Illustrator: Using 'Unite' Function in Pathfinder Window Creates Erroneous Anchor Points/Shifts Shapes

Question

I have two shapes, in this case red and dark blue circles (for clarity), that I want smoothly connected by a tangent line and eventually united into a single, monocolor shape path.

I am using the 'Tangent Line Tool' from the Astute Graphics SubScribe v2 plugin to create my tangent line between my two shapes (I've also tried this manually and using another free Common Tangents plugin, and I run into the same issue.)

So, I create my tangent line (green with thick stroke for illustrative purposes) between the red circle and dark blue circle. I've highlighted the endpoints of the line in light blue. So far so good, outline looks pretty precise to the naked eye and is the tangent I want.

In order to unite the shapes using the pathfinder, I'll need to turn the tangent line into a shape, it can't just be a line, so I do that. Leaving the original endpoints of the tangent line exactly where they were, I connect the end points of the tangent line by making two new points, thereby creating an arbitrary square shape with the Pen Tool.

I zoom in as much as I can on the tangent line point that overlaps with the red circle; so far all the points are where I left them and look OK.

Now here's where my problem arises. I hit Unite in the pathfinder to join the red circle with my green square, expecting Illustrator to make a nice clean monocolored shape leaving my points exactly where they were, then BAM, the shapes unite but Illustrator has for some reason shifted the shapes before uniting/created two points and nudged them away from the original point position, dirtying up my nice clean shape path. See the issue highlighted below in light blue circle.

Using the Shape Builder Tool also results in the same problem.

Snap to grid, snap to pixel grid, snap to point, etc. are all off, and it doesn't seem to matter whether I'm working in a web or print doc, or in pixels, points, or otherwise.

I know I could just fill in the tangent shape the same color as the entire shape I'm making and leave things overlapping, but I won't have a nice single, clean shape path.

Is there any way to get around this? Any insight is highly appreciated.

Answer 1

Either your rectangle is faulty or your Illustrator version makes errors. Here's my attempt. I use legacy stuff.

In the left there's a circle as Illustrator draws it with the ellipse tool. It has got no transforms after it was drawn.

The rectangle is drawn with the rectangle tool and rotated around the center of the circle. Inside the red circle the joint should be tangential and it looks tangential in the outline view mode with the biggest zoom.

In the right the rectangle and the circle are united with pathfiner panel unite. Max zoom shows no fault in tangency.

It's possible that continuing an existing curve with the pen spoils it. Lock your old items and draw by clicking with the pen a brand new rectangle or drag the cornerpoints of an ordinary rectangle to the right places. This way the continuing with the pen error possibility is eliminated.

Answer 2

After furiously digging through hundreds of online posts, articles and queries with similar-but-not-quite-the-same issues, I still couldn't find an answer that effectively resolved this particular problem. I explored every option I could think of, and after several attempts (and a possible concussion resulting from repeatedly bashing my head against my desk), I finally landed on a one-click workaround that results in a nice clean shape that doesn't require one to perform any additional unnecessary steps like: deleting erroneous points, nudging things around, averaging the location of points, simplifying the path, starting with shapes that are already the same size/at 45° or 90° angles, or using shapes that started centered and rotated around the center of one another.

As far as I can tell, this is a problem inherent to Illustrator that surfaces whenever you are attempting to unite tangent lines between shapes that are of different size, arbitrary distance, result in lines that aren't at a 45° or 90° angle, AND/OR weren't created centered and rotated around the center of one another. If one or more of the aforementioned statements is true, no matter how dead-on these scripts/plugins are when they create the tangent lines, the result will always end in Illustrator creating a shape that gets nudged and has erroneous anchor points when you click Unite.

Now for the solution: In the scenario where you are trying to create a clean shape from tangent lines joining shapes that don't meet ALL of the requirements above, the ONLY way I've found that works is to edit a default value of Astute Graphics' SubScribe Tangent Line Tool. With the tool selected, hit Enter/Return to bring up its Preferences and check the 'Add Points to Existing Paths' checkbox. Once you've done that, you can create the tangent lines between the two existing shapes as usual. Just join the end points of the tangent lines to create a quadrilateral (using the Pen Tool or Ctrl/⌘+J, either way works fine). Now click Unite and you're golden, no erroneous points, no shifting of shapes, everything is as it should be.

Sadly, this means you can't use the free Common Tangents script for this scenario, but at least there is some way around it.