Abstract
Geographic data sets are often very large in size. Interactive visualization of such data at all scales is not easy because of the limited resolution of the monitors and inability of visualization applications to handle the volume of data. This is especially true for large vector datasets. The end user’s experience is frequently unsatisfactory when exploring such data over the web using a naive application. Network bandwidth is another contributing factor to the low performance. In this paper, a Quadtree based technique to visualize extremely large spatial network datasets over the web is described. It involves using custom developed algorithms leveraging a PostGIS database as the data source and Google Earth as the visualization client. This methodology supports both point and range queries along with non-spatial queries. This methodology is demonstrated using a network dataset consisting of several million links.
The methodology is based on using some of the powerful features of KML (Keyhole Markup Language). Keyhole Markup Language (KML) is an Open Geospatial Consortium (OGC) standard for displaying geospatial data on Earth browsers. One of the features of KML is the notion of Network Links. Using network links, a wide range of geospatial data sources such as geodatabases, static files and geospatial data services can be simultaneously accessed and visualized seamlessly. Using the network links combined with Level of Detail principle, view based rendering and intelligent server and client-side caching, scalability in visualizing extremely large spatial datasets can be achieved.