The foreground and background is combined in a composition program (we use After Efffects) to see if the scales, sizes and camera movements match. The test composite below uses a low resolution version of Santa to speed up render times.

The image and the video both displayes a glaring problem: while the camera movement and sizes match nicely, the models do not fit together. There are large holes in the ground. This is because we changed the camera angle after the background was built. You do have to be careful. Finally we lowered the camera angle somewhat and added a few snowy hills to the background.