Surface _SrfPt command from 4 picks dir is inward why?

Hi,
V5
If I pick a square using surface 4 points on the grid the dir shows inward, why is it made as such ?

it also does this in V7.

Am I wrong in saying a block made with surfaces has dir pointing outward ?

So making surfaces on an object with this 4point surface tool ( _SrfPt) will need surfaces flipping to avoid nasties later on.

I draw a block using block tool and yes they point outward.

I spotted this having made a surface on an existing item and it looked darker than expected. is that command which I often use dir’ing wrong ?, dir needed flipping before I joined surfaces.

Cheers

Steve

Please post a Rhino file with the geometry.

Always pick the points in counterclockwise order (in the view you want to face upwards in).

Hi,
Well I must be oddball as I draw from left to right, clockwise, etc.
I am right handed.
Its my brains default.

Thanks Helvetosaur…Ok CCW fixes the problem.

I then draw a shape planar with the line tool and use surface Planar (_PlanarSrf) tool to fill it with a surface.
As I draw clockwise, it ends up also needing a dir flip.

I think to expect folk to draw counter intuitively, esp as Rhino is a very intuitive prog, is daft.

Can one change this behaviour in properties, and make CW draw create correct dir ?

basic fundamental thing here, maybe have it as a question option during setup when installing.

I bet most folk would choose CW.

How is it in other CAD ?

Cheers

Steve

No, it’s not daft, it’s mathematics. Angles in Rhino start at 0 (+X-Axis) and are positive in the counter-clockwise direction according to the right hand rule. The basic closed curve direction follows this rule (make a circle or a rectangle in top view and check with Dir), and surfaces are derived from curves.

If you force curves to go the other way by your pick order, as it’s still a right hand coordinate system, the Z axis HAS to flip in the other direction. Planar surfaces made from curves running in the clockwise direction will inherit the direction from the curve so they will also be inverted. Etc.

Hi,
Ok its maths, however folk instinctively draw left to right,

Newcomers would do so. we just must remember to check dir on things !

I am still getting used to the fact that rotating something needs a minus value !

I am glad maths doesnt enter human basics, else we would be trying to feed ourselves at the back of our heads :laughing: and as for certain functions, best watch an episode of Red Dwarf ‘Backwards’ S3 E1… the character ‘Cat’ .in the grass ! nr end of episode.

Steve