Problem. You want to capture all those lovely high rise buildings in your city of your choice.

You know you need to take into account the parallax error (because the satellite photography is rarely straight down), but you can only see the roof of the building, not its position on the ground. What to do?

Well it may be obvious to some but I only worked it out today. Trace the top of the building anyway, and at the end just use Potlatch to slide the shape into place on the ground.

So much easier than estimating the offset in your head and kinda drawing with a tilt!