Progressive transmission of spatial data Prof. Wenwen Li School of Geographical Sciences and Urban Planning 5644 Coor Hall

Outline 1. Concepts 2. Progressive Media Data Transmission 3. Progressive Vector Data Transmission 4. Progressive Raster Data Transmission 5. Summary

Concepts Data Transmission Network (DTN)* A subscription-based service for the delivery of real-time information.* Market information Commodity cash prices News Weather report … *

Concepts Geospatial Information and Communication Technology (GeoICT) A technology extends Information Communication Technology (ICT) for geospatial information. Why GeoICT? The emergence of Internet The development of network-centric GIS Online geoprocessing Spatial web services Distributed computing and processing

Concepts Progress spatial data transmission Streaming: running and viewing the data in real time before fully downloading the content of this data. Progressive spatial data transmission: supports users to operate and view the spatial data in real time before fully downloading the content of this data.

Progressive Media Data Transmission Characteristics Massive multimedia data can be used immediately Offsets slow-speed Internet connections audio-on-demand or video-on demand Enables broadcasting historical and live presentations A ream of transmission between client and server

Progressive Media Data Transmission Work principle The media data is sent from the server to the client based on streaming While the part of the data is received, the pieced data is saved as a buffer on the local computer. When the minimal requirement of information has been satisfies, the media data can be operated on local computer

Progressive Media Data Transmission Technologies Two approaches to streaming: Web server based approach Steaming media server based approach

Progressive Media Data Transmission Technologies Differences between web server based approach and steaming media server based approach: The most of steps are similar, besides: Media files are compressed and produced in steaming media server The data is actively delivered to client from steaming media server Feedback can be replied by steaming server Steaming media server based approach can use the bandwidth better Steaming media server based approach can provide high-quality audio and video Stream media server based approach is more popular

Progressive Media Data Transmission Technologies Differences between web server based approach and steaming media server based approach: Steaming media server based approach is built based on the fundamental architecture of web server based approach Steaming media server based approach can use the bandwidth better Steaming media server based approach can provide high-quality audio and video Stream media server based approach is more popular

Progressive Media Data Transmission Compression Typical compression standards: Multimedia Content Description Interface (MPEG) 4: defined by the Moving Picture Experts Group (MPEG)

Progressive Raster Data Transmission Why raster data transmission? Digital images needs to be communicated over the Internet The size of image is becoming very large The transmission rate through Internet is low The load for accessing image is heavy Constrained communication bandwidths

Progressive Raster Data Transmission Methodology Progressive raster data transmission = Progressive image transmission (PIT): Spatial domain: focuses on the image objects or image sub-regions Image block Quadtree decomposition Multi-scales division Transform domain: focuses on the distribution of image frequency-domain Discrete Cosine Transform (DCT) Wavelet decomposition

Progressive Raster Data Transmission Compression Lossless compression algorithm: recovers all original information during the decompression phase. Contains all information The cost is the maximum achievable compression ratio Lossy compression algorithm: recovers original information by high compression ratio Lost information The cost relies on computational requirement

Progressive Raster Data Transmission Typical compression standard JPEG2000 Compression and Transmission Standard Most commonly standard for image compression and transmission Compression with Reversible Embedded Wavelets (CREW) Applies wavelet-based algorithms Wavelet-based Progressive Image Transmission (PIT) Very high resolution raster data may beyond the client’s capability of displaying image Lacks a definition for client-server communication Lacks protocol for stream transmission

Progressive Raster Data Transmission Single-rate transmission vs. progressive transmission *

Progressive Raster Data Transmission Advantages Enables viewing the image before it is fully received Enables decompressing the image for display

Progressive Vector Data Transmission Why vector data transmission? Geographical features needs to be collative analyzed over the Internet The pattern of geometry is becoming very complex The transmission rate through Internet is low The load for accessing vector data is heavy Constrained communication bandwidths Strategies: High performance architecture: increases computing speed Parallel computing: computes simultaneously

Progressive Vector Data Transmission Progress spatial data transmission Similar idea to raster data transmission: encoding data & decoding data Cannot be realized by single algorithm and single technique Requires integrated techniques Demands the theories and techniques from cross-domains

Progressive Raster Data Transmission Compression Lossless compression algorithm: recovers all original information during the decompression phase. Lossy compression algorithm: recovers original information by high compression ratio Factors affected compression:* reducing the amount of coordinate information reducing the data structure to more compact, less storage-intensive, forms * McMaster, R. B., & Shea, K. S. (1992). Generalization in digital cartography. Washington, DC: Association of American Geographers.

Progressive Vector Data Transmission Methods Spatial domain: Depending on the request including layer information and spatial extent, the server would send the divisions of spatial objects in this spatial extent to client. Main steps: Filter Step: approximate spatial extent for each spatial object (e.g. minimum bounding boxes-MBB) are used to filter the result cannot be part of client’s request. Refinement Step: each spatial objects obtained after filtering is further examined by computational algorithm.

Progressive Vector Data Transmission Methods Spatial domain: How to improve the performance of progress vector data transmission?* Spatial indexing algorithms little contribute to improving the performance of spatial data transmission over Internet The performance of server will be counteracted by bandwidth Should focus on strategies on data transmission reduction by spatial access methods (SAMs)* Shorten data downloading time Improve the downloading performance * Bertolotto, M., & Egenhofer, M. J. (2001). Progressive transmission of vector map data over the world wide web. GeoInformatica, 5(4),

Progressive Vector Data Transmission Methods Detail (LoD) domain: Different resolution (details) for spatial object is stored in server for representation based on request. Mainly from map generalization Line simplification Vertices

Progressive Vector Data Transmission Example *

Summary Geospatial information and communication technology Progressive spatial data transmission Progressive media data transmission Progressive vector data transmission Progressive raster data transmission