How can I draw this curve so that the starting point is at 200 and the end point is at 400?
The radius should be 500. From above, the lines must be on top of each other.
The “apparent” radius can look the same from the top, the the upper curve can not have the same radius and the lower curve, because it’s longer.
You need a segment of a helix.
Does your upper curve have to be tangent to the tops of the boxes or is a kink okay?
What I might do:
- Extrude the two arc surfaces to the full height (400)
- Make a BlendCrv (Tangent) from one edge of the lower box to the corresponding edge of the upper box
- Pull the curve to the inside arc surface
- Pull a copy of the curve to the outside arc surface
- Trim each surface with its curve
- Sweep2Rail using the two top edges of the trimmed surfaces as rails, and the two edges of the boxes as profiles
- Trim, Join, Cap etc. to create solid
RampExample.3dm (2.5 MB)
Kink where?
Imagine that the front and rear surfaces are the formwork. I then fill it with concrete and use a wooden slat to pull the concrete off the top along the curve.
Wow, thanks.
Well, if you use a helix as John mentioned you will get a constant-slope ramp with an abrupt change in angle (fold, kink) from horizontal to the ramp angle at the bottom and again back to horizontal at the top. I assumed this was some kind of walking path and that there should be a gradual change in slope starting from zero at the bottom, having a maximum slope in the middle and flattening out at the top. There are endless variations on how fast this transition can be at either end.
Having a constant-slope ramp using a helix is not aesthetically as nice and may not be as comfortable to walk, but it could also be used as a basis for modeling a spiral stairway…
RampExample2.3dm (2.9 MB)
Hello - I think, I if I reading this right. what I’d do here is take the true arcs as they are, ChangeDegree to three, to get four control points, and then move the two points at each end in Z to the start and end levels.
then make lofts to connect
This way in plan the arc stays true, if you see what I mean.
-Pascal
3 Likes
What exactly do you mean by the end levels?
Except it’s difficult to get it to conform exactly to the arc radius in plan view if that is the intent.
You’re right. It is way off from r 500. So that’s not the right thing to do.
With the blend handles you can adjust it so it’s close (assuming tangent both ends is checked) - but it will never be as exact as the previously outlined method. Also, the path does seem to get a bit thinner (less wide) in the middle.
Pascal’s method of using the arcs and ChangeDegree is also very cool, may even result in a nicer transition from flat to sloped.
Can you take a screenshot, e.g. a gif, of your solution? I can’t reproduce this.
ShareX or OBS
Which one? There are a couple of Rhino files posted above…
No, of yours.
The .3dm file is in that same post and separated into the steps I outlined, different parts are on different layers. What part are you unable to reproduce?
You need to use the long edges of your boxes for the blend, not the short ones…
It worked.
Just to understand the whole thing. It’s true that you have to position this line with a sense of proportion, right? Projecting the line (Curvature 1,2) onto the surface is not possible or it would be mathematically incorrect?
PS: This solution is good for my purpose.