Able to flip loft, but not sweep

[eobet]

When I loft between two curves, I can change the surface orientation by changing which end of the curves I click on.

I’m not able to do this with sweep:

Note how the bottom sweep is red (which indicates a rear facing surface in my view mode).

I’ve also even used Flip on that curve and it made no difference.

Why is the behavior here seemingly different from loft curve selection?

sweep-surface-orientation.3dm (278.1 KB)

I’m also a little bit curious as to why my resulting surface has 19 points along the sweep curve even though I chose to not refit…

EDIT: Turns out, there’s a similar issue with sweep2… no matter how I click, I’m unable to alter the surface orientation.

[Tom_P]

Dear @eobet
after surface creation use the
_dir
command to get the needed UVN / surface-normal direction.

(some edits below…)

loft

I thought there is some logic how the UVN direction is determined - for a loft - but i did not find any.
clicking on each single curve - the pick-point has some influence.
selecting by layer / or object name - I do not see any logic…

sweep1

if there is only one shape / cross it seams like the curve-Direction is not important, but the “right hand rule” is applied - based on the shared point of rail and shape shape.

looks quite predictable…

sweep2

looks like the first rail and the first cross / shape define the orientation in similar fashion as sweep 1

also looks quite predictable…

[eobet]

@Tom_P

after surface creation

That breaks history, though, which is why I made this topic.

[Tom_P]

@eobet

history

why do you need an orientated surface ?
why does the normal direction matter in your workflow - what is the next step ?

see my edit above - using sweep1 and sweep2 - i get predictable results for a surface direction.

building your surface in question, using sweep1
this is my guess how the normal direction is defined
u/x orange
v/y green
n/z blue

starting a _sweep1 from the other end will give opposite normal direction - with the same right hand rule: