# Boolean Difference to create Path along Topography

Hello everyone, first of all, this is not a topic about boolean difference failing. Its more of a geometrical problem I am having a hard time resolving. This follows:

-I have a topography.
-Then I created some depressions by projecting curves. These depressions naturally are at different heights because of the topography.
-I then extruded them to allow visuals of those depressions.
-This created “steps”. So now I want to connect these depressions with a path that follows the topography, eliminating these steps.

Problem: These steps have different heghts and I dont understand how to eliminate them following the topography.

Straight bases and steps as consequence.

Path connecting these straight bases.

Stuck. Here the boolean difference would not create a topographical path, as the base of those volumes is straight.

I hope I have been clear enough. Thanks for any insight.
Attached file with all solids and procedural steps.
Shynn

Procedure for Path.3dm (4.8 MB)

Hi Shynn - I guess to get the path surface you can offset the main topo surface down a little as a start and trim out paths from the result - is that something like what you are after?

-Pascal

Hi Pascal, I am afraid I am not entirely understanding your suggestion.
I added a section sketch so represent the idea.
The original one shows the steps.
The new one would be the new section after the boolean operation, the steps are now eliminated and the straight bases are connected by the natural topography.

Kinda like this (this was done entirely manually and moving control points of a dup border curve)

Hi Shynn - maybe I am misunderstanding what you’re after - I just thought that to follow the topography, the basic path surface should be an offset of the main surface.

-Pascal

Mmm maybe an example of what you suggest could help, maybe you are right and Im just not seeing it.

Hi Shynn - I really don’t know if this is on the right track, but:

Green= a piece of the topo surface
Red = Offset downward
Blue = your object minus the red surface (BooleanDifference)
Black is cut out with the blue object and has a ‘path’ that follows the topo. The ends are unclean of course, but maybe that is what you’re after, apart from that?
Procedure for Path_PG.3dm (1.2 MB)

-Pascal

Thats the right way, but the ends are intended to be stepless, on both sides.

Red marking where the floor should start.

Hi Shynn - right, the ends will have to be handled with separate ramp surfaces - otherwise I don’t see how you can follow the topo for most of the path.

-Pascal

Mhmm thats nos ideal, do you think its geoemtrically imposible then?

Hi Shynn - I would say that it depends how closely you want to follow the topology - you could make a blend surface between your cuts and trim with the vertical sides of the path, if that is good enough:
Procedure for Path_PG2.3dm (1.3 MB)
?
-Pascal

I guess I was looking for a “perfect” way of doing it following the topography 100%.

But this result is totally okay. Care to explain the procedure once again?
You made two planar surfaces. Blend them, resulting in the cyan surface. Not sure how you got the red one. Or the white solid to finally do the boolean difference.

Thank you