Making a circle to intersect with other path(s) in Illustrator

Question

I want to do this

But when I zoomed in I got this

This is problematic because I need to cutout some of intersecting are using shape builder tool. Some intersection is not cut while other leaks.

I am going to intersect tons of circles because I am making a golden ration(ed) logo, instead of tracing it down. If I don't fix this kinds of thing ASAP I get this

Now I had to redo everything after I am waiting for answer.

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BTW I KNOW THIS

Disable Allign to Pixel Grid from Transform Menu

And CTRL + DRAG TO ALLIGN THE CIRCLE

Apparently, this do not work too. If I zoom in deeper it is still misaligned.

WHAT I WANT IS MAKING A CIRCLE WITH THE CENTER (A) and INTERSECT POINT (B) [CTRL+CLICK at A DRAG to B and have it intersect B automatically] without adjusting it afterwards because I will then have to move the center (A) slightly to the left which I something I do not want.

Answer 1

There is a trick to accurate circles

If you want accurate circles, then do not draw them with by dragging the ellipse tool. It is not a circle tool (you can get one here). Using ellipse tool like this would be way too inaccurate. Instead what you do is you draw a line that represents your radius. Then measure your line and alt click on the point you want the center to be at and TYPE in the radius.

Image 1: When you alt click you get a dialog to type the accurate radius you measured with the line tool

This is way more accurate, and it is even more accurate in illustrator CC (since you can get more digits on the line)

Image 2: If you want accurate circle intersections TYPE the radius from meaurement

If you want to find intersections between other things, same thing applies except that you need to use smart guides on your circle.

Since this can get boring to do over time Ive written a script that will draw a circle if you draw the radius line (since i can not always install subscribe):

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);
}

Answer 2

I do not blame you for wanting this to be better. Lord knows there are times I wish Illustrator was better at this. My answer is not meant to convey a sentiment that you are incorrect in your workflow or methods in any way, but merely explain why things aren't as you want them to be in terms of snapping.

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Unfortunately paths of circles won't align to anything automatically themselves. Arcs are a difficult thing for Illustrator to align mid-path. Only the anchors along the circle's path offer any sort of real snapping. In other words, you won't get "a circle to intersect with other paths automatically". You can only get the anchors along a circle to snap or other paths to snap to the circle.

You can turn on Smart Guides (View > SmartGuides) and that will offer some snapping to the circle paths when drawing other paths. So, drawing a path you want as an intersect with the arc of a circle will snap the arc with Smart Guides enabled.

In addition to disabling Align to Pixel Grid, you may or may not want to enable/disable Snap to Point (View > Snap to Point) as well. If your circle arc happens to not be crossing an exact point, and Snap to Point in enabled, then your end anchor may not rest along the circle precisely. With Snap to Point disabled and Smart Guides on, you should be able to draw a path and have it snap to the arc of the circle.

The issue here...

.. is you are expecting Illustrator to align an anchor on the intersection of two arcs. Illustrator doesn't calculate that intersection. It calculates the arcs individually from their anchors, so it can snap to each arc, but illustrator doesn't see that intersection as a snap point. You have to manually ensure things align in such instances.

In short....

• Snap Paths to circle arc = yes
  
• Snap circle arcs to paths = no
  
• Snap path to multiple circle arcs = no

On the whole, Illustrator isn't always a precision tool like a CAD application would be. It's a drawing tool first, precision if kind of an afterthought in many areas. While it attempts to be precise, there are times when you need to use other features such as View > Outline or Object > Path > Average to get anchors to precisely line up. Depending on your goal, it is often necessary to take that extra step to align things. I don't fully understand the apparent issue with that. Precision takes a bit of extra work, as it does in any application.

If the goals is absolute precision, I'd suggest you work in Outline mode entirely for the set up. The strokes on paths can easily cause you the think something is aligned when it isn't whereas in Outline mode, you just see the actual paths.