3D WebGIS: From Visualization to Analysis. An Efficient Browser-Based 3D Line-of-Sight Analysis
Abstract
:1. Introduction
1.1. Why Do We Need WebGIS?
1.2. The Research Challenges of WebGIS
2. Related Work
2.1. History and Current State of 3D WebGIS
2.2. 3D Line-of-Sight Computation
2.3. WebGIS Performance Research
3. Methods
3.1. Creating a LiDAR-Inspired Artificial Test Dataset
3.2. Test Environment
3.3. A Browser-Based 3D Line-of-Sight Analysis
3.3.1. Definition
3.3.2. Aims and Strategies
3.3.3. Two Levels of Optimization
- The layer-levelThe inter-layer-optimization makes use of two principles. First, the algorithm examines static layers before tiled layers. Static layers are not tiled or requested by grid-based bounding boxes but instead consist of objects that are loaded at once and afterwards are constantly kept in the client memory for visualization. Static layers are useful to add specific objects to a scene that are not too big in data size but are required for individual visualizations or analyses, e.g., a model of a planned building in a cityscape. Second, the search space that has to be examined in subsequent tiled layers will be reduced by the results of the previously examined static and other tiled layers. Between the examination of two layers, the target point parameter of the next layers analysis is adjusted to the closest obstacle intersection found in the previous layer. This reduces the search distance and thus the number of tiles that have to be downloaded and analyzed during the next layer check.
- The tile-levelOn the tile-level (intra-layer-optimization), three strategies can be applied to optimize performance. First, the chunked (i.e., tiled) nature of the data allows loading just a necessary subset of the whole dataset, and thus enables data streaming. Data partitioning is a crucial strategy to be able to handle very large datasets and to process it piecewise. Second, some tiles that have to be analyzed may already be found in the client cache (because they were loaded earlier either for visualization or for another earlier analysis) and can be accessed and analyzed fast. Such cached tiles can be accessed and analyzed very fast and should be prioritized when determining the sequence of tiles to be analyzed. A sorting of the tiles by being cached or uncached and starting the analysis with the cached ones, which can reveal a new closest intersection, that can, similar to in the layer level, be used to reduce to search space and reduce the number of uncached tiles that have to be loaded, separates the analysis in a faster and a slower part. If during the fast part an intersection with the line-of-sight can be found, all slow parts (uncached tiles) that lie behind that intersection can be skipped and thus improve the overall performance. Third, the remaining uncached tiles can now be requested asynchronously, which means that, depending on current browser implementations, 6–13 parallel connections can be established from the browser to resources of the same Internet domain [39] (host server addresses of the data services) to download the pending data. Thus, some of the server and network load can be handled in parallel to speed up the process.
4. Discussion of the Results
4.1. Performance
4.2. Scalability
5. Conclusions
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
References
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Auer, M.; Zipf, A. 3D WebGIS: From Visualization to Analysis. An Efficient Browser-Based 3D Line-of-Sight Analysis. ISPRS Int. J. Geo-Inf. 2018, 7, 279. https://doi.org/10.3390/ijgi7070279
Auer M, Zipf A. 3D WebGIS: From Visualization to Analysis. An Efficient Browser-Based 3D Line-of-Sight Analysis. ISPRS International Journal of Geo-Information. 2018; 7(7):279. https://doi.org/10.3390/ijgi7070279
Chicago/Turabian StyleAuer, Michael, and Alexander Zipf. 2018. "3D WebGIS: From Visualization to Analysis. An Efficient Browser-Based 3D Line-of-Sight Analysis" ISPRS International Journal of Geo-Information 7, no. 7: 279. https://doi.org/10.3390/ijgi7070279