Crop closed paths into open paths

Question

In a few operations, how can I crop closed paths and have the result be a set of open paths? It's important that the solution be as few operations as possible, and not rely on point and click. (I'm looking for something scalable to perform operations on very complex map images.)

Someone asked the same question here: https://www.reddit.com/r/Inkscape/comments/75xjfa/intersection_with_open_paths_or_equivalent/

Here's a very simple example of the objects I'm starting with:

The orange area is a closed path that I want to crop to, and the black lines are a bunch of closed paths that I want to be cropped. This is what I want the result to look like:

The lines must be open in the final result. That is, each line is just that - a line with no fill. (Ideally, they'd keep the stroke I've set initially, but not required.)

It's important that this solution applies to much more complex scenarios too. For example, I'd want to crop the lines in this example down to the purple areas:

The images I'm working with are extremely large, and can have thousands of islands to crop out. (Point and click with a mouse to delete paths won't work...)

I'm open to using any software available, but I'd prefer something open source / scriptable. Illustrator or Inkscape would do.

Answer 1

In Inkscape, as long as the curved parallel lines are a compound path, and the squiggly shapes are another compound path on top, then you can use the Path > Cut Path boolean operation. However the operation will consume the upper path, so if you want to keep it, copy it before you do the Cut Path, then Paste in Place after you've done it.

Example, before (left), and after manually deleting the cut paths (right).

Answer 2

One (Illustrator) method...

With the art you have...

• Select all
• Grab the Shape Builder Tool
• Hold Down the Option/Alt key and click-drag across the lines outside the rectangle to remove them

(After question edit) -- This will work for all your shapes. Just select all and then Option-Click-Drag with Shape Builder to remove what you don't want.

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Another (Illustrator) method....

• Move (or copy) the rectangle so it is on top of the paths.

• Select the lines and this top rectangle.

• Click the Divide button on the Pathfinder Panel (Window > Pathfinder)

• Simply delete what you don't want.

Answer 3

You have this:

Select all, apply Pathfinder panel's Outline. You get this:

Every path is split at every crossing, all colors are removed and all is grouped.

Ungroup, select the wanted parts and copy them to the clipboard to keep them in safe.

Select all, Delete, Paste in Place the content from the clipboard and insert some stroke color and thickness to get this:

ADD after the question was edited:

The presented method is quite useless if there's hundreds of shapes for the areas which are wanted to stay. In this case I recommend to use them as a clipping mask. Select the colored shapes for ex. by using Select > Same > Fill Color, make an union and use it as a Clipping Mask. It only makes the unwanted parts invisible, the curves between the islands are not deleted. By using a clipping mask one can make the following:

If the intermediate parts of the black curves must be deleted you can expand the black curves by selecting them and applying Object > Path > Stroke to Path. They can be made to one by applying Object > Compound path > Make.

The pink islands can be selected (maybe by layer or the same color) and also combined to compound path.

The visually right result is achieved by applying Pathfinder panel's Intersect. But the result is a group of expanded strokes which are thin closed shapes, not simple open curves.

The same can be got by expanding the curves which have a clipping mask and by applying pathfinder panel's Crop.

If you are a programmer you surely find a way to remove or ignore the unwanted parts of the expanded curves.

Answer 4

Let's start with this... Notice that shapes used for trimming are in front of objects that need to be trimmed.

Select All then apply Pathfinder / Outline.

Ungroup everything. Select any line that doesn't have any stroke (those are the lines outside of trimming areas). Then select objects with same stroke color and delete them.

Now, we are left with ALMOST what we need. We should still get rid of the lines of original trimming shapes. Here I have changed the width of the strokes so it is more clear. On the Layers palette we can see that all of these lines are on top of all others.

We should locate the first one that is not on the edges:

Now, just select (in Layers pallete, using Shift key) all above it and delete them through Layers palette.