Tangent from circle

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 From:  manz
2788.1 
I thought this had been brought up before, but cannot find any ref.

I see no way to create a line from on a circle "Tangent from" to a remote point.

To explain, if I have a circle, start a line from on the circumference, I get various snap points, such as perpendicular, but no tan unless the next point on that line is going to a tan point on another circle/arc/curve (tan/tan).

Am I missing something, or is it just not possible?


- Steve
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 From:  jbshorty
2788.2 
you can start a construction line from the end point, and then find the tangent intersection on circle, and then draw the line...
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 From:  manz
2788.3 In reply to 2788.2 
Hi,

I am not looking for a construction workaround, just looking for a snap "from tan". Maybe the Tangent snap should be renamed to "To Tangent"?
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 From:  Michael Gibson
2788.4 In reply to 2788.1 
Hi Steve, you'll want to have Straight Snap enabled to draw a line tangent from a point on a curve.

With it enabled (highlighted in orange in the bottom toolbar), you can then get a tangent tracking line from that point. If you don't get one, then check to see if you have possibly disabled tangent snapping under Options > Snaps > Straight snap options.

Here's a demo of how it works:




If you want to make a tangent line that passes through a specific point, then in that case you start at the point and use Object Snap to find the tangent point on the curve, like this:




Then the other type of tangent snapping is that double tangent one that you saw - that's when both the start point and the end point are on curves, and there is a line of shared tangency somewhere in the general vicinity of both points. This snap not only snaps the end point of the line but also adjusts the start point of the line as well. Usually the target point that triggers it is found slightly to one side of the single tangent snap like this:



- Michael

EDITED: 18 Jul 2009 by MICHAEL GIBSON


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 From:  Michael Gibson
2788.5 In reply to 2788.3 
Hi Steve,

> Maybe the Tangent snap should be renamed to "To Tangent"?

Well, pretty much all the object snaps are "To" points...

For example End snap snaps on to an end point of a curve, Mid snap snaps on to a midpoint of a line, etc...

Tangent Object Snap snaps on to tangent points on a curve that are calculated by the line from the previous picked point to the curve.


If you want to track along a straight line, then that's what Straight Snap is for - it will do lines in axis directions, tangents, perpendicular, or surface normals.

- Michael
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 From:  manz
2788.6 In reply to 2788.4 
Hi Michael,

I do have all snaps enabled, but no "from tan" snap showing. I did check a number of times before posting.

There must be a problem with my setup. I will need to check.
edit
I have attached a vid of what I am seeing (xvid)

EDITED: 3 Aug 2009 by MANZ

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 From:  Michael Gibson
2788.7 In reply to 2788.6 
Hi Steve, hmmm that is odd, you are supposed to be getting a tangent snap in there where you were expecting to see one in your video.

Can you please post a screenshot of what your options look like under Options > Snaps ?

Maybe there is some combination of settings there that is not being handled correctly.

If I can replicate your settings over here I can see if I can reproduce the problem.

- Michael
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 From:  manz
2788.8 In reply to 2788.6 
Hi Michael,

There is a problem with my ini file, as after removing it the "from tan" snap works, if I replace the ini file, then the "from tan" does not work.

I have only just set up all the shortcut keys, I will have to start again with a new ini file.


- Steve
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 From:  Michael Gibson
2788.9 In reply to 2788.8 
Hi Steve, if you still have your old .ini file that does not work, can you please post it or e-mail it to me at moi@moi3d.com ?

I would like to take a look at it to see if I can figure out what might have gone wrong with it.

- Michael
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 From:  Michael Gibson
2788.10 In reply to 2788.6 
Hi Steve, just one more note on this,

You wrote:

> I do have all snaps enabled, but no "from tan" snap showing.

Just to clarify - in the video you posted, the settings that you popped up are actually a portion of the "Object Snap" settings, which are on that shortcut menu that pops up above the Object Snap button.

