Tile-Based Geospatial Information Systems

Transcription

1 Tile-Based Geospatial Information Systems

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3 John T. Sample Elias Ioup Tile-Based Geospatial Information Systems Principles and Practices 123

4 John T. Sample Naval Research Laboratory 1005 Balch Blvd. Stennis Space Center, MS USA Elias Ioup Naval Research Laboratory 1005 Balch Blvd. Stennis Space Center, MS USA ISBN e-isbn DOI / Springer New York Dordrecht Heidelberg London c Springer Science+Business Media, LLC 2010 All rights reserved. This work may not be translated or copied in whole or in part without the written permission of the publisher (Springer Science+Business Media, LLC, 233 Spring Street, New York, NY 10013, USA), except for brief excerpts in connection with reviews or scholarly analysis. Use in connection with any form of information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed is forbidden. The use in this publication of trade names, trademarks, service marks, and similar terms, even if they are not identified as such, is not to be taken as an expression of opinion as to whether or not they are subject to proprietary rights. Printed on acid-free paper Springer is part of Springer Science+Business Media (

5 To Nicole and Oliver - John Sample To Sarah and Georgette - Elias Ioup

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7 Preface Tile-based mapping systems have grown to become the dominant form of mapping system with the rise of Web-based mapping tools. The origin of this book is a desire to collect all our discoveries, techniques, and best practices for creating a tiledmapping system into one combined volume. The intent of this text is to provide a comprehensive guide to the theory behind creating a tiled-map system as well as a practical guide to create a concrete implementation. Stennis Space Center, MS May 2010 John Sample Elias Ioup vii

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9 Acknowledgements The authors would like to thank the Naval Research Laboratory s Base Program, program element number N, for sponsoring this research. Additionally, the following people provided technical assistance without which this book would not have been possible: Perry Beason, Frank McCreedy, Norm Schoenhardt, Brett Hode, Bruce Lin, Annie Holladay, Juliette Ioup, and Hillary Mesick. ix

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11 Contents 1 Introduction Background of Web-Based Mapping Applications Properties of tile-based mapping systems Book Organization Logical Tile Schemes Introduction Global Logical Tile Scheme Blue Marble Example Mercator-Based Schema Variable Start Tile Schemes Standardized Schema References Tiled Mapping Clients Tile Calculation Discrete Map Scales Continuous Map Scales Tile Retrieval Local Tile Storage Network Tile Retrieval Generating the Map View Discrete Scales Map View Continuous Scales Map View Example Client Survey of Tile Map Clients Image Processing and Manipulation Basic Image Concepts Geospatial Images Specialized File Formats xi

12 xii Contents 4.3 Image Manipulation Interpolation 1: Nearest Neighbor Interpolation 2: Bilinear Interpolation 3: Bicubic Choosing Image Formats for Tiles Choosing Tile Sizes Tuning Image Compression References Image Tile Creation Tile Creation from Random Images Tile Creation Preliminaries Bottom-Up Tile Creation Choosing the Base Level for a Set of Source Images Pull-Based Versus Push-Based Tile Creation Tile Creation Algorithms Scaling Process for Lower Resolution Levels Optimization of Tile Creation Caching Tile Sets in Memory to Improve Performance Partial Reading of Source Images Reading Random Areas from Source Images Tile Creation with Partial Source Image Reading Tile Creation with Parallel Computing Multi-Threading of Tile Creation Algorithms Tile Creation for Distributed Computing Partial Updating of Existing Tiled Image Sets References Tile Storage Introduction to Tile Storage Storing Image Tiles as Separate Files Database-Based Tile Storage Custom File Formats Comparative Performance Writing Tests Reading Tests Storage of Tile Metadata Storage of Tiles in Multi-Resolution Image Formats Memory-Cached Tile Storage Online Tile Storage...127

13 Contents xiii 8 Practical Tile Storage Introduction to Tile Indexes Storage by Zoom Level Introduction to Tile Clusters Tile Cluster Files Multiple Levels of Clusters Practical Implementation of Tile Clusters Application to Memory Cached Tiles Application to Distributed Computing Performance Optimizations of Tile Cluster Method Tile Serving Basics of HTTP Basic Tile Serving Tile Serving Scheme with Encoded Parameters Tile Serving Scheme with Encoded Paths Service Metadata Alternatives Conclusions References Map Projections Introduction to Datums, Coordinate Systems, and Projections The Shape of the Earth Datums Coordinate Systems Map Projections Different Map Projections Cylindrical Equidistant Projection Cylindrical Equal-Area Projection Mercator Universal Transverse Mercator Point Reprojection Map Reprojection Affine Transforms Interpolation Point-wise Reprojection Tablular Point-Wise Reprojection Map Projections for Tiled Imagery Storing Tiles in the Geodetic Projection Storing Tiles in the Mercator Projection Other Projections Which Projection for a Tiled-Mapping System? Conclusion References...191

14 xiv Contents 11 Tile Creation using Vector Data Vector Data Tile Creation Queries Storage Database Storage File System Storage Case Study: Tiles from Blue Marble Imagery Pull-Based Tiling Push-Based Tiling Results Case Study: Supporting Multiple Tile Clients KML Server Static KML Example Dynamic KML Example WMS Server WMS Servlet Implementation References Index...235