Guidelines for handling large amount of KML data
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The document discusses the use of Keyhole Markup Language (KML) at a GIS conference, highlighting its capabilities for geospatial data representation and the potential user base including geographers, biologists, and architects. It addresses challenges with KML file management, such as performance issues with large datasets, and proposes solutions like network links and regions for better data organization. The text also outlines existing tools and the need for practical guidelines to aid users in optimizing their use of KML.
Guidelines for handling large amount of KML data
- 2. • Keyhole Markup Language • Range of potential users • NetworkLink • Region • NetworkLink & Region • Existing solutions • My classification • Conclusions Overview 5th GIS Conference 29 May – 31 May 2014, Debrecen
- 3. • XML based language to describe features with geospatial information • Google Earth / Map • Generable by the application, but editable • Simple text file with kml (or kmz) extension • OpenGIS KML 2.2 Encoding Standard Keyhole Markup Language 5th GIS Conference 29 May – 31 May 2014, Debrecen
- 4. • Abstract elements with derived elements • Inheritance from ancestors • gx: Google extension namespace Class tree for KML elements 5th GIS Conference 29 May – 31 May 2014, Debrecen
- 5. Geometry 5th GIS Conference 29 May – 31 May 2014, Debrecen
- 6. • Geographers • Surveyors • Medical researchers, physicians • Epidemiologists • Biologists • Linguists • Agronomists • Architects • Catastrophe managers • Retailers • Etc. Range of potential users – motivation 5th GIS Conference 29 May – 31 May 2014, Debrecen
- 7. • Use the GUI of GE and save your features • Limited customization • Not all the KML elements are available The most simple way to create
- 8. • Hundreds of placemarks • Large files • Decreasing performance • Editing is hard • Solution • Divide and conquer • Network link & Region Issues 5th GIS Conference 29 May – 31 May 2014, Debrecen
- 9. • Simple element referencing another KML file or KMZ archive • The fetched KML file can contain • A hierarchy of Feature elements • One (optional) <NetworkLinkControl> element that controls the behaviour of the source (fetching) KML file. • A hierarchy of network linked KML files can be created. NetworkLink 5th GIS Conference 29 May – 31 May 2014, Debrecen
- 10. • For complex sets of KML files, you can partition the KML into multiple files that link to each other. • When data is changing frequently, the interval refresh feature of <NetworkLink> provides for timely refresh of the displayed data. • When data is distributed over a large area of the Earth’s surface, view-based refresh feature enables GE to perform a spatial search based on the current viewpoint and load only the data that is currently within the user’s view. • For very large data sets, the region feature allows you to control which parts of the data set are shown in a given view. Why to use Network Links? 5th GIS Conference 29 May – 31 May 2014, Debrecen
- 11. • Refers to a geographical area of 2D or 3D which extension is specified by its bounding 2D or 3D box. • Can be assigned to any KML feature • The features of a region are visible if the region itself is visible on the screen and it can be contained by a box with an edge length falling between two values specified as minLodPixels and maxLodPixels. Region 5th GIS Conference 29 May – 31 May 2014, Debrecen
- 12. • The networklink element has a viewRefreshMode subelement, which value has to be set onRegion to fetch the referenced file content according to the active status of the region. NetworkLink with Region 5th GIS Conference 29 May – 31 May 2014, Debrecen
- 13. • No tool in GE interface to define regions • Regionator • Free Python library to divide thousands of placemarks, polygons and paths into separate regions for better viewing. • Requires programming skills. Existing solutions 5th GIS Conference 29 May – 31 May 2014, Debrecen
- 14. • KML2KML • Commercial application with a number of tools for reorganizing and optimizing KML files. • Creates one single region to each checked feature types based on their minimal bounding boxes • No possibility to divide the features of the same type to several regions with different LOD values. Existing solutions 5th GIS Conference 29 May – 31 May 2014, Debrecen
- 15. • Further commercial applications (e.g. Arc2Earth) do exist. • Some companies offer services of creating data in KML format as well. • In spite of these opportunities, my personal experiences show that a practical guide is needed. Existing solutions 5th GIS Conference 29 May – 31 May 2014, Debrecen
- 16. The objectives of the most frequent usage methods related to placemarks are: • To reduce the number of placemarks packed closely together. • To separate different types of data into layers. • To fade features in and out of view. Objectives 5th GIS Conference 29 May – 31 May 2014, Debrecen
- 17. Regions with the same bounding box are used but with different LOD settings and the goal is to increase the number of visible features from the same area while zooming in. Features have to be grouped into several folders assigning the same bounding box to each of them. Case 1. 5th GIS Conference 29 May – 31 May 2014, Debrecen
- 18. • Increase the performance of rendering when the number of the futures is critical, but the aggregation level is acceptable . • Features have to be divided into separate files. • The main KML file contains references to the files with the help of network links. Every network link has an associated region, where the LOD can be even the same, but the bounding box match the physical extent of the features. • Computer does not have to manage data in memory, which are actually not visible, then the performance of our system will definitely grow. Case 2. 5th GIS Conference 29 May – 31 May 2014, Debrecen
- 19. • If the spatial distribution of the placemarks is approximately consistent then a classical quadtree structure is perfect to represent the nested regions. Case 3. 5th GIS Conference 29 May – 31 May 2014, Debrecen
- 20. I provided some practical guidelines by differentiating three cases, where instructions and explanations help the users without strong IT skills to manage large amount of data. Conclusions 5th GIS Conference 29 May – 31 May 2014, Debrecen
- 21. Thank you for your attention. 5th GIS Conference 29 May – 31 May 2014, Debrecen
Editor's Notes
- #4: Version 2.2 with the name of OpenGIS KML 2.2 Encoding Standard has been adopted as an OGC (Open Geospatial Consortium) implementation standard for presenting geographic information visually compressed
- #5: Elements to the right inherit the children of their ancestors (enszesztörs) to the left. As we are used to it abstract elelments (in box) cannot be created directly in a KML file.
- #7: Future trend is to use the geospatial component for visualization - My motivation is … The KML community is wide and varied: Scientists, teachers, students, average people, Surveyor – geodéta?
- #17: Three cases will be differentiated for the sake of simplicity.
- #18: Although technical references and manuals discuss this topic, my experiences show that the lack of programming experiences makes hard to implement the suggested strategies. Three cases will be differentiated for the sake of simplicity.