I’ve been modelling a DB bzf 761 doppelsteuerwagen (Dostos STW) for Open Rails on and off for a while.

Lately, I’ve come across a limitation with the bezier curves which I cannot overcome with the current tools supplied within blender, and I’d like some advice on how to overcome this problem.

Currently, I’m trying to model the interior stairs of the 761 from scratch, using bezier curves as they define geometry very well, and very quickly with ease.

The problem comes up with circles.

The problem with this, would be the handles

http://wiki.blender.org/index.php/Doc:2.6/Manual/Modeling/Curves#Editing_Bezier_Curves

As soon as I modify the handles, the circle deforms and it becomes oddly - shaped.

For example: It’s impossible to create a perfect arc other then ones which are a multiple of 90 degree ones like you can do in Inkscape.

This creates problems when creating walls which arc round, using meshes sin’t that much better to use either, since you can’t achieve the precision like bezier curves can.

Another problem, would be angling with respect of the nodes.

For example: Imagine an arc along a horizontal plane, it would appear like a flat line.

And then, lets try to move the one of the nodes up.

Here’s the same curve in 3D view

Then, an Inkscape representation of the desired method:

The desired effect:

It’s not exactly possible to achieve that with the current tools without distorting the circle using rotation and scaling, which leads to inaccuracies.

Can someone help me with these problems as they’re quite hard for me to solve with the tools that I current have?:eyebrowlift: