Full Version: Does Curve 3 points show Tangent mode?

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Hello folks, I faced a problem. Please take a look at the attached photo.



I drew the red line as you could see and I want blue curve ( Curve 3 points) to be tangent with the red line! Unfortunately MOI does not show the tangent point! Or maybe I am doing it wrong. Would you please guide me through?

Needless to say that Snap modes are on!

Attachments:
J_Screw.3dm

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Seems the inverse but maybe this can help you :)
Little trick to find the Apex of something!
(the outermost point of something)

Draw a small vertical line around the supposed point!

Then draw a Point coming from the middle of this vertical using the "Helper Lines": Perp / Perp

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Dear Pilou,

I love 2D & 3D Geometry and I can say I am familiar with it to some extent :)
However, as you mentioned it is inverse of what I want! the line is fixed! I want the curve to be tangent to the line and of course I seek a simple method in which one should not go through geometric calculations to find the tangent point ( although it could be fun :)

So, in MOI 3D, when you already have a line how could you draw a curve tangent to that line, quick and fast?

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Hello Chris,

What did you mean by "." ?

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GIF is not yet admissible by the forum ! (technical problem)
So be patient :)

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Excuses me Psygorn

i have try somethink but it does not work

then i have try to delete my post

i continue to search

Chri

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So you have the tangent point on red line you want (the 1.75)?

Off the top of my head, the "easiest" would be to draw 2 curves, split at the tangent. (Tangency maintained by the first 2 pick points of a cotrol point curve)

I am away and on my phone. CN explore curve tools when i get home...

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Hello dear,

I don't have the Tangent point yet! I want to find it! :)

I have the red line (1.75 millimetres away from the main axis) and start and end point of the 3_Points curve at 2.16 & 2.50 respectively then I want to be sure that the 3 points curve ( blue curve) is tangent to the red line!

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When you say Curve 3 Points, you mean Arc 3 Points ?
Because if it's a curve you have an infinity of solutions!

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Hi Psygorn, may be you can do it the (not so) hard way with 3pt circle ?

Attachments:
Untitled.mp4

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Sorry my bad! yes you are right I mean Arc 3 points. :-)

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Your method sounds promising, However, I have to check it thoroughly. ( I mean I want to check if it yields true tangent point) needless to say it sounds promising.

One thing that made me suspicious about it is that when I zoom in I see two different crossing! ( I mean when I zoom in it seems the curve crosses the red line at two different points which means this method does not show the true tangent point)

I checked it using Trim method and it seems your method is correct way of finding the tangent point!

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Hi Psygorn so if you do mean "Arc through 3 points", 3 non-collinear points already fully defines a single unique arc and so there isn't any way to set up a tangent additionally there.

I'm not sure that there is a built in tool in MoI currently that will generate a circle by tangent and 2 points on the circle. It can be calculated with this method:
https://www.emathzone.com/tutorials/geometry/equation-of-a-circle-given-two-points-and-tangent-line.html

- Michael

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I'll be the first to say I'm not good at geometry. May be a simpler way.

This does seem to match your blue curve. Coincidence? Will it work in all cases? Don't know :)

Draw two small half circles (magenta)

Draw straight line to ends of circles (green)

Select both circles and Blend [Tangent G1, Bulge = 1] (cyan)

Pilou find apex trick (orange lines)

Draw Perp to Perp line from Blend apex to green line (black)

Draw 3-point arc from top to bottom of green line while snapping the center to the intersection of the black & red lines (blue)

Ed Ferguson

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Perfect maybe...
So my little trick can help! :)

A curious problem who can have some solutions! :)

A perfect headache!

PS Alas your method don't work :( Big zoom shows 2 crossing curves!
Or i miss the verification...

Little half circles are well on the same line than the green one ?

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The Circle tangent command can do circle tangent to 2 curves through a point, or tangent to 3 curves, but not tangent to one curve through 2 points like you want in this case.

- Michael

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Hi Psygorn,

re:
> So, in MOI 3D, when you already have a line how could you draw a curve tangent to that line, quick and fast?

Circle Diameter can make a circle tangent to a line quick and fast, the problem is that you want not just a tangent circle quick and fast but also passing through 2 points.

- Michael

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OK I believe i have found! :) Half only ! :( so...on the track!

And with my Apex trick! ;)

Just draw a little red arc circle 3 points! :)

Resists half to the big zoom! :)

Damned! It's good just on upper part! :(

https://moiscript.weebly.com/uploads/3/9/3/8/3938813/resist.3dm

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What a fight!
With a little red, a big black, intersection with the 2 Apex on the green Vertical
quasi perfect but...the black arc is not totally under the green one always on the bottom part at atomic zoom size! :(

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