Grasshopper

algorithmic modeling for Rhino

I am sure I had this problem before, but cant find the solution anymore.

I have a curve, which is a rotated circle in this case and use Perpendicular Frames to get a local plane at different points along the curve.

What I noticed is that in some cases the X and Y axis is flipped, but seemingly with no logic to it. I also noticed that if the circle is upright, the top half has Y pointing outwards and the lower half inwards.

How can I get reliable planes that have consistend direction?

Thanks, Armin.

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Daniel, thanks for your quick answer. Maybe I should have specified more clearly, but this only works with a flat curve, but should work with any 3-dimensional curve, where the Y-Vectors are not all pointing in the same direction. I am not 100% sure what I have done, but it seems to be ok now. I think it might have something to do with "Rebuild Curve", which I was using, but not anymore. 

Still I think its a bug, that sometimes planes are flipped 180 degrees and I remember I made a workaround for it, but cant find it anymore. I think something like you just flip all of them, combine the list of flipped and non-flipped then sort and take the first half of vectors, then use the Z-Vector (which is the same, even when it is flipped) and recreate the X-Vector!?

I am interested to know WHY it flips sometimes though.

How do I make all of these planes face up?

It's a bug. Not sure whether it can be fixed before Rhino6 ships, but it's on the list now:

https://mcneel.myjetbrains.com/youtrack/issue/RH-41494

Glad to see this is on the list, (still) tho I think it says that the issue probably won't be addressed until sometime in 7.x?

>I'm curious what workarounds folks are using for this?

Example: "torqued obelisk": where cross-sect structural members are extruded along lines, using 'Perpendicular Frame' & 'Orient'.  At certain junctions, the planes flip (or I assume they do as the structural members flip out-of-alignment). 

I tried generating the structure 2-ways to see if it was just me --using curves w/ endpoints (left) and culled-subSurface-edges (right).  The location of the "flip" seems to be dependent upon the rotation of the generative squares (3 arrayed vertically & rotated @ 0, 30, & 60 dgrs) as well as the derivation method, but I can't seem to negate it all together.

Surface orientation as well as curve direction all seem to be uniform...

>GG *might* be a workaround...

RH 6.15.19141.8361, 05/21/2019

GH 1.0.0007, 2019-05-21

Win7x64 Pro

Thx in advance,

-dt

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