Projection mapping (PM) enables multiple users to experience virtual and augmented reality simultaneously with the naked eyes, making it valuable beyond traditional art and entertainment applications. It has been applied in various spatial augmentation domains, such as surgical assistance, object search, industrial design, remote communication, and human augmentation. However, achieving seamless spatial augmentation remains challenging due to PM’s limitations in bright environments and shadow interference during user interactions. Recent technical advancements in the PM research field have addressed these issues. Specifically, it explains a technique applying a multi-projector system that selectively illuminates areas other than the projection target, maintaining high contrast in a bright room. Light-field projectors simulate room lighting, enabling realistic shadow behavior. Shadow removal is achieved using large-aperture optics like micro-mirror array plates and Fresnel lenses. Future projection mapping systems must focus on simpler calibration methods and energy-efficient laser-based projectors to overcome remaining challenges. This talk introduces these technologies for seamless spatial augmentation.