What would be the best way to create a symmetrical pattern in Gimp(or something free)? I am thinking of things like Compasses, etc. Is there an easy way, or is it just one of those things that you have to just be careful doing? Eg.

Say I want to create an arrow:
___________
\__________\
/__________/

Hopefuly, my poor ASCII art skills get across what I am trying to accomplish here, ie, a tapered head and tail with a bisecting center line.

Likewise, how would someone go about making a slightly more complicated pattern such as a Celtic knot or or something like that? Are there any free tools out there that help do this sort of thing?