QUOTE(johannes @ Oct 8 2010, 08:19 AM)
Your method with the squares is way to complicated. Usualy, you decompose the shape in basic geometry like rectangles, triangles, disc and you can approach the surface very quikly.
Sorry, yes, I assumed whoever would do this would realize that you do not need to count every granular grid square individually (1, 2, 3...). Large areas can be resolved quickly by converting into shapes. As you say, boxes, triangles and portions of circles alone would get you pretty close. Clearly its the area around the edges that require more attention and how close your shapes matches defines your accuracy.
And clearly you have shown a cheap way to do this via computer. This assumes your image you are starting with is accurate. I have seen that image before and I assume it is sourced from a Porsche document of some sort. The question is if that is an accurate rendering, or an artists rendering that just happens to look right. If I was taking the time to do this, I would create an accurate image via photo just to be sure. That also lets you handle different car configurations (GT flares, wider tires, different air dams, etc.)
It should be relatively trivial to create an outline of the car via a photo. I have used Sketchup very little, so I can't say if it will, but I have used other tools to create vector diagrams by tracing an outline of a photo which could then be imported into Sketchup.