v2 SimplifyPaths vs. v1 CleanPolygons & SimplifyPolygons

[ramcdona]

Thanks @AngusJohnson for all the work on this library -- and to anyone in the community who helps other users.

I'm porting my program from Clipper1 to Clipper2.

I use Clipper to calculate projected areas of 3d meshes. To do this, I rotate the 3D model such that the X-direction is aligned with the desired projection direction. I then smash all the triangles into the YZ plane. I use Clipper to take the Union of all those tris. In a typical case, there can easily be tens or hundreds of thousands of tris. The result is a polygon around the perimeter of the projected area.

Sometimes, part of the boundary is a straight line, but because of the process I take to get there, it is usually made up of a large number of segments.

With v1, I would call

CleanPolygons( sol ); SimplifyPolygons( sol );

After my big Union operation. This would do a nice job of cleaning up the result to a minimum number of segments.

What is the best way to achieve similar results in Clipper2?

Should I use SimplifyPaths?

I see RamerDouglasPeucker which the documentation makes it sound like I should avoid.

I just found PreserveCollinear which seems to default to true. When I set it to false, it improves things, but not as aggressively as I would have expected.

I've also found TrimCollinear, just to keep me on my toes. For now I'm using Clipper64 (i.e. no tolerance specified for these), TrimCollinear after PreserveCollinear=false makes no difference -- makes sense.

If I use SimplifyPaths or TrimCollinear along with ClipperD, what tolerance should I use? I.e. is that tolerance in the model scale that I provide the points in, or in some other scale?

Thanks for any suggestions.

[AngusJohnson]

Sometimes, part of the boundary is a straight line, but because of the process I take to get there, it is usually made up of a large number of segments.
With v1, I would call
CleanPolygons( sol ); SimplifyPolygons( sol );
After my big Union operation. This would do a nice job of cleaning up the result to a minimum number of segments.
What is the best way to achieve similar results in Clipper2?

Make sure that your Clipper64 object has PreserveCollinear = false.
That should be all you need, though occasionally a repeat Union operation might further simplify your solutions.

Should I use SimplifyPaths?

This function is mostly useful when offsetting.
Nevertheless I guess it could also be useful if your clipped paths have greater precision than required.

I see RamerDouglasPeucker which the documentation makes it sound like I should avoid.

Again, this function is similar to SimplifyPaths and wouldn't normally be useful following pure clipping operations.

I just found PreserveCollinear which seems to default to true. When I set it to false, it improves things, but not as aggressively as I would have expected.

OK. (As you can see I've only just now read this far 😜.)

I've also found TrimCollinear, just to keep me on my toes. For now I'm using Clipper64 (i.e. no tolerance specified for these), TrimCollinear after PreserveCollinear=false makes no difference -- makes sense.

Yep. Just use PreserveCollinear=false 😁.

If I use SimplifyPaths or TrimCollinear along with ClipperD, what tolerance should I use?

As above, just use PreserveCollinear=false.
Effectively all ClipperD does is create a wrapper around Clipper64 and convert the paths to integer coordinates before clipping (using the specified precision). So PreserveCollinear is just checks for collinearity in adjacent (integer coordinate) segments.

I.e. is that tolerance in the model scale that I provide the points in, or in some other scale?

It would probably be least confusing if you did your own scaling (ie use Clipper64 rather than using ClipperD).
So tolerances would relative to integer values.

You shouldn't be getting collinear adjacent segments when PreserveCollinear=false.
But if you're wanting to avoid near collinearity, then SimplifyPaths should help.