When you are creating 3D Lines, note the status of [F6] 3D Cursor. When this is enabled, DataCAD will expect three-dimensional coordinate input. The message line will say "3D cursor input. World coordinate snapping enabled."
If you toggle the [Insert] key while the 3D cursor is enabled, you'll find there are three input methods:
- Relative / Absolute Cartesian (X, Y, Z)
- Relative / Absolute Cylindrical (Distance, Angle, Z)
- Relative / Absolute Spherical (Distance, Plan Angle, Rise Angle)
If you are in Absolute Cartesian and enter 0, 0, 0 for the coordinate, this will in fact coincide with the drawing's origin.
When the 3D cursor is not enabled, you are working on the active construction plane which has it's own relative x, y, and z coordinates. On the 3D Menus, 3D Views, Controls menu, there is a Reset option to coordinate the construction plane origin and snap grid with the Ortho (Plan) view. This is where you'll also find the option to set the viewing center.
When the 3D Cursor is enabled, you can also use three-dimensional Object Snapping. When the 3D Cursor is off, you are snapping to the construction plane.
If you create three-sided polygons using the 3D Entity, Polygons, Inclines 3 Edge Poly, the 3D Cursor is enabled automatically. The 3D Cursor is optional when creating 3D Lines, Contours, and 3D Markers. All other 3D entities must be entered relative to the current construction plane.
I did create a video on using DataCAD's 3D Rotate Command which may find helpful.https://youtu.be/dRHSRft8wHg