How to draw some tangent lines on a 3d shape?

[ahad (je park)]

hi all
I hope all is well.
I gonna draw some tangent lines on my 3d shape. in order to determine slope angle (determine a & b). could u please tell me, how can i do that?

@pascal

[pascal (Pascal Golay)]

Hello - I cannot tell if that us a mesh or a surface - if it is a mesh then you can use Line > Extend to make ‘tangent’ lines. In V6 you will need to ExtractWireframe first, to get the polygon edges as lines, V7 can extend an edge as a line directly.
if it is a surface, use either the edge curve (if it is a revolved surface) or Silhouette to get a curve and then use Line > Tangent

-Pascal

[ahad (je park)]

AliHamzeBESTbestECOTECT.3dm (560.0 KB)

dear @pascal
I guess, this is a surface, then i use Silhouette and then line>>tangent
but happen nothing unfortunately.

best

[wim (Wim Dekeyser)]

Hi -

@ahad

but happen nothing unfortunately.

Could you explain what that means? Doesn’t the command start? Don’t you get the Start of line prompt? If you do get to the End of line prompt, make sure not to wander off from the silhouette too far.

Note: you are running Rhino 6.13 and should update to the current 6.27 version.
-wim