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One of the strategies I employ when using the Pen Tool in Illustrator to trace something is to use as few nodes as possible to make the curves as smooth as possible. I'm often surprised by what curve variations can be managed between a mere two nodes, and on the other hand occasional come across seemingly simply curve segments that require three or more nodes to trace properly. As a somewhat scientifically minded person, I find myself wanting to "know" just what's going on...

I wondering whether any experienced tracers out there have a kind of mental checklist for when they need to drop another node, or whether anyone has a good summary of it from a maths point of view?

  • I'm having similiar problems, and I've coded a Bezier tool in OpenGL years ago :) Maybe I should revisit it. I'm working mostly in Inkscape but the problems are the same. I wonder if a similar "rule" would be to initially place an anchor point every where the curve of the line changes direction. I'll have to practice to find out. Let me know if that helps. – Rick Henderson Nov 14 '16 at 20:56
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Like you I wanted to know how to perform tracing best. Initially it was because I failed in tracing in MS Paint many years ago. I studied bezzier curves and from this point I should say you cannot solve every curve by logic, instead you will get some "inner feeling" where to place an anchor point. Most frequently I don't place an anchor on heels, but place in concave part of a curve, because the smooth heel created by dragging directional points of the near anchor points. Secondly, I decided to work the fastest way, thus for me the issue of clear path is more theoretical then practical one. I don't believe someone should be obsessive by removing unnecessary anchor points, because on modern pc there is sufficient memory to work and save information about millions of anchor point without affecting productivity in any way.

  • Thanks. Yeah I'm realising it's one of those things the brain just figures out after a while, but its interesting to watch the process. FYI, the reason I strive for fewer anchor points is because it makes for smoother curves IMO with less work, not because of CPU. – Hari Karam Singh Feb 25 '14 at 14:11
  • So, smoother curves you will get if you create a hill by dragging directional handles. – Ilan Feb 28 '14 at 11:56
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I've just been reading good blog post that touches on this: http://philippaberrysmith.wordpress.com/2011/08/23/advanced-pen-tool-illustrator/

It's worth a read but here are a couple highlights:

  • Work in one direction (i.e clockwise OR anti-clockwise) don’t change directions mid-drawing.
  • Keep the handles of your curves pointing in the direction you are drawing. If they point backwards, you will get nasty (or perhaps useful) bumps and squiggles.
  • It is usually best to use a semi-transparent colour to trace with, rather than a line. The thickness of the line can obscure the actual path.
  • Aim to create as few points as necessary.
  • Make extrema points to start with. They are a good place to start, before you get a feel for where the “next point” should go. Extrema points are those points situated on the horizontal or vertical flatness of a curve. Use the Shift key to ensure accurate 90° lines.

To this I'll add...

  • You can make two points do a lot more bending then you might think. Try covering huge sections with just two points and see how much you can get away with (key shortcut: when mid-trace with the pen, hold down the space bar to relocate the last point you created)
  • But, there are definitely certain kinds of bends, even on short segments, that can't be covered by two points alone.

I still struggle to understand the logic enough to put it into words, but from what I gather, it's not a perfect science and you get a feel for it after a while. I suspect Bezier maths is no walk in the park hence the inability to state it's limitations plainly.

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