Previs (previsualization) and techvis (technical visualization) are both important scene-planning processes for modern filmmaking. Previs happens first and involves planning how a scripted scene or sequence of scenes should look using sketches, photographs, storyboards, animatics, or even rough 3D animations.
Using the previs materials, techvis artists then plan out the more technical process of how to capture the creative visions outlined in the previs. Techvis helps inform the director and crew about camera position, actor placement and movement, lighting setups, greenscreen measurements and positions, set details, and more.