Keyhole Markup Language (KML)
Christopher Abplanalp
COMP 436 - XML
August 1, 2009
Keyhole Markup Language (KML)
Keyhole Markup Language (KML) is an XML data-formatted language used to display geographic annotation and visualizations of the Earth on the web. In addition, KML is a human readable language, read through an Earth browser similar to the way HTML is read by web browsers. Composed of text and punctuations, KML may receive revisions through the use of a simple text editor prior to publication. Based on a combination of research and experience, users can create powerful presentations by painting unique, or individualized, geographical data with limited programming knowledge. Today I plan to address the following issues pertaining to Keyhole Markup Language: the history of KML and its development, the structure/schema behind its code, some tools and applications that use KML, the advantages/disadvantages of the language, and what the future holds for KML (Warnecke).
In 2001, a company named Keyhole Earthviewer 1.0 first developed Keyhole Markup Language. Google acquired Keyhole in 2004 and renamed the software Google Earth. Within the past five years, KML’s status has skyrocketed. KML is now the international standard for presenting geographical information visually. The official name for KML is the OpenGIS KML 2.2 Encoding Standard (OGC KML), which is managed by the Open Geospatial Consortium. (Warnecke). According to Warnecke, tens of millions of KML files are currently shared on the web. Although KML may seem similar to Geography Markup Language (GML), its predecessor, KML is more of a presentation mapping language while GML represents geographical objects. Using KML
construct, users may implement GML in order to style the language according to KML presentation standards (www.ogleearth.com).
Users are exploring the advantages of this language system for a variety of reasons. Many individuals use KML to placemark their homes, trips, and biking routes. Students and teachers further use KML to explore people, places, and events, both historical and current. Finally, KML may benefit all housing professionals (i.e. real estate, architects, and city development agencies) attempting to visualize plans for a variety of projects, as well as scientists attempting to map out models and trends of volcanic eruptions, weather patterns, earthquake activity, and mineral deposits (Warnecke). KML is used by so many due to the simplicity and structure of the code.
To begin a KML file, users insert the following two lines of code: (1) and (2) tag at the end of the document. Some other tags that help develop the KML are the tag, which has children tags of , , and . The element contains tags, which enclose the value of the longitude, latitude, and altitude of the . Since KML is an XML data format, it stays consistent with patterns of angle brackets “< >” around the elements. KML also uses both a simple and a complex element, which means that when an element starts with a capital letter (i.e. ) it will contain other elements inside of that element (i.e. ) making it a complex element. If, however, the element does not start with a capital letter (i.e. ), it is considered a simple element. This idea is similar to XML: the complex elements resemble the parents while the simple elements reflect the children (Warnecke). The KML schema, provided online by Google, is a long and detailed document (over 1600 lines of code), which shows how these complex and simple elements should be used. After reviewing the schema, it appears as though the code is highly organized; the simple elements are declared first, followed by the stand-alone elements, and lastly the complex elements, which contain the different sequences of
elements for that complex type. Some applications using KML use the provided schema while others alter the schema for their application needs.
The main applications, which use KML, are Google Earth and Google Maps. Both applications have the ability to read KML files and display the results geographically on their prospective maps. ArcGIS Explorer is another application that uses KML to display geographical spatial representations. The well-known photo sharing website, Flickr, further uses KML by geotagging the images and displaying them in Google Earth. Microsoft Virtual Earth (Bing Earth), which is a very similar application to Google Earth, uses KML as well. Additionally, NASA uses KML in their application called World Wind. World Wind is a scientist and student programmer application, which gives users greater detailed overlays of certain locations. ) Various other applications also rely on KML, while (
others continue to develop daily. KML is a language that will continue to grow and advance with time.
KML has many advantages. First of all, KML is that a language that is very simple to learn while creating documents from scratch. Secondly, importing existing KML documents is relatively easy to do with the use of various applications - most notably Google Earth. Based on research and experience, KML has a few disadvantages, which should be taken into consideration. For example, depending on the size of the KML, some graphics will not render correctly. The reason behind this is that Google only allows a Maximum of 3MB for KML files. (Udell) Depending on the application in question, the type and severity of advantages and disadvantages concerning KML will vary; however, all inconveniences considered, KML is a language that will continue to see major growth in upcoming years.
KML has many great things in store for the future. For instance, KML will enable researchers to conduct census data across the world and collect accurate information. Additionally, KML will help implement some new infrastructure that crosses the domains of the heavy duty and lightweight geospatial web. Finally, KML will help build upon an already large-scale data sharing and linking, geospatial and data visualization mechanisms and tool development, web native API integration and community building.
() This open OGC KML standard is going to continue
advancing through the years and will only improve with time.
浙公网安备 33021202002483