Script to isolate or select outermost line work

[unearthed]

I often only want the outer lines of a given 2D object that I've imported., e.g. this set of roof line work where I only want the outer roofline.

 

I realise a lot of these lines cross into the inner space (and I'll need to trim them) but just getting the outer ones in a selection would remove a tedious small repeted action.

 

I want to do this with drawn elements, and items like surveyor's TINS, and also the jumble of objects that results from exploding .pdfs (where there is normally only a single layer in the drawing).

[JBenghiat]

Have you tried the outer boundary mode of the polygon tool?

 

Otherwise, you’re interested in a concave hull algorithm. You may be able to find some existing python examples, but I don’t think you’ll find a simple code snippet that someone can provide. 

[unearthed]

Thanks, I didn't know of Outer Boundary tool - It doesn't work for this, BUT it does do something else very useful  - making quick polygons from unjoined lines:

 

Even a concave gull algo may have issues (tho' I'm far from an expert) as there are self interesting lines in my case.

 

 

[unearthed]

Thanks Joshua, that's a very useful workflow - basically a flood fill but but for loose vectors.

 

I just drew a box round my various lines (they do have to be touching or crossing and form a hull / continuous closed object), and then did;

2D Tool plus Inner Boundary Mode and;

Ungroup and deleted my outer rectangle

 

No more messing around with dozens of lines/