Abstract
Abstract. Geography markup language (GML) is an XML specification for expressing geographical features. Defined by Open Geospatial Consortium (OGC), it is widely used for storage and transmission of maps over the Internet. XML schemas provide the convenience to define custom features profiles in GML for specific needs as seen in widely popular cityGML, simple features profile, coverage, etc. Simple features profile (SFP) is a simpler subset of GML profile with support for point, line and polygon geometries. SFP has been constructed to make sure it covers most commonly used GML geometries. Web Feature Service (WFS) serves query results in SFP by default. But it falls short of being an ideal choice due to its high verbosity and size-heavy nature, which provides immense scope for compression. GMZ is a lossless compression model developed to work for SFP compliant GML files. Our experiments indicate GMZ achieves reasonably good compression ratios and can be useful in WebGIS based applications.
Highlights
Due to the unavailability of compiled Simple features profile (SFP) compliant Geography markup language (GML) 3 datasets, it has largely been prepared by making GML files SFP compliant or by converting shapefiles into SFP compliant GML files
GML is based on an abstract model of geography given by Open Geospatial Consortium (OGC) which defines the world in terms of features where each feature has a set of properties
Spatial properties are made up of one of the 12 geometry types and 10 subtypes provided in SFP
Summary
GML proves to be a great modelling language for geospatial web due to its advent from XML, a de-facto standard for web, which has the advantages of being human readable, browser friendly, extensible, editable and queryable. Based on the same idea, GQComp (Dai et al, 2009) uses a custom encoding for coordinates, makes provision for spatial and attribute data querying through the combination of featurestructure tree and R* tree spatial indexing; and achieves good compression. Another compression technique called Gtree (Harshita and Rajan, 2010; Harshita, 2013) restricted to work for only polygon data, uses a tree based structure for managing the coordinate data. The double-blind peer-review was conducted on the basis of the full paper
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