Hi Bartosh, so part of the overall strategy of constructing things from 2D profile curves is avoiding poor quality curves. The quality of the curves will often inherit into the 3D model structure built from them and if you have junky curves that will yield junky models.
The quality of curves coming from a 2D illustration program can often times be pretty bad. 2D illustration work can tolerate lower quality curves because they don't do as complex calculations on them as is required for filleting.
So in your case here seeing the low quality of the curves you would want to draw new ones in Moi just using the ones from the file as a reference point and then throwing them out.
> 1) I`ve noticed red squares. I can`t find what it means? I`ve deleted it and filled gaps with new curves.
Like Pilou wrote above, this indicates multiple control points from a single curve segment stacked up right on top of each other. This degrades some of the mathematical properties of the curve and should be avoided.
> 2) I`ve unjoined curve to fix it (it was build from many short curves). I`ve tried merge
> command. I`ve tried rebuild command. Without success.
Well with curves as messy as these to get best results I would recommend throwing them away and drawing new ones. You can snap a couple of points onto them to guide your new curves like I'd probably start by drawing in a few lines for the straight areas.
> 3) I`ve joined those curves once again. Tried extrude on it. All works fine. I`ve seen those short edges and I knew that will be problem with that.
Extrude is less sensitive to curve quality than filleting.
> 4) error :)
Yup, messy curves will make for errors down the road with more complex calculations. You want to start out with good quality curves to avoid that from happening.
A couple of the problem areas of these curves is the stacked up control points like you noticed but it's also split up into numerous small segments which are not smooth to each other, for example here is one spot that you can see is a line segment not smoothly connected to its neighboring segments:
- Michael