Hi Michael,

Having closed paths is critical to several common tasks in technical illustration:

1. Closed outline curve so that the outline stroke can be aligned to the outside of the path rather than along center. This avoids having a thick outline overlap the inside of an object which is important when there are fine details along the outline.
2. Hatching clipping mask like for adding a hatch pattern to indicate that a face has been cut by a cross section plane
3. Fills such as block shading like this example:
   
   https://moi3d.com/forum/lmessages.php?webtag=MOI&msg=10770.1
   
   which was made by hand in a vector graphics editor by drawing closed curves and then filling them.
   

Needing closed paths has come up before:

https://technicalillustrators.org/forum/viewtopic.php?f=1&t=211&start=7

http://moi3d.com/forum/lmessages.php?webtag=MOI&msg=6201.61

I've tried out a bunch of different ways of getting from the MoI's SVG/AI output to closed paths, but have found that Illustrator's Live Paint is the only one that works reliably. Several other vector graphics editors claim to have this capability, but they aren't reliable on MoI's vector output because of tiny geometry problems that are essentially invisible. Inkscape is reliable, but sometimes leaves a gap between the closed shape and the line art, and has other problems.

So, it would be helpful if another layer were added to MoI's SVG/AI output. This layer would contain nothing but closed paths.

A few approaches that might work:

• GMIC colorize line art: https://www.davidrevoy.com/article324/smart-coloring-preview-of-a-new-gmic-filter
• Expand strokes into filled shapes, boolean union, extract the resulting closed curves, and then offset them to give some bleed
• Rasterization followed by vectorization like Inkscape “Fill Bounded Area” followed by offsetting to give some bleed. But there are problems with this: https://wiki.inkscape.org/wiki/index.php/A_better_Bucket_Fill_tool_fill