1

I have the line drawn at a random angle like this

How do I draw a circle with a center at the one end of line and with a radius of the line length.

  • Your image isn't showing, by the way. – Wildcard Jun 21 '17 at 18:17
3

Hold the alt and shift key.

Alternatively, to be even more precise you can take note of the length of your angled line. It'll say something like "D: 13.67" then click circle tool and just click anywhere on your paper and enter in twice the D of your line (since you want it to be the radius not the diameter).

  • Second method is kinda not precise: when I use pathfinder merging tools it turned out that there is no exact intersection with patches. First method does not work for me for some strange reason: dl.dropboxusercontent.com/u/585158/2017-02-17_10-52-54.gif – binariti Feb 17 '17 at 18:58
  • @binariti the first method won't hit the anchor point, you have to eye it. You can somewhat work-around this if the line is horizontal or vertical. Then it will track the anchor point but you then have to go slightly off it or you'll end up with a "flat" circle (a line). That's why I offered you the second, precise method. I don't know why you think the second method doesn't work or why you're using pathfinder merge tools? – Ryan Feb 17 '17 at 19:26
  • dl.dropboxusercontent.com/u/585158/2017-02-17_11-47-56.gif What I want is to draw a circle to it intercept with the gray figure on the right (you can see it in my gif) And when I use calculated radius the lines of shapes does not intercept in one point. What I thought about is that there should be some simple way in illustrator to draw precice circle without eyeballing and line length calculating... – binariti Feb 17 '17 at 19:52
  • Sorry there was calculation error in previous gif, but non the less this method does not give precise results. Here I've got two intersection points: dl.dropboxusercontent.com/u/585158/2017-02-17_12-08-15.gif – binariti Feb 17 '17 at 20:10
  • @binariti you do understand that bezier circles aren't exact so eve if you pluck right numbers they might not hit anyway. – joojaa Feb 17 '17 at 20:42
2

You can start by drawing the circle with the Ellipse Tool, L and then adding the radius line after with the Pen Tool, P. Utilize the default smart guides and the anchor point of the circle for precision (if you have smart guides disabled, you can edit their settings by navigating to Illustrator > Preferences > Smart Guides...):

enter image description here
^ Don't forget to hold the Shift key when dragging out the circle and connecting the center point with the anchor point

If you want the radius line to be on an angle, simply select both the line and the circle, Group (Command + G), and rotate with a free transform or the Rotate Tool, R.

  • I can not use this method if the line is already created before the circle. I've mentioned angled line because it's a simplest way to illustrate my question. When line is horizontal there is no problem at all. But when it's angled, this method does not work: dl.dropboxusercontent.com/u/585158/2017-02-17_10-52-54.gif – binariti Feb 17 '17 at 20:00
  • Can you just recreate the line or use it as a template? I'm not understanding why you're stuck building off of the one you have. Also, you're close to accomplishing what you need to do in the link you sent. Just drag the circle out a little further. – zeethreepio Feb 17 '17 at 20:02
  • Sorry that I was not very clear when I asked my question. What I want is to find a way to do this geometrically precise. If I drag the circle further then illustrator will not give me guide lines for interceptions so it will not be precise. As for recreating the line - I could do it, but I asked question because I thought that there is simpler way and I just do not know about it. – binariti Feb 17 '17 at 20:22
  • In that case, ignore the guideline that pops up in your sample gif and keep dragging, it will snap to the anchor point at the end of the radius line. If you want further precision, do it in Outline Mode, Command + Y, to ensure you're hitting the anchor point. – zeethreepio Feb 17 '17 at 20:26
1

Use your L key to get the elLipse tool out, alt-click(and hold shift & drag) into one point of the line, then drag all the way to the other end of the line to get a circle going.

1

Ok so Illustrator is a bit weird in this sense. I often use @Ryans method, Its not super accurate, but then Bezier circles aren't so accurate either.

Here are 2 other options that may be more accurate.

  1. Its possible to script this. So for example

    var sel = app.activeDocument.selection;
    for(i=0; i<sel.length;i++){
       var pts = sel[i].pathPoints;
       var radius = Math.sqrt(
              Math.pow(pts[1].anchor[0]-pts[0].anchor[0], 2)+
              Math.pow(pts[1].anchor[1]-pts[0].anchor[1], 2)
              );
    
        app.activeDocument.layers[0].pathItems.ellipse( 
          pts[0].anchor[1]+radius, pts[0].anchor[0]-radius, radius*2, radius*2
        )
    }
    

    This is not the best possible circle it would be better to rotate or make a 8 point circle for example.

  2. you can get the free circle tool form astute graphics called sub scribe, also available in hotdoor cad tools, or make your own (3 lines to change in arrow example)

0

Here's another way that's not particularly fast: you can draw a circle of arbitrary size and align it by dragging the center point to one end of the line segment. Then you can use the Rotation tool to rotate it so that one anchor of it is at the angle of your segment's other end. The smart guides snap the rotation tool for you so that you know it's right on the trajectory line, if you drag over the line. Now use the E key to do a path transform to scale the circle down or up until the anchor point of the circle snaps to the other point of the segment.

0

What about taking the ellipse tool and SHIFT+ALT dragging over the inner point of your line until it reaches the endpoint of your line?

I just did that and got your line as the radius. You can adjust the size of the circle the same way to get the circle totally on the endpoint of the line (zooming in helps).

0

For drawing a circle whose diameter will be between two arbitrary points, you can also:

  1. Make a (new) anchor point at each of the two points that will become the diameter.
  2. Select both (with the direct selection tool—press "A").
  3. Average them with Object -> Path -> Average (or just press Option-Command-J on a Mac). This will be the center of your circle.
  4. Choose the ellipse tool (press "L").
  5. Click and drag from the point you made in (3). Hold down the Option (or Alt on a Windows) and the Shift keys. Option makes it so you are drawing the ellipse starting from the center; shift constrains it so you are drawing a circle.

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