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Circle - Tan Tan Radius: Tangent drawn on wrong side?

sascari
Advocate

Circle - Tan Tan Radius: Tangent drawn on wrong side?

sascari
Advocate
Advocate

How does circ-tan-tan-rad decide which side of polylines to draw? Sometimes it's on one side and sometimes it's on another side. Does it matter if dealing with arcs or circles? 

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tramber
Advisor
Advisor

@sascari wrote:

How does circ-tan-tan-rad decide which side of polylines to draw? Sometimes it's on one side and sometimes it's on another side. Does it matter if dealing with arcs or circles? 


The result is depending on where you specified the tangeancies, that is for sure.

What I mean is clicking on an object is also clicking about where you wish to be tangeant.

This is why the result can be on a different side if the objects implied are circles or arcs

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sascari
Advocate
Advocate

Ok. I think what you're saying is Autocad looks at where exactly you click on the object to specify the tangencies and takes the radius input to determine which side to draw it on. I didn't know it takes into account the location of the tangencies (I assumed it estimated a best fit scenario). That kinda makes sense... Is there an easier way draw a best fit arc tan tan rad that limited to whole integers? 

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imadHabash
Mentor
Mentor

Hi,

 

>> How does circ-tan-tan-rad decide which side of polylines to draw? <<

as i understand ... tan-tan-rad is used to draw a circle using another existing circles and you said polylines ... maybe with more details it will be more clear.

 

>> Does it matter if dealing with arcs or circles?  <<

two different commands with special uses . what is your case to give you a direct answer.

 

Regards,

Imad Habash

EESignature

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sascari
Advocate
Advocate

hi amadHabash. Thanks for the reply. I should have specified arcs only. What is the other command? 

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imadHabash
Mentor
Mentor

excuse me ... when i wrote "two commands " i mean that using circles and arcs. till this moment i have not catch your issue .

 

Regards,

Imad Habash

EESignature

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tramber
Advisor
Advisor

Look :

if you want to draw a bicycle chain between 2 circles.

You gonna ask for a line, staight on, you gonna ask for a TAN obj snap, just before a first click.

Then you gonna click on a side of the circle 1 and ask (again, by a CTRL+right-click, for instance) another TANgeant snaping on the right side of the circle 2.

 

You see !?

It is what we call a Temporary objectsnaping.

 

Perpendicular is another exemple of a temporariable snaping !

 

It helps to understand this very particular application you are asking about in the Circle Command.

 

You can do all those things on so many kind of objects, that it is not a discusssion.

 

PS : I know many people who pretend they know Acad perfectly who never knew more than 50 % of object snaping real functionnality...

Temporariing may be fantastic and depends on where to apply, ... before to apply !

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sascari
Advocate
Advocate

Ok. Here is an image to help illustrate the issue. Sometimes when I draw tan-tan-rad the circle lands on the left and (A) and sometimes it lands on the right (B) of the two components that it is trying to be tangent to. I'm unclear as to what drives this action.

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tramber
Advisor
Advisor

If, mathematicaly, the soft finds only one solution, it will give it.

If it finds several circles, then it tries to do its best choice according to where you did your actions, that is what I think.

 

You have to be frank in you gesture, but, can you pretend to know easily where your click should be ? I don't think so. I myself do the thing several times before obtaining what I want.

It is mathematical*, Acad is always in the truth.

 

With 2 lines, your question is not to be. With circles, it is almost philosophical* !

 

*historicaly, they are the same

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sascari
Advocate
Advocate

Yea, I see your point. It would be helpful to know how it is determining the inside/outside for the tangents so as to speed up the process. Thanks for your help with this. 

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tramber
Advisor
Advisor

Make tests, it's fun !

Start with our famous Ttr Circle on 2 perpendicular lines that crosse. It will always depend on the 2nd click

The same between 2 circles.

So, beware of the 2nd click

When you draw a bicyle chain, beware of the 2 clicks and not only the 2nd !

 

To conclude : everything depends !

 

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leeminardi
Mentor
Mentor

Depending on the size of the two circles, their location, and the radius of the circle to be added, there are up to 8 possible different locations that a TTR circle can be places.  This image below shows eight circles of the same radius tangent to the two white circles.

 

ttr.JPG

Which circle you get of these eight possibilities depends on where you give the tangent location picks.  The the circle ttr command will choose the circle that has its tangency closest to the points you specify.

 

lee.minardi
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