Abstract
Oblique photogrammetry models are indispensable for implementing digital twins of cities. Geographic information system researchers have proposed plenty of methods to load and visualize these city-scaled scenes. However, when the area viewed changes quickly in real-time rendering, current methods still require excessive GPU calculation and memory occupation. In this study, we propose a data organization method in which we merged all quadtrees and used a binary encoding method to encode nodes in a merged tree so that the parent–child relationship between the tree nodes could be calculated using rapid binary operations. After that, we developed a strategy to cancel the loading of redundant nodes based on the parent–child relationship, which helped to reduce the hard disk loading time and the amount of memory occupied in visualization. Moreover, we introduced a parameter to measure the area of the triangle mesh per pixel to achieve unified data scheduling under different production standards. We implemented our method based on Unreal Engine (UE), and three experiments were designed to illustrate the advantages of our methods in index acceleration, frame time, and memory reduction. The results show that our methods can significantly improve visualization fluency and reduce memory usage.
Highlights
IntroductionGiven the necessity to cover city-scaled scenes in a digital twinning city, this method is absolutely noninvasive and can obtain high-precision models under various terrain conditions
In order to visualize oblique photogrammetry models, first, the entire area containing data is partitioned into blocks; each block is divided based on a quadtree, sometimes not strictly “quad”, and a copy of the data with different precisions is created on each node of the quadtree from the bottom to the top to build a tile pyramid model
To address the problems raised in Section 2.2.3, we conducted this research by improving the visualization process for a current oblique photogrammetry model, i.e., the data organization and a selection step
Summary
Given the necessity to cover city-scaled scenes in a digital twinning city, this method is absolutely noninvasive and can obtain high-precision models under various terrain conditions It is advantageous because it provides information on 3D geometry and ground texture [8] with low time and labor costs. Some researchers proposed visualization strategies including tile pyramid modeling, scene dispatch algorithm, and memory scheduling methods to exploit the transmission performance of the internet and the computational performance of the hardware Such approaches were successfully applied in Google Earth [17], Cesium [18], and other web-GIS platform projects to visualize city scenes. Geo-Inf. 2021, 10, 643 experiments with this prototype system and prove that the proposed methods improve the visualization efficiency and reduce the amount of memory occupied
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