Turning world locations into relative (local) locations is quite simple. If you’ve got point 1 that is a world location and a point 2 that is relative to the first point, but all you have are world locations. You just subtract point 1 from point 2 and the result is the relative location of the the second point to the first point. (see blueprint)
But if you need a rope between two points you could also consider using a cable actor between those two points. The only problem is that it does twitch a bit when it spawns, but you can fix that by increasing solver iterations and/or maybe turning it invisible for a frame or two when it first spawns. You can also set the length if you want and make it short for a stretched tight rope or long for it to sag. Edit: cable components can be attached to objects and you don’t have to manually set the locations per tick yourself.
Or another alternative would be to use a beam particle effect ( A new, community-hosted Unreal Engine Wiki - Announcements and Releases - Unreal Engine Forums ) with source and target tangents at 0, and no noise modifier, so it’s just a straight line. Which is really simple to set up, you just have to add the particle system and set the source and target points in world coordinates, kinda like this:
