@Rich-O-Brien Sometimes SketchUp was crashing, sometimes SU Podium crashed, and sometimes windows crashed. Shop sorted the problem by changing the motherboard, they said that there was an incompatibility that they couldn't find. Since I've had it back it's had PodiumxRT go down once, but ShetchUp stayed running.

OK. That's helpful and thanks for updating your profile. So in order to prove that the shadows are a reasonable representation of reality, perhaps you could geolocate a sample model at the offices of the government agency and show the shadows for the current date at a specific time. Maybe use a flag pole on the site so they can compare the image to what they see when they go out there and look at it. Reminds me of a project I did for a client in Maine some years ago. I'm in Minnesota and at the time I was working on the project I'd never seen the site. The city folks wanted proof the dimensions I was giving them from the site were accurate. I created a simple drawing of their municipal building (which I had also never seen in person) and told them how long and deep it was. That convinced them and my client prevailed over a contractor who was providing extremely inaccurate pencil sketches.

It also sounds like you've assigned tags to geometry (edges and faces) which is not good practice. Only objects (components, groups, labels, and dimensions) should get tags. Edges and faces should be created AND remain untagged.

I can't tell you why it works well, but I've been really happy with this one: nvidia geforce 9400gt, 1gb ddr2, pci-e 2.0