Rules about Building
There are certain rules that must be obeyed when building surfaces:
- For certain mathematical reasons, the projection curves must always
be B-splines. (Section curves may be either B-splines or Béziers.)
- All projection curves (including the secondary curves) must have an equal
number of control points. Adding a control point to one projection curve means
that a similar point must be added to all other projection curves.

- There does not need to be an equal number of points in each of the section
curves. However, if sections have unequal number of points DeskArtes will convert
them before building so that they do have the same number of points. This automatic
conversion may not be ideal so you may prefer to create all sections with equal
points. It is usually best to start modeling the section curves with the most complex
then the simpler ones.
- In order to avoid twisted surfaces, all section curves must have their starting
points aligned. Likewise, they must be oriented in the same direction
(clockwise or counter clockwise).

- When editing a secondary projection, DeskArtes will only allow you to move the
control points in one direction (the direction of the primary projection).
Without this restriction it would be possible to have conflicting information between
the primary and secondary projection curves.