Computers & Geosciences 72 (2014) 176–183 Contents lists available at ScienceDirect Computers & Geosciences journal homepage: www.elsevier.com/locate/cageo Moving KML geometry elements within Google Earth Liang-feng Zhu n, Xi-feng Wang, Xin Pan Key Laboratory of GIS, East China Normal University, Shanghai 200241, China article info abstract Available online 1 August 2014 During the process of modeling and visualizing geospatial information on the Google Earth virtual globe, fi Keywords: there is an increasing demand to carry out such operations as moving geospatial objects de ned by KML Virtual globe geometry elements horizontally or vertically. Due to the absence of the functionality and user interface Google Earth for performing the moving transformation, it is either hard or impossible to interactively move multiple KML geospatial objects only using the existing Google Earth desktop application, especially when the data Moving transformation sets are in large volume. In this paper, we present a general framework and associated implementation Geometry element methods for moving multiple KML geometry elements within Google Earth. In our proposed framework, we first load KML objects into the Google Earth plug-in, and then extract KML geometry elements from the imported KML objects. Subsequently, we interactively control the movement distance along a specified orientation by employing a custom user interface, calculate the transformed geographic location for each KML geometry element, and adjust geographic coordinates of the points in each KML objects. And finally, transformed KML geometry elements can be displayed in Google Earth for 3D visualization and spatial analysis. A key advantage of the proposed framework is that it provides a simple, uniform and efficient user interface for moving multiple KML geometry elements within Google Earth. More importantly, the proposed framework and associated implementations can be conveniently integrated into other customizable Google Earth applications to support interactively visualizing and analyzing geospatial objects defined by KML geometry elements. & 2014 Elsevier Ltd. All rights reserved. 1. Introduction environment from the low level, users of Google Earth only need to describe and save their own geospatial information in formats Nowadays a series of sophisticated and powerful online virtual according to the OpenGIS KML Encoding Standard, and the Google globes, led by Google Earth, are becoming reliable platforms for Earth virtual globe can effectively load and vividly visualize that communicating, analyzing and sharing geospatial information that information over the Internet (Zhu et al., 2014). is large-extent, multi-scaled, multi-source, massive and heteroge- In recent years, several earth scientists and industry developers neous (Butler, 2006; Bailey and Chen, 2011; Goodchild et al., 2012; have launched a series of explorations on how best to model and Yu and Gong, 2012). The Google Earth virtual globe has been widely visualize geospatial information within Google Earth using KML fi embraced by earth scientists, educators, government of cials and (Whitmeyer et al., 2010; Bailey et al., 2012; Stewart and Baldwin, the general public as an important and everyday tool to conduct 2012; Martínez-Graña et al., 2013; Wang et al., 2013). For example, research, exchange ideas and share knowledge with a global De Paor and Whitmeyer (2011) have described a variety of perspective in a natural and intuitive way, mainly because it techniques and methods through which KML can be used to possesses the ability to support the OpenGIS KML Encoding control the visualization of geological and geophysical data on Standard (OGC KML) (Wilson, 2008; Ballagh et al., 2011; De Paor Google Earth, and presented a method to create dynamic models et al., 2012; Lee and Guertin, 2012). As an open data standard for that illustrate the internal structure of the Earth by using COLLADA encoding representations of geospatial information visually, KML and JavaScript. Postpischl et al. (2011) addressed the problem of enables users of Google Earth or other geo-browsers to add custom the standardization and visualization of seismic tomographic geospatial data to virtual globes in a variety of formats, and allows models and earthquake focal mechanisms data sets using web users to create a variety of powerful user interface controls that technologies and KML. Blenkinsop (2012) has used a macro- interact with their own data (De Paor and Whitmeyer, 2011). enabled Excel workbook to convert field data into KML documents Without having to develop a more sophisticated 3D/4D virtual for the purpose of representing structural geology in Google Earth. Zhu et al. (2014) presented an automatic method for modeling and n visualizing large volume of borehole information on Google Earth Corresponding author. Tel.: þ86 13671721009. E-mail addresses: [email protected] (L.