He came out the first time to talk about the project and work out the scope and get an idea of my backyard. That took like an hour. The only notes he took were on the pole sizes, eyebolts, brackets etc...
When they came out to dig and pour the piers, I had marked the location with stakes based on some math I did on graph paper. The locations were really determined by my deck shape. They took about 3 hours to dig, form and pour the piers. They came 5 days later to install the posts and paint them.
Initially I had 2 20x20x20 equilateral triangles, but I could not get the second one positioned over the pool with equal tension. I put the locations into CAD and played with shapes and figured a 20x20x28.5 right triangle would fit.
We have been in the house for years and I know the path of the sun is in direct line with my pool in the summer and the most annoying sun coming at 4pm so I had to have one sail positioned as west as I could get it.
It is a balancing of post locations, sail sizes and shapes and sun path. I think I got lucky