lock your drawing to the Active Depth in your drawing. Even when snapping to an element at a different depth, the element you are drawing or placing will be put on the Active Depth. With Depth Lock turned off, elements will be drawn at the Active depth unless you snap to an element at a different depth.
V8i now uses Auxiliary Coordinate System (ACS) planes when working in your drawing. The short explanation of how to mimic Depth Lock is to turn on ACS Plane Lock and ACS Plane Snap Lock.
ACS has gained more features and is implemented in V8i differently than it was in previous versions of MicroStation. Previously, you could only have one ACS active at any one time. Now, you can have an ACS defined in each View window. The per-View ACS behaves exactly like the Active Depth setting in previous versions of MicroStation. It is dynamic, meaning that it can (and will be) reset by performing a Fit View, by rotating the View, or by changing the Active Depth.
However, there's also the static ACS. There are a few different ways to set the ACS but the end result is that the ACS determines your origin and the orientation of coordinates. So, you can set up an ACS that is aligned with the Global Origin of the file, or you can align it in any other way that you desire.
All of this is important to understanding what the ACS Plane Lock and ACS Plane Snap Lock actually do. The ACS Plane Lock will lock your new elements to the ACS plane, as long as you don't snap to an existing element. This is easiest to understand if you think of a simple line being placed in a separate area away from other elements. The ACS Plane Snap Lock goes one step further. Let's take a look at some illustrations to help explain the difference.
In the drawing below, I have a simple 3D environment with the standard Top, Isometric, Front, and Side views open. There is a solid block already in the drawing. I have defined an ACS plane that is aligned with the Global origin of the file. Here's what happens when ACS Plane Lock is turned on, and I draw a line "next to" the existing element in Top view:
Notice in the Front view that the line is even with the ACS triad (origin). It is also at a higher elevation that the solid. Here's what happens when I draw a line by snapping to the two end points of the solid:
As you can see, the line is no longer on the ACS Plane. It is aligned exactly with points that I snapped to. Let me draw the second line again. This time I will use a yellow line, and I will turn on ACS Plane Snap Lock:
Notice that even though I snapped to the solid, the yellow line remained on the ACS Plane. As you can see, this allows you make use of the same functionality as the old Depth Lock, while integrating with the enhanced ACS Plane system that has been implemented by V8i.