Linking OGC Web Services to Google Earth

Abstract

KML, or Keyhole Markup Language, is an XML grammar and file format for modeling and storing geographic features such as points, lines, images, and polygons for display in Google Earth (GE). On the other hand OGC (Open Geospatial Consortium) defines a similar format: GML, or Geographic Markup Language which is used as data encoding for other OGC standards such as Web Map Service (WMS) and Web Feature Service (WFS). KML is almost consistent with GML but KML has dynamic features which make possible the control over the loading of its content over the Web. This work designs and implements a transformation service called G2K which transforms spatial data published through OGC services to KML. Not as simple as a format converter, G2K sequences its operations: GML request, GML to KML conversion, and KML streaming on one piece of data at a time smartly using above dynamic KML features and OGC filter encoding. Thus G2K can be used as a middle layer to link OGC servers and GE. For users having commercial GE professional version which can connect to WMS, G2K is still beneficial because one sometimes needs a customized transformation. Our demonstration with biological satellite imagery (NOAA AVHRR Vegetation Index, ASTER and MODIS Evapotranspiration) and 3D buildings on GE client justifies this point