# tangent point between two circle problem

2 ビュー (過去 30 日間)
Yu Li 2019 年 1 月 27 日

Hi:
I have two circle that does not intersect with each other, the radius and center coordinates are known. there should have four tangent lines (two inner and two outer) and are cooresponding to four pair of tangent points.
I need the four pair of tangent points.
is there anyway to do it in Matlab?
Thanks!
Yu
##### 3 件のコメント1 件の古いコメントを表示1 件の古いコメントを非表示
Jan 2019 年 1 月 29 日
@Yu Li: You have asked a valid question concerning Matlab. You got an answer, which might be useful for other also, when they search for the same keywords. So there is no reason to remove the question. If you consider your problem as solved, you can use the "Accept" button to inform the readers, that this question does not need further asnwers.
David Goodmanson 2019 年 1 月 29 日

Hi YL,
I went a bit over the top on my original comment, which was not necessary. Since you appear to have deleted the comment I was responding to, I am deleting mine as well.
I agree with Jan that there is no need to remove the question since Jan's answer has useful information.

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### 採用された回答

Jan 2019 年 1 月 28 日

It is recommended to search in the net or especially in this forum before posting a new question. What about this solution: https://www.mathworks.com/matlabcentral/answers/162912-tangent-to-two-circles
This thread contains the suggestion to solve the easy mathematical problem at first, because the implementation is not hard: https://www.mathworks.com/matlabcentral/answers/419870-how-to-find-the-center-of-a-circle-given-two-tangent-lines-and-radius-using-matlab
The mathematical solution contains the step to create the tangents between the center of the smaller circle to two circles with the same center as the larger one, but with the radii R_large +/- R_small. Now the wanted points are obtained by a parallel movement. See e.g. http://mathworld.wolfram.com/Circle-CircleTangents.html
You are right: maybe such a function has been published in the File Exchange already. Then it is recommended to search by your own at first, and if this is not successful, to mention "I've searched in the FEX with these terms already: ..."
See: FEX: Common external tangents (I've mentioned how to expand this for the inner tangents: Replace r2-r1 by r2+r1)

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