Usually, a pattern can be defined by its two ends.
For example, your transition may be defined by two polylines e.g., an irregular pentagon as the base [end 1] and an oblique ellipse as the top [end 2]. It is easy to generate both in AutoCAD or GStarCAD.
Place them in your CAD's 3D space according to your needs.
Start LITIO 2.0, choose this option [Free pattern from two 3D curves], click on both entities, define some few parameters [thickness and internal fillet radius], and you get the resulting 3D
developable surface [if it 'mathematically' exists] and its development.
You can create transitions just by clicking any two valid entities (either 3D meshes created by Litio 2.0; or 2D and 3D
polylines; or circles, located in AutoCAD/GStarCAD's 3D space.*
Thus, LITIO 2.0 gives you much more transitions than the ones available through its standard dialogue boxes.
* Some restrictions apply [see user manual]. Note, that the following entities are not accepted: arcs [convert arcs to polylines using the PEDIT command] nor ellipses [use ellipse pattern of LITIO 2.0], and resulting 3D objects cannot have concavities.
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Advanced features case study: How to make non-standard customized transitions using free transitions special feature of LITIO 2.
Types of entities that can be picked to create free transitions: 3D meshes
created by Litio 2.0; or 2D and 3D polylines; or circles, located in AutoCAD's 3D space.
Remember that resulting 3D objects cannot have concavities.
The following entities are not accepted: arcs [arcs need to be converted to polylines using the PEDIT command] nor ellipses [ellipse pattern of LITIO 2.0 can be used].)
Transition is created.
When seam position is a concern, free transitions can be made from sectors of polylines.
For entities situated on parallel Z [zet] planes, corresponding ends shall have their tangents at the same angle. For arc segments it means, that corresponding ends start or end at the same angular positions. Polylines are shown here in different colors for better understanding.
Video shows all this process and photo of actual object. Hosted at