The separately rendered layers were assembled in compositing. This allowed us to manipulate each element on its own, by adjusting colors, adding fog, depth blur and so on. Object shadows cast on the ground were rendered into the alpha channel of these layers, so they were automatically 'added' into the composite.
To better integrate objects and characters into the shot, a few little tricks were applied in compositing. A matte was generated from the alpha channel's edges, and it was used to blur the layer a little bit, making the shiluette edges fuzzier. Large objects like vehicles had a soft contact shadow to simulate global illumination; this was usually painted in a texture and rendered as a plane under the object, then used as a matte for brightness adjustment on the ground plane layer.
Smoke and dust elements were rendered as transparent polygon particles, using the Maya hardware renderer. The resulting greyscale image was again used as a matte in compositing, where the colors could be adjusted interactively.
All in all, we're happy with how the project turned out in the end. We've learned a lot during the production, and I hope that we can help you in creating your cinematics by sharing our experiences.
More images from Afrika Korps