As a real-time compositing system, Previzion renders a live video in 3D coordinates in 3D space. this means that there are a few ways of treating the incoming live video to achieve the desired effect.
By default, the incoming video, or video plane, is as close to the virtual camera as possible. In the interface, this setting is called Subject Depth and is measured in centimeters.
In Previzion build 7686 and above, the minimum distance is 25.0 centimeters.
By moving the Subject Depth to a longer distance, the live video input is placed further away from the virtual camera, projecting out from the lens’ nodal point.
This allows you to place the incoming live video behind and in between objects. This is very useful for adding people behind virtual elements or inside virtual vehicles, for instance.
Fix Subject Depth to a location
As of build 7686, there is the option of creating a mark to which the video plane stays fixed to. Ordinarily, the video plane distance is fixed to the camera.
The Set Depth As Camera to Marker option allows you to make the video plane to always be in the same location relative to the scene.
This is the same Survey Markers that are located in Mattes Tab.
To use this feature:
- Start by surveying or measuring where you would like to create a marker. You may do this using a survey tool or adjusting a marker and using parallax to judge the position of the marker.
- Create a new survey marker by pressing “Add.” Name you marker and enter the coordinates for the desired position.
- Back in Camera Tab, check the box to enable Set Depth As Camera to Marker and select the marker to which it will be fixed to. The marker does not need to be enabled or showing for this feature to work.
Near and Far Clipping Planes
Like other compositing applications that use 3D CG scenes, Previzion has setting for limiting the range between which things are rendered. By default this is set to Set Clipping Automatically, which essentially renders all elements in your scene.
If for some reason you need to change the clipping planes, uncheck this option and enter new values manually. This can be used if, for example, a virtual wall is close to the camera and blocking the scene, uncheck Set Clipping Automatically and set the near and far clipping planes.