Right, I think we need to make that "In current viewport" thing more prominent somehow.

So this is the NZ longest line right https://map.alltheviews.world/longest/173.61386108398438_-42...

One thing to note about finding reverse lines, is that they're not truly mathematically identical because the observer always has a height of 1.65m and the destination is always some point at the surface, therefore 0.0m. It doesn't always make a difference, but it sometimes can.