Prof. Jun Li Profile

Prof. Jun Li

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Proceedings Article | 23 January 2024 Paper

An adaptive quadtree index reconstruction algorithm for massive 3D city models

Xiaoyun Shang, Qingren Jia, Jun Li, Yuying Pang, Quan Yang

Proceedings Volume 12978, 1297829 (2024) https://doi.org/10.1117/12.3020131

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Oblique photogrammetry models are organized in an index tree which incorporates the concept of Hierarchical Level of Detail (HLOD) for optimal rendering of spatial data in the widely used 3D Tiles specification. The inefficient data structure of the index tree, such as gird, may cause problems such as rendering delay and memory overflow on the client-side. This paper proposes an adaptive quadtree index reconstruction algorithm to construct an upper quadtree filled with virtual nodes for tiled tiles of a single oblique photogrammetry dataset using the named coordinates and the actual geographic coordinates of the tiles. The improved structure enables fast elimination of invisible tiles by exploiting the visibility relationship between parent and child nodes, thus improving the traversal rate of tiles. Experiments prove that the algorithm is effective in improving the loading efficiency of local tiles in a single tileset as well as tiles at the junction of multiple tilesets, which is applicable to most browsing scenarios. In addition, the algorithm minimizes the negative impact of the adaptive quadtree structure when observing panoramic tiles by adequately balancing the number of virtual nodes, the depth of the quadtree and the efficiency of tile culling, and experiments demonstrate that the time consumption is within an acceptable range, and the negative impact is insufficient to offset the positive effect of the performance enhancement.

Proceedings Article | 1 June 2023 Paper

Optimizing loading strategy for visualizing 3D photo-realistic model using human eye's area of interest

Yuying Pang, Qingren Jia, Jun Li, Anran Yang, Quan Yang, Xiaoyun Shang

Proceedings Volume 12710, 127100K (2023) https://doi.org/10.1117/12.2682649

KEYWORDS: Visualization, 3D modeling, Displays

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The 3D photo-realistic model is characterized by high accuracy and large data volume. When visualizing these data in GIS applications, the whole model will be tiled and pyramid for efficient network transferring and loading. Then the tile loading strategy based on the distance from the viewpoint (hereinafter referred to as “the distance-based strategy”) will lead to the tiles appearing at the edge of the screen own better visual quality and large volume compared with those in the center of the screen, which mostly been the primary area that attracts human attention. To address this data redundancy problem, this paper proposes a novel tile loading strategy method based on the human eye's area of interest which provides better visualization quality on the central area of the screen while keeping the overall data volume loading on the web. Compared to the distance-based methods, the proposed method considering the angular deflection of the direction from the camera position to the center of the tile and the LOS (light of sight) direction, and recalculating the screen space error (SSE) determines which tiles in the pyramid will be selected. This method can choose higher-resolution tiles for the center region and choose lower-resolution tiles for the marginal region simultaneously. The experimental results show it increases the screen resolution of the center area while keeping the memory occupation steady. This research can facilitate the applications of 3D photo-realistic models in digital cities.

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