5.3 Projection-based and spatial AR systems

Projection-based AR systems use projectors to overlay digital content onto real-world surfaces. This tech creates immersive experiences without headsets, using projection mapping, spatial AR, and CAVE systems for entertainment, education, and more.

Image correction techniques are crucial for projection-based AR. Geometric correction aligns images on non-flat surfaces, while radiometric compensation adjusts for varying surface colors and lighting, ensuring realistic and visually coherent augmentations.

Projection-based AR Systems

Projection Mapping and Spatial Augmented Reality

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• Projection mapping involves projecting digital content onto physical objects or surfaces to create immersive experiences
• Utilizes specialized software to map and align projected images with the contours and geometry of the projection surface (buildings, stages, objects)
• Spatial augmented reality (SAR) is a type of projection-based AR that augments the physical environment directly by projecting digital information onto real-world objects
• SAR eliminates the need for users to wear head-mounted displays or use handheld devices, enabling a more natural and seamless interaction with the augmented environment
• Applications of projection mapping and SAR include entertainment (live concerts, theater productions), advertising (product launches, interactive displays), and education (interactive exhibits, visualizations)

CAVE Systems and Projector-Camera Setups

• Cave Automatic Virtual Environment (CAVE) is an immersive projection-based VR/AR system that surrounds the user with projected images on the walls, floor, and ceiling of a room-sized cube
• CAVE systems typically use multiple high-resolution projectors to create a seamless 360-degree visual experience, allowing users to interact with the virtual environment using specialized input devices (wands, gloves)
• Projector-camera systems combine projectors and cameras to create interactive AR experiences
• The camera captures the user's interactions with the projected content, enabling real-time feedback and manipulation of the virtual elements
• Projector-camera systems can be used for applications such as interactive tabletops, collaborative workspaces, and augmented reality games

Image Correction Techniques

Geometric Correction

• Geometric correction addresses the distortion and misalignment issues that arise when projecting images onto non-planar surfaces
• Involves applying mathematical transformations to the projected image to compensate for the surface's geometry and ensure proper alignment
• Common geometric correction techniques include homography estimation, which calculates the projective transformation between the projected image and the desired output, and mesh-based warping, which divides the image into smaller patches and applies individual transformations to each patch
• Geometric correction is crucial for achieving accurate and visually coherent augmentations in projection-based AR systems

Radiometric Compensation

• Radiometric compensation deals with the photometric inconsistencies that occur when projecting images onto surfaces with varying reflectance properties and ambient lighting conditions
• Aims to ensure that the projected colors appear as intended, regardless of the surface's color, texture, or illumination
• Radiometric compensation techniques include color correction algorithms that adjust the projected image's colors based on the surface's reflectance properties, and intensity adjustment methods that modulate the projected light's brightness to compensate for ambient lighting
• Projector-camera systems can employ closed-loop feedback to continuously capture the projected image, compare it with the desired output, and adjust the projection in real-time to maintain consistent appearance
• Effective radiometric compensation is essential for preserving the visual fidelity and realism of the augmented content in projection-based AR applications