-f. Zhu), using KML. The above-mentioned advances have achieved suc- [email protected] (X.-f. Wang), [email protected] (X. Pan). cesses to a greater or lesser extent in specific fields of use, which http://dx.doi.org/10.1016/j.cageo.2014.07.016 0098-3004/& 2014 Elsevier Ltd. All rights reserved. L.-f. Zhu et al. / Computers & Geosciences 72 (2014) 176–183 177 also played significant roles in promoting the development and This script can be utilized to move continental components, crustal professional application of the Google Earth virtual globe. fragments and other geological structures for tectonic reconstruc- After a thorough evaluation of the applications, we have tions. However, due to the limitation of the implementation program, detected several serious limitations when using the existing this script seemed to lack the flexibility since it only supports the Google Earth desktop application and its user interface controls command-line (console) operation to process KML files. That is, users to model, visualize and analyze geospatial information. One of the could neither move KML objects interactively nor control the move- current main shortcomings of Google Earth is its inability to mentdistancethroughanefficient graphical user interface. By using represent the underground space of the Earth (De Paor and the Google Earth web plug-in and its JavaScript application program- Whitmeyer, 2011; Navin and de Hoog, 2011). Technically speaking, ming interface (API), Dordevic (2013) has designed a webpage Google Earth only provides a 2.5D digital globe that ideally suited (http://www.digitalplanet.org/API/SOS/index.html), which embeds for the modeling, visualization and analysis of geospatial informa- interactive screen overlays as custom sliders, to control COLLADA tion relevant to the Earth's surface and near-surface. Therefore, it models to emerge from the subsurface. This webpage has proven to is unable to directly display or analyze subsurface objects/phe- be quite effective for handling 3D COLLADA models, but it could not nomena/processes in the correct locations beneath the Earth's be expanded to deal with other types of geospatial objects. In brief, surface. In order to model, visualize and interpret subsurface up to now there are still no comprehensive methods or systematic features, some elegant tricks need to be designed and applied to applications for moving various types of geospatial objects within bring subsurface information into view. Recently, two techniques Google Earth. Therefore, there is a clear need for developing a have been developed to address the needs of visualizing the universal method to handle all types of KML objects. subsurface. One technique is to set an uplifted height value for In this paper, we explore the transformation techniques and the purpose of elevating the vertical position of subsurface associated implementation methods for moving KML geometry features and to make them visible above the Earth's terrain surface elements within Google Earth. Our ultimate goal is to present a (De Paor and Whitmeyer, 2011; Zhu et al., 2014). This is a static general framework for the moving transformation, which is way of elevating subsurface models into view, and has the suitable to deal with all types of KML geometry elements freely advantage of easy to implement. However, in this way, it is either and flexibly. This paper first summarizes the classification and the hard or impossible to interactively move subsurface features description of KML geometry elements, as well as the method for because their altitudes would be fixed after lifted. A second defining their geospatial positions. Subsequently, the overall approach is to pre-generate a set of KML objects containing KML framework and key steps for performing the moving transforma- 〈TimeSpan〉 tags with sequential increased altitudes, and to exploit tion are illustrated in great detail. The implementation program the built-in Google Earth time slider control to raise objects up out and its application are finally presented. of the surface (De Paor and Pinan-Llamas, 2006; De Paor and Williams, 2006; De Paor et al., 2008; De Paor and Whitmeyer, 2011; Dordevic, 2012). This approach provides high quality anima- 2. KML geometry elements tion capability with visually appealing appearances, but suffers from the huge data redundancy. Moreover, the built-in Google In digital globes, geospatial objects are generalized as points, Earth time slider is originally designed for controlling time lines, polygons and other types of geometry elements. As listed in intervals of displaying KML objects, thus it is