Marvelous Shade. It definitely serves the purpose for which it was intended: there is shade for grandson and for our living room.
There have, however, been some problems. The middle sags and the canvas stretches.
After I had set my posts, I discovered Shade Sail Installations. In this they suggest two high and two low connections.
When I build something, I usually have to rebuild a lot. I don't do enough research. I just jump in with both feet and create. So after the fact, I did try to make the "hypar" design. I took down 3 of the corners and then moved the eye bolt across from the high post as far away as possible. That stretched the canvas on the bias. Then I attached the other 2 corners. I could not change the heights, but it did help some.
You must also have some way to tighten the connection after it stretches. If you have some help, you can pull the canvas and then tighten the covered cable connectors. I have also added a turnbuckle to every corner.
Let me know if you figure out a better way to keep tightening the canvas.