This is something fundamental that needs to be done in order to work with Lumion. In simple terms, Lumion does not recognize your geometry, but instead recognizes the materials assigned to each surface or face. To help you understand, let's have a look at the following image:

In the previous image, we have a 3D model that only has one material which, in this case, is the default material used by 3ds Max. So far so good, but watch what happens when we import the same model in Lumion and try to add a Lumion material. The image at the bottom-right corner shows the result of using only one material for the entire model—Lumion only recognizes "one big surface".

For that reason, you need to think ahead and identify which areas of your model need a specific material and you need to assign a different material for each section. As you can see in the following screenshot, it doesn't need to be something too fancy:

In this case, a simple colored material was applied to the different sections. For example, for the windows, we used a blue material; for the walls, a green material; and so on.

With all of these things in mind, you are now ready for a quick overview of Lumion and are ready to find out how it works. It is a crash course in two pages, but it will provide you with all you need to know to follow the rest of the book.