Guidelines for handling large amount of KML data

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TÁMOP-4.2.2.C-11/1/KONV-2012-0001

Guidelines for handling large

amount of KML dataMarianna ZicharFIRST – Future Internet

Research, Services and Technology

TÁMOP-4.2.2.C-11/1/KONV-2012-0001

• 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

• 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


• Abstract elements with derived elements

• Inheritance from ancestors• gx: Google extension

namespace

Class tree for KML elements


Geometry


• Geographers• Surveyors• Medical researchers, physicians• Epidemiologists• Biologists• Linguists• Agronomists• Architects• Catastrophe managers• Retailers • Etc.

Range of potential users – motivation


• Use the GUI of GE and save your features• Limited customization• Not all the KML elements are available

The most simple way to create

• Hundreds of placemarks• Large files• Decreasing performance• Editing is hard

• Solution• Divide and conquer• Network link & Region

Issues


• 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


• 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?


• 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


• 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


• 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


• 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


• 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


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


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.


• 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.


• If the spatial distribution of the placemarks is approximately consistent then a classical quadtree structure is perfect to represent the nested regions.

Case 3.


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


Thank you for your attention.


Guidelines for handling large amount of KML data

Software

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