I was just at the Square 1 sketching conference and Jeff Smith gave a workshop about going from CAD to sketching and I really liked his approach. He didn’t talk about what happened before this step but I can imagine it goes like this : Sketch thumbnails/ideation sketches, narrow down your concepts, quickly model a rough underlay in cad, throw an environment around it and then save and use as your underlay. This provides not only your underlay, but all of your light and shadow is figured out for you accurately. And you can very quickly change the views of the model so you can output 10 underlays in the amount of time it may have taken you to output 1 or 2 with sketching. Everyone has different speeds though and this approach is new to me so I’m still experimenting with it, not sure if it will stick or not, there is something I love about using a grey marker for creating underlays