To create the Shadows, duplicate the footage and add a "tint" effect to it which will make it black and white and then mask out the area where the shadow is. Then add a curve effect and strengthen the black and white contrast and add an invert effect ontop of that.
The next thing to do was to add an adjustment layer, place it under the shadow layer and select "Luma matte shadow" which should make the shadow strongly visible. Then the last thing was to add a hue adjustment to try and adjust the colour of the shadow so it matches with the shadows in the scene.
The one major problem with this method was the fact that there wasn't enough room in the greenscreen room for the shadows to be fully displayed on the floor. So in the composited footage the shadow is partially cut off. As well as that, due to the stuff that was on the floor being used to try and replicate the bridge in the scene, the shadow isn't properly flat nor does it have the curvature of the bridge.
One other Post editing challenge that occurred was that in the alley shot, for what ever reason the tracked camera and the footage wouldn't line up very well, as the video footage was looking like it was sliding after being composited.
The way that this was fixed was simply keyframing and moving the footage so that it didn't slide using the leaf on the floor as the marker for the footage's position.
