You can create a series of section elements and create a surface form sections using more than two sections.
The direction of the elements must match - left to right or right to left, clockwise or counter-clockwise. If they close, the start points should also align.
I used display depths and rotated views - some via key-ins, some graphically. There is also a delta display depth key-in so you can easily move forward and backward in your slice. For example, if your view is aligned so the view Z runs from the front to the rear of the tank and you are looking at a specific depth slice, like 1' or 0.5 Meters, to "step forward or back 5 units at a time, the key-in DD=5,5 or DD=-5,-5, followed by a data point in the view, will move you forward and backward 5 units. It basically is moving both the front and rear clipping planes for you in unison.
Then, at each slice, you trace an outline. In a few minutes, you have a multitude of sections to make a surface from.
Other useful key-ins:
RV=90,0,0
RV=0,90,0
RV=0,0,90
Copy View
Rotate View Points
The 3 point view rotation must be done with with the Z axis locked so that the rotation is only around a single axis.
This is useful to align the view and model so that the 90 degree rotations above will allow you to quickly make a top, front and side view of a scanned area when the scan axis is not aligned with the target object.
Some of these can be used with Auxiliary coordinates, but the truth is, I have done many a model without using a single auxiliary coordinate system.
