Osnap Tangent Option


I was wondering if someone might be able to comment on ‘proper’ use or limits of the osnap tangent option.

To keep this post brief on why I want to use the tangent option as in my attached file I’ve simply done a simple version just for illustrative purposes. Because in the file I’m including there are many other options to get the intended result.

In this file I’ve drawn a curve in Top view with cplane set to World Top.

After which I’ve drawn a vertical line not connected to the curve.

Setting osnap options to near and tangent my hope is that I will get the point ( any point along the vertical line actually ) to snap to part of the curve that is tangent to that vertical line.( keeping that line vertical in the process ).

By observation and knowing how I construction the curve I know where the position of the tangent should be but the osnap tangent most of the time doesn’t give me the results expected.

In my file I’ve left the vertical line at the most recent point where Rhino indicated where the tangent point is. Clearly it isn’t.

To add to the strangeness if I move the vertical line off the curve someplace else in the view and deselect - Then reselect and try again, Rhino will give me a different ‘tangent’ position along the curve than what it did before.

Comments that help me understand this is appreciated - Thank You

Tangent to a curve.3dm (24.7 KB)

Hi BabaJ - so, you are looking to Move or drag the line to be tangent, correct? That makes some sense but is not how Tan OSnap works - rather, in making the line, you’d place a start point then with Tan place the end point on the wiggly curve so that the line is tangent to the curve there.


Yes that is what I would like to do.

I’ve tried what your saying, and just tried it again…but the problem is, to get it where I want I have to know beforehand where exactly that tangent point is before I can start the line directly vertical to it

So, Pascal, are you saying Tan Osnap is designed to make the 2nd point of a line tangent where it can, given that the first point is determined by some other means? It seems that you are also implying that it will not work for the first point even though it would seem perfectly natural to expect that if you used Tan Osnap for the first point of a straight line that your choice for the second point would be constrained along the tangent line and could use some other appropriate Osnap somewhere along the tangent line to determine the 2nd point. Is that about right?

Maybe something for the wish list if it’s not there already. Would be very handy for straight lines, but probably difficult or inappropriate to implement for anything else.

To further the discussion…I guess in this file if possible in the view find with some command I don’t know…the most extreme point along the curve to the right. This would represent 1 of 3 possible tangent points along that curve for a line vertical to the cplane, the other two could be accomplished by doing a split of the curve to isolate the other tangents

Hi Al - use TanFrom (one-shot osnap) to make a line tangent from a curve. First point with Near, say - Point will find the first point picked then inside TanFrom- admittedly a little convoluted… You can also use TanFrom for the first point in the line (off the curve someplace) and Tan for the second one, that’s on the curve.


Hi Pascal,

Maybe I am misunderstanding you, but I still need to be able to know where to pick that initial point that gives me the result I want.

Otherwise I’m only estimating.

Hi BabaJ - if the line is vertical (or in general, Ortho to the CPlane), then the start point can the the Quad osnap on the wiggly curve - is that what you mean?


Hi Pascal, I don’t know…I’m going to play with that for a bit.

For the example file I provided its works, but I’m not sure if it will for other circumstances.

The different circumstances would be where I create a user cplane looking at an object from a specific ‘real life angle/view’…and on that new cplane project the object onto the cplane and make new objects based on specific starting points that are tangent along the curve of the object that was projected.

I know this sounds convoluted, which is why I opted for the simpler example.

But I will go back to my part of the project where I need to do this and do a search the quad option to understand technically what it is ‘suppose’ to do.

Thanks for your feedback

Ok…so I just tried it on one of my examples…and it works…so I looked up the description…

“…Snap to the point on a curve that is at the maximum x or y point relative to the current construction plane…”

So it looks like I’ll be able to use this in most cases…I guess never thought of using it since to me the word Quad was implying something else to me.

So thanks again…I’m back on track :slight_smile: