There are lots of software options to do that sort of thing, but I find Photoshop to be the easiest for me. Not sure if you are familiar with it, but I just use the shape tool to draw a rough ellipse, and then use the Transform command (CTRL + T) to stretch it and move it around to match the bow. It only takes a few seconds to do.
I also bought a copy of Adobe Lightroom, since I have recently become a DSLR photography enthusiast. I just learned the other day that I can shoot video with my camera while exercising the bow, import it into Lightroom, and then export any single frame from the video as a picture that I can later edit (there is probably free software out there that will do the same thing). Needless to say, this comes in handy when trying to capture a full draw picture, as I don't have to hold the bow while I wait for the camera to do it's thing. Watching the video back on repeat helps me judge the tiller as well, since I can really focus on the bow, instead of worrying about the draw length and weight that I am pulling the rope to. When I make bows, I have all the time in the world. Some people will scoff at the idea of what I do, but if I figure that if spending a little of my downtime analysing pictures can help make the difference between a good bow, and great bow, then it's time well spent.
The shape you see has nothing to do with the intended final tiller - at this point I am using it strictly for judging if there are any stiff spots, as well as symmetry, as you mentioned. Some people can do this strictly by eye. Although I do trust my eye, sometimes it's nice to have a second opinion
In the case of this bow, I hope to leave the handle area just slightly stiffer than a full-compass tiller, just to reduce the handshock a bit. So to compare it to a circle would not quite be what I am after. As the tiller progresses, you will see the shape come closer to circular, but it won't quite get there (hopefully! I will likely have to leave that area alone now for the rest of the tillering process).
Now, a question for the warbow gurus on here - I probably won't get to work on the bow much until the weekend. Looking at that last snapshot, I'm thinking that I should be working around the area about 2/3rds of the way out from the handle, and leave the very tips until they start coming around more? Then when it comes time to soften up the tips more, I will probably try to tiller them a bit from the side again to hopefully help bring the string back over the handle as much as possible.
Am I on the right track?Mark, when I get back to tillering I will try your suggestion and give the limbs a gentle nudge in the right direction. How far would you suggest pulling the string back, 10 inches or so?
Thanks everyone for all of the feedback so far. As much as I normally like to have projects planned out before even starting them, I am definitely learning some things on-the-fly, and it's nice to have some experienced eyes watching over me on my first "heavy" self bow.