Knowledge Base

Preparing Your Scene

What is a Previz scene ? #

This example will walk you through the right way to prepare a scene for Previz. This simple project simulates a stage with two tall screens in the back (grouped as a screen_sides mesh), an assembly of several smaller screen as a main screen (screen_main) and third mesh for the stage.

Prepare Scene 01
The scene: two sets of screens and a stage

What a Previz scene consists of ? #

A Previz scene consists of a collection of:

  • Objects (3D meshes) representing the physical elements of a scenes (screens, stages, buildings, props...)
  • Mappings (UV sets) describing the different ways objects are textured
  • Assets (images and videos)

Note: other elements (cameras, lights, materials, normals...) are not exported nor meaningful for Previz.

An example scene #

Our little project has 5 different mappings:

Prepare Scene 02
`stage` is only applied on the `stage` mesh. It will be used within Previz to apply a static texture to the props. In this example just an Ambient Occlusion pass has been baked into a texture, but any other techniques like Image Based Lighting can be used to enhance the look of those static objects.
Prepare Scene 03
`direct_main` fully maps a 16:9 asset to the `screen_main`.
Prepare Scene 04
`single_main` maps only one of the smaller screens of `screen_main`.
Prepare Scene 05
`sides_direct` maps a narrow content to both the side screens.
Prepare Scene 06
`planar` is planar projection from the point of view of the audience to all the screens. As such, this mapping exists for both `screen_main` and `stage` meshes.
Prepare Scene 07
`planar` is planar projection from the point of view of the audience to all the screens. As such, this mapping exists for both `screen_main` and `stage` meshes.

Important note: mappings that affect several objects must have the exact same names for each mesh.

Prepare Scene 08

Simplifying the scene #

In general, it is better to limit the number of meshes as much as possible by joining related parts together: the less meshes, the less default mappings have to be set in Previz. Here, we could have had two different meshes for each side screen. But as both screens same the exactly the same mappings, they form a well defined logical group of objects: it makes sense to join them to a single mesh.

Keep an eye on the number of vertices of your meshes: the bigger the mesh, the lower Frame Per Seconds Previz will reach. Exports from CAD software, LIDAR and point clouds are notoriously generating over-complex objects. Try to simplify your geometries as much as possible. CAD and LIDAR exports also tend to generate non-manifold meshes, orphan vertices that don't describe polygons, inner-faces and sometimes unusuable overlapping UV sets. Be sure to clean those models: usually they won't affect the look of your scene, so it is not obvious at first that they have an impact on performances.

Previz expects the center of gravity of the scene to be located at the origin of the coordinate system: make sure to recenter your scene around the (0, 0, 0) coordinate.

Checklist before exporting to Previz #

  • Geometries from CAD / LIDAR have:
    • No orphan vertices
    • Only manifold objects
    • No inner faces
  • Objects are logically regrouped into single meshes
  • Each mesh has an unique name
  • UV sets are properly named:
    • Mapping unique to a single mesh have an unique name
    • Mappings shared betwen several meshes have the exact same name
  • A nice props look is baked into a texture

After checking these points, the scene is ready to be exported to Previz.

Installing the Cinema 4D Addon Viewer