constructing a round using a circle with two tangential points

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Krischu
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constructing a round using a circle with two tangential points

Post by Krischu » Tue Sep 17, 2019 9:46 am

Bildschirmfoto 2019-09-17 um 10.44.08.png
Bildschirmfoto 2019-09-17 um 10.44.08.png (180.35 KiB) Viewed 481 times
How would I construct the small left circle. In this drawing it is just drawn so lá lá, not precisely constructed

One point is the endpoint of the line. The other two points are the tangent points of the two lines against the circle.
(N.B. the radius isn't known beforehand and the tangent points aren't either as well).
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Re: constructing a round using a circle with two tangential points

Post by TSG » Tue Sep 17, 2019 11:31 am

Thomas
Last edited by TSG on Tue Sep 17, 2019 11:39 am, edited 1 time in total.

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Re: constructing a round using a circle with two tangential points

Post by CVH » Tue Sep 17, 2019 11:33 am

You could draw a vertical construction line at the endpoint and use 3 tangent.
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Re: constructing a round using a circle with two tangential points

Post by andrew » Tue Sep 17, 2019 12:39 pm

Draw > Circle > 2 Tangents and Point:
https://qcad.org/doc/qcad/latest/refere ... /Circle2TP

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Re: constructing a round using a circle with two tangential points

Post by Krischu » Tue Sep 17, 2019 1:06 pm

andrew wrote:
Tue Sep 17, 2019 12:39 pm
Draw > Circle > 2 Tangents and Point:
https://qcad.org/doc/qcad/latest/refere ... /Circle2TP
This doesn't seem to work. I'm asked for first line or circle, second line or circle and when being asked for "point on circle line" it doesn't snap at the endpoint.

@CVH: 3 Tangent works.

Thanks
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Re: constructing a round using a circle with two tangential points

Post by Krischu » Tue Sep 17, 2019 1:06 pm

TSG wrote:
Tue Sep 17, 2019 11:31 am
Thomas
What were you going to tell me? :)
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Re: constructing a round using a circle with two tangential points

Post by Husky » Tue Sep 17, 2019 8:08 pm

Krischu wrote:
Tue Sep 17, 2019 1:06 pm
This doesn't seem to work. I'm asked for first line or circle, second line or circle and when being asked for "point on circle line" it doesn't snap at the endpoint.
The CT2 tool is built to solve the task easily without auxiliary lines.

Try this click order:

Husky-2019.09.17-02.png
Husky-2019.09.17-02.png (40.3 KiB) Viewed 447 times
If it still not snap to the endpoint doublecheck your Auto Snap settings. End Points should be checked:

Husky-2019.09.17-03.png
Husky-2019.09.17-03.png (22.58 KiB) Viewed 447 times
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Re: constructing a round using a circle with two tangential points

Post by CVH » Tue Sep 17, 2019 10:11 pm

Husky wrote:
Tue Sep 17, 2019 8:08 pm
Krischu wrote:
Tue Sep 17, 2019 1:06 pm
This doesn't seem to work. I'm asked for first line or circle, second line or circle and when being asked for "point on circle line" it doesn't snap at the endpoint.
The CT2 tool is built to solve the task easily without auxiliary lines.
Try this click order:
Sorry, but when your point is at the bissectrice there is no solution....
And that should be the easiest one, one only!
Last edited by CVH on Mon Sep 30, 2019 8:46 am, edited 2 times in total.
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Re: constructing a round using a circle with two tangential points

Post by TSG » Tue Sep 17, 2019 10:17 pm

I agree. In this case with QCAD 3.23.0.0 and macOS Mojave the tool ct2 doesn't work.
When snapping to the endpoint or any other point on the line all solutions disappear.
I think it's a bug.

Thomas

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Re: constructing a round using a circle with two tangential points

Post by Husky » Tue Sep 17, 2019 11:36 pm

Interesting! :shock:

Guys - please do me a favor: After you mentioned it doesn't works (and it was flawless working for me!) I tested a bit and discovert something interesting. I won't tell you now the result ....

This dxf has two identical situation. Please test on each on them what I posted as solution for this task and tell me how it works for you. Thanks.

CT2.dxf
(110.61 KiB) Downloaded 32 times
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Re: constructing a round using a circle with two tangential points

Post by TSG » Wed Sep 18, 2019 9:06 am

e_surprised e_surprised e_surprised

#1 doesn't still work (no solution)
#2 works as expected (found 2 solutions)

Couldn't found any difference between the situations.
What's the reason for that?

Thomas

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Re: constructing a round using a circle with two tangential points

Post by Krischu » Wed Sep 18, 2019 9:30 am

macOS mojave 10.14.6
Qcad 3.23.0.0


Invoking ct2 on example 1. results in the solution circles disappearing when selecting the endpoint (3.)
Bildschirmfoto 2019-09-18 um 09.22.41.png
Bildschirmfoto 2019-09-18 um 09.22.41.png (18.27 KiB) Viewed 395 times
Doing the same on example 2. results in showing the two circles for choice end lets choose the desired solution circle:
Bildschirmfoto 2019-09-18 um 09.21.39.png
Bildschirmfoto 2019-09-18 um 09.21.39.png (22.47 KiB) Viewed 395 times
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Re: constructing a round using a circle with two tangential points

Post by TSG » Wed Sep 18, 2019 9:35 am

It's getting warmer...

When moving #1 down CT2 works.

Thomas

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Re: constructing a round using a circle with two tangential points

Post by Husky » Wed Sep 18, 2019 9:51 am

Thanks for testing!
TSG wrote:
Wed Sep 18, 2019 9:06 am
Couldn't found any difference between the situations.
Both situation are exactly the same (copy). Difference is only the location. e_surprised

CT2 behaves differently simply based on where it is used. Thomas, you expected already a bug - will you file a bug report?
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Re: constructing a round using a circle with two tangential points

Post by CVH » Wed Sep 18, 2019 10:00 am

Flaw depends on order reference line selection and selection place.
Flaw never 1 unique on bissectrice.
Flaw regions 0 instead of 2, 1 instead of 2 (drew quick and dirty).
Regions not strickt. Very tiny diffs may comply or not.

Regards,
CVH
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