Drawing a line segment (or an arc) with an arrow head placed somewhere between the endpoints

Question

I am trying to draw a line (or an arc) in Adobe Illustrator that looks something like this:

(Picture taken from Allen Hatcher's ``Notes on Introductory Point-Set Topology,'' pp. 22.)

My problem is that I can't place the arrowhead exactly halfway on the curve between the endpoints, or on any point on the curve.

Can anyone please help me?

Answer 1

One simple way to add an arrowhead halfway along the path would be to split the path into two segments, and add the arrowhead to the first half.

1. Draw the path, in the normal fashion. In the example you gave, I'd use the pen tool and draw a bezier curve with a starting point at “x” and an end point at “z”.

2. Split the path. If it consists of only a start and end point, selecting Object > Path > Add Anchor Points will add a point centred along the path. Then choose the scissors tool (shortcut C) and click on the newly created path point, to split into two paths.

3. Add the arrowhead to the first half of the path. Note that arrowheads can either extend past or remain within the length of the path. In this instance choose extend past, by opening the Stroke panel, choosing “Show options” from the panel's fly-out menu, and selecting the correct 'Align' option.

Answer 2

Step1: Create 4 circles

Step 2: remove unwanted arcs (joining strokes is not necessary, but optional if you want to play around with anchors)

Step 3: Copy top 2 arcs into new layer (when pasting, use cnrl+shift+alt+v to paste in exacly same place) and add arrow ends

Step 4: Show both layers (note - otherwise, have undesirable stroke endings meeting arrowheads)

Step 5: Add circles & letters

Note: If for math publication, you might want to create using TEX as opposed to Illustrator (there is a good Tex SE) for more professional finish/ proper mathematical fonts, etc

Answer 3

As a alternate to slicing the path there is a script that can help you. Its called distribute on paths.

• distribute on path, by Hiroyki Sato.
• also useful if you want more arrows is dupAlongPath, also by Sato.

This script takes any number of objects and spreads them along a path nstead of a direction. The script has a alternate option to rotate the object to align to the path. If you distrbute one object t should be smack in the moddle of your path like you ask.