jubxie,
As with 2-D we can use the same tools for 3-D. Go to the Modify tool bar and use the add vertice command, but be sure your plane is rotated to the surface and you will not lose your Z value.
Regards,
Namdac

namdac,
Thanks for the response. My application is making maps using stereo imagery from arial photographs. We use only linestrings and cells to describe features in a top view. The 3d aspects are for topographic(contour)reasons only.We acheive the end 3d map using a "puck" or large mouse while looking at imagery/line work in 3d and "tracing" the ground.  My main problem is our contour's tend to collapse if there not enough verticies to calculate with. I can add verticies using the puck(this is a little clumbsy) or force the contours to not smooth/round off(makes contours ugly) In a perfect world id be able to, in a top view, just add a vertex to a line without affecting its elevation. This line maybe at 20.5' in z at one end an 57.4' in z at the other. I'm not sure how add a vertex at anything other then my existing "az". I appologize if im just not understanding how to apply your your previous response. Thanks

jubxie,
What you are describing is Photogrammetry? Correct? As with all tools in microstation the 3-D and 2-D tools do work in either with some exceptions,those I could write about for hours. On the main tool pallet use the Modify tool bar.
Regards,
Namdac

Namdac,

Thanks again. Photogrammety is correct. Pardon the elementary description. I will continue to work this out.

jubxie