I should clean segmented bitmap of course, and acceptable connection should be possible without any knowledge about z-value or else nor caring about gap size or curve density. As I mentioned, there are couple of reliable methods reported, some dating decades ago. Here is for example one method, I noted above: http://iparla.inria....04/SG04/K13.pdf
On paper, there are also methods by using b-splines, FEMs or some most obvious ideas if you think about this problem as:
- do spline fit on existing lines and connect all gap points within certain radius,
- find some sweet spot depending on connected curves direction angle and connection line direction angle
- decide which connection line to keep
This is simple enough, but why can't similar method be found in GIS software?
Even GIS flagship gdal doesn't offer such functionality, not mentioning expensive commercial applications like ArcGIS (to try it, I had to contact friend to get access, as I surely can't afford the license)
OTOH, if I should look in image processing tools I have to choose something robust enough as curve reconstruction is such niche.
I plan to go with Python, if I can't find ready-made tool.