One easy way to match the HDRI with the backplates and then the sun to the HDRI is to assign that HDRI to a huge sphere in the scene. Then in the camera view you can toggle the visibility of the background while rotating the HDRI. Then you have the position and a rough rotation for the sun too.
I use the HDRI rotation and the sun position as a guideline, then I try to move them a little bit to hide ugly reflections or to get better lighting. After all the image has to look cool; it doesn't matter if it's not 100% accurate (Fig.16).
I used V-Ray physical cameras. Since my backplates were raw photos, I could match the lens, aperture, f-stop and so on, which made my life way easier. Plus, since I had more than one camera, I tweaked the cameras values rather than the lights for each render (Fig.17).
To project the shadows of the APC on the tarmac, I created a plane and assigned a VrayMtlWrapper to it. It replaced the old matte/shadow of 3ds Max. With a few simple settings it was easy to make it work (Fig.18).
Finding the right composition in all the photos was quite complex. There were plenty of things to keep in mind, which is easy in theory but very hard to achieve in practice. I'll try to make a logical and easy path to follow:
: As I finished the model, I knew which angles it looked nicer from. So all the images exposed the best angles and avoided the worst ones. Banking the camera a bit gave a tougher and sinister feeling too.
: I tried to highlight the nicest features, while creating nice contrast and darken less interesting areas at the same time. I had to match a pre-existing light setup, so it got even trickier, because I was constrained by the lights. I generally avoid flat lighting like hell, and I carefully place all my lights one by one.
: I followed the "rule of the thirds" as much as I could, avoiding placing the vehicle in the center if the image, too high or too low. I made it a third taller or shorter than the closest elements in the background, so it popped out a bit. Anything obstructing the reading of the silhouette was removed from the background too. I decided to remove some of the background elements I added in my first sketches, since they were distracting.
: The vehicle had a little more contrast than everything else; just to make it the center of attention a little more. On the other hand it had to be integrated into the surrounding environment too. So color correction of the passes with the vehicle was extremely important.
: The most important thing for make a composition believable is to have or create both background and foreground elements to surround the main asset. I couldn't do it here properly. There is just a hint of this in the second camera with the pebbles out of focus (Fig.19 - 20).