Like I mentioned before (http://moi3d.com/forum/index.php?webtag=MOI&msg=2788.4) the settings for what you are looking for in this case are "Straight Snap" settings.

For those look under the main Options dialog, under Snaps > Straight snap options.

You may have had Tangent snapping disabled there - here is a screenshot to show you where I'm referring to:



Having that checkbox disabled would produce the result that you showed in the video. If that checkbox was enabled but you still did not get any tangent snap, then that woudl be some kind of bug.

- Michael

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 From:  DannyT (DANTAS)
2788.11 
This reminded me of a situation where I wanted a line tangent to a circle at a particular angle.
The work around was to draw the line tangent to the circle at 90° then rotate it at the angle needed.

Anyone with an easier way, maybe I'm missing something.

---------
~Danny~
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 From:  Michael Gibson
2788.12 In reply to 2788.11 
Hi Danny, well just doing a rotation transform on the line after you draw it is a pretty straightforward way to get that.

But I guess a quicker way would be to create a construction line, and then use the option for rotating the construction line. For example here I draw a line angled at 45 degrees from the circle tangent at a point, using this method:



To get the pop up menu with the various cline options, press and keep the mouse button down on that little launcher tag for about a second.

- Michael
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 From:  DannyT (DANTAS)
2788.13 In reply to 2788.12 
Hi Michael,

> well just doing a rotation transform
> on the line after you draw it is a pretty
> straightforward way to get that.

Yeah, that's why I didn't mention it before it was no big deal to do, but because of this thread it reminded me of the situation, so I thought maybe you could have a look at it.

What I was getting at was more like this situation.


---------
~Danny~
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 From:  Michael Gibson
2788.14 In reply to 2788.13 
Hi Danny, I think I see what you mean, you want to find the point on a circle that will give you a tangent line of that angle.

Before when you were talking about rotation, I had thought you meant rotating the line around one of its own ends, but I think I see that you meant rotating the line around the center point of the circle?

You can actually still use an angled cline to help with this if you want - if you draw in an cline at the desired angle, you can then drop a second cline using perp/perp snap to get the point you want:



That's sort of like using the cline as a temporary angled grid.


But another method that may be easier for you is to set up a construction plane angled by 30 degrees, which will then give you a quad snap at the point you want.

When setting this cplane, you may want to uncheck the "Orient ortho views" option so that your top view will stay the same and you will see the angled cplane. To do that, click a point for the cplane origin, then type <30, and drag the x axis to angle it at 30 degrees. Then use quad snap:



It looks like there is currently a bug where setting angle constraint does not work properly if you try to adjust the cplane from its current location instead of picking a new origin point for it, so until I fix that in the next beta you need to pick an origin point anywhere for the angle adjustment to work in the cplane tool.

- Michael

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 From:  BurrMan
2788.15 In reply to 2788.14 
Would this work in other situations?


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 From:  Michael Gibson
2788.16 In reply to 2788.15 
Hi Burr, that's a cool one, I think that does work because you basically form this isosceles triangle here:



which has the same angles as the extended one:



But sometimes it can be hard to remember a method that involves drawing things in a kind of different initial direction than what the main goal is though.

- Michael

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 From:  Michael Gibson
2788.17 In reply to 2788.15 
Hi Burr - for speed, I would think that your method there is going to be the fastest since you get the right snap point after creating just 1 construction line.

Not much room to get much faster than that...

- Michael
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 From:  DannyT (DANTAS)
2788.18 
Thanks Michael and Burr !

From what you guys showed there I ended up refining it a little further :)

Type the angle, one construction line.



Cheers
~Danny~

EDITED: 20 Jul 2009 by DANTAS

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 From:  BurrMan
2788.19 In reply to 2788.17 
Just to be clear, if I was going to do any kind of isoscele, I would have to go out to the backyard and dig that guy up and take his bones far, far away! :O
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