## Creating a circle to pass through 2 points

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matt____jackson
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Joined: Wed Jul 03, 2019 11:34 am

### Creating a circle to pass through 2 points

In simple terms, I have a rectangle that is 152cm long x 18cm tall. I want to draw a circle that passes through the top right corner and the bottom left corner to create a 'slope'. (I then plan to delete the top and left hand lines of the rectangle so that I am left with essentially a triangle that has 2 straight sides and 1 sloped side).

In the attached picture I have drawn a circle manually, is there a way to pick the 2 points of the rectangle so that it's precise?
Attachments
Screenshot 2019-07-11 at 4.37.04 pm.png (241.94 KiB) Viewed 2710 times
QCAD-Pro v3.22.1 on MacOS.

andrew
Posts: 6548
Joined: Fri Mar 30, 2007 6:07 am

### Re: Creating a circle to pass through 2 points

A circle is not defined from two points on the circle lines.

You need more constraints, for example:
Circle from three points
Circle from two points and a radius
or
Circle from Tangent and 2 Points if the circle is a tangent to the top line of the rectangle.

matt____jackson
Active Member
Posts: 25
Joined: Wed Jul 03, 2019 11:34 am

### Re: Creating a circle to pass through 2 points

andrew wrote:
Thu Jul 11, 2019 4:58 pm
A circle is not defined from two points on the circle lines.

You need more constraints, for example:
Circle from three points
Circle from two points and a radius
or
Circle from Tangent and 2 Points if the circle is a tangent to the top line of the rectangle.
Ah right, ok. Any suggestions how I can work that out? I need to draw a slope that drops by 18cm over a distance of 152cm but I don’t know the radius of the full circle.
QCAD-Pro v3.22.1 on MacOS.

andrew
Posts: 6548
Joined: Fri Mar 30, 2007 6:07 am

### Re: Creating a circle to pass through 2 points

There are an infinite number of circles that satisfy that criteria. Your circle is quite simply not defined. It's impossible to drawing something accurately if you don't quite know what you want to draw... So that's the problem you'll have to solve first: what do you actually want?
Screen Shot 2019-07-11 at 18.36.36.png (37.44 KiB) Viewed 2696 times

Husky
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Location: USA

### Re: Creating a circle to pass through 2 points

matt____jackson wrote:
Thu Jul 11, 2019 6:30 pm
Ah right, ok. Any suggestions how I can work that out? I need to draw a slope that drops by 18cm over a distance of 152cm but I don’t know the radius of the full circle.
As Andrew already said ................... without the proper information it is just a guessing game.

One solution what I can think of is to reduce the guessing with a horizontal help line (yellow) which has to snap to the end of the vertical line. Then draw a 3 point arc, First point snap to the left end of the horizontal line, second point guess the best position, third point snap to the end of the vertical line.

Husky-2019.07.11-01.png (9.04 KiB) Viewed 2694 times

If that doesn't comes close enough to that what you are looking for you can manipulate the radius with dragging it (1, blue point) to the right position.

Husky-2019.07.11-02.png (8.15 KiB) Viewed 2694 times
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matt____jackson
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Posts: 25
Joined: Wed Jul 03, 2019 11:34 am

### Re: Creating a circle to pass through 2 points

Ah, I realise I’ve missed out a potentially important bit of info then: where the circle passes through the top right hand corner, that exact point wants to be the very peak/highest point of the circle.

Secondly, where the circle passes through the bottom left corner, it must be before the widest point of the circle.

Does that help define it further?

Please excuse my ignorance with all this, complete newbie.
QCAD-Pro v3.22.1 on MacOS.

andrew
Posts: 6548
Joined: Fri Mar 30, 2007 6:07 am

### Re: Creating a circle to pass through 2 points

In this case, you're looking at Circle from Tangent and 2 Points:
1. Click the top line
2. Click the top right corner
3. Click the bottom left corner

matt____jackson
Active Member
Posts: 25
Joined: Wed Jul 03, 2019 11:34 am

### Re: Creating a circle to pass through 2 points

andrew wrote:
Thu Jul 11, 2019 7:58 pm
In this case, you're looking at Circle from Tangent and 2 Points:
1. Click the top line
2. Click the top right corner
3. Click the bottom left corner
Magic!!!! Thank you. I don’t know how I can show appreciation for the help but that’s brilliant!!!
QCAD-Pro v3.22.1 on MacOS.

Arie Kabaalstra
Newbie Member
Posts: 5
Joined: Sat Dec 24, 2011 11:51 am

### Re: Creating a circle to pass through 2 points

If you want to run the circle Tangent to the top of the rectangle just use Circle "Tangent and 2 points,
First click the top line of the rectangle, and then click the two corners the circle has to run through.
That way you get the circle not sticking out of the rectangle at the top.. if i understand correctly, that is after all what you aim to achieve.

(edit.. Oops.. someone already mentioned that)