Jim,

You are expecting that Rhino’s Interpcrv command will change your tangent pick points based on what you think makes makes a better looking curve. That would involve Rhino knowing how to read your mind, so I’m pretty sure that isn’t going to happen.

Nothing about what I think looks best, When I use the straight line tool and start tan on circle it picks the best spot for the circle line to carry on into the straight line. I use the program to mathematically decide that. I seek that mathematical help with a curved line as surely there has to be a point on a circle that suits the correct geometrical placement of a line if it is to be tangential, else it will show in any render etc as imperfect.

If that straight line happens instead to be curving, there has to be a mathematical point on a circle that allows that curve to sweep mathematically correctly into the circle, not what pleases my eye, but what is geometrically correct.

I am after geometric correctness. Not just on a 2mm circle which could be sanded down, but on ANY circle for any curve.

Hi Jeff, you say:-

i don’t see how you’re expecting this to work out… the reason the sliding(?) tangent point works with a line or a arc is because there’s an exact point in which tangency will occur with the original curve depending on where the second point is placed… with interpCrv, the first tangent point could still happen anywhere along the original curve regardless of where the second point is placed…

there wouldn’t ever be a correct place along the original curve for rhino to slide the tangent to because any point on the curve will work

Any point wouldnt work though, as I head off out through my points clicking away with InterpCrv the curve shape alters at first and the further away I go the less it then adjusts for the first few points, my arbitrary pick on the circle needs to be able to move to choose the best location for the end of my curve to flow GEOMETRICALLY CORRECTLY into that circle, as opposed to what my eye fancies. Rhinos final choice being made when I right click and end the draw.

there’s an exact point in which tangency will occur with the original curve depending on where the second point is placed…

If we take a curved line and marry its end to somewhere on a circle, is it geometrically not possible for there to be a unique spot on that circle for that curved line to be tangential to a circle ?

AIW depending on what this is about, and how big circles might be, yes to brush aside this need, one could sandpaper the aluminium sheet down, not sure if it would break there in flight though, but I dont wish to brush the dirt under the carpet, I wish to consider any circle, not just a 2mm rad one, as this need will arise again on something different.

I used Pascals suggestion of trim curve at last point before trailing edge, make a new line from that point to Circle snapping on Tan.

Match command the line to the trimmed curve for curvature and preserve other end is set to Tangency, apart from two picks of the line needed to get the options to appear !!!, the command then proceeds to nuke half my line ! V4 and V5…doh !!!

Jim

In the enclosed file shows how you might get the curve you want. The two red lines are drawn as helpers. The red lines are tangent to the circle with the other end about midway from the two start and end points in your original interpolated curve. The cyan curve is what you get using this method.

Basically like I did, you use the straight line tools Tan from curve ability in a snap to tan way instead of start on tan, or does such option in fact see a difference in the tan line ?

For my equivalent of your red line I went from circle to first point, you have gone for midway from circle to first point snapping on tan. Was the midway choice your own idea or a mathematical likelihood of better fit ?

Did you then use interpCrv and choose start tangent or just start on the end of the line and head off through my points ignoring the other end of your red line. I tried the latter but my curve doesnt quite fit yours so I guess yoy did start tangent. Trying that it as good as fits yours. Maybe the amount I pull the tangent out varies it.

Steve