Summary
Environmental issues can quickly become extremely complex. When dealing with site assessments, environmental remediation design or monitoring, public hearings, or environmental litigation, the quantity of data involved can quickly become overwhelming. Maintaining and organizing that data is insufficient. Visualization is the only means for condensing and communicating vast quantities of spatially referenced data. Whether the data consumer is an environmental engineer, geologist, or the public, visualization provides an invaluable tool to communicate complex data in a form that makes it intelligible to all parties.
This paper addresses the key issues related to the visualization of environmental data. Compiling the site data and ensuring that it is consistent, adequate and complete enough to be used is the first step. Beyond the data, the paper addresses the myriad of methods that can be applied to visualize, analyze and model the data.
Conscientious data visualization should begin with direct data visualization that displays the data with a minimal amount of interpretation or assumptions. The next stage of investigation and display involves gridding the data and interpolating and extrapolating the data to the nodes and/or cells of the grid. This process can be complicated by the incorporation of geologic information, site features (such as roads, buildings, and bodies of water), and aerial photography. These issues are addressed in detail in the sections below. Once the data is gridded and mapped to the grid, numerous examples are given of how to present this data visually. Presenting the data generally requires finding ways to delve into the data in three-dimensions. Usually this is performed using one or more data subsetting techniques.
Visualization is visual communication. It is the art and science of compressing and presenting information in a useful form that we humans can easily comprehend. Whether the data collected at an environmental site represents a portion of a page or bookshelves of reports, visualization can benefit everyone involved by transforming words and numbers into comprehensible images.
This paper is dedicated to the complex task of visualizing environmental data. There are many ways of visualizing data ranging from simple graphs, plots and charts to more representational two and three-dimensional visualizations and time varying animations. The focus of this paper will be representational graphics that portray the spatial characteristics of data. To this end, the data requirements associated with this paper will necessitate that all data have spatial information.
When approaching any new project that involves environmental data visualization, the first step is to assess the form and content of the data. Data is commonly delivered in many forms (which will be discussed in the next section). Assessing the content of the data can be done visually or as simply as evaluating basic statistics such as the number of samples, minimum, average and maximum data values, and the spatial extent.
The form of the data is usually governed by the application in which it was authored and/or stored. Typical applications include database software, Geographic Information Systems (GIS), spreadsheet programs and ASCII editors.
Environmental databases can be built in generic database software such as Microsoft Access or Oracle, or products like Earthsoft's EQuIS or Integrate's TerraBase, which are specifically developed to provide environmental data management for both chemistry and geologic data.
GIS programs like ESRI's ArcView provide database functionality that is inherently tied to spatial information. For that reason, GIS systems provide an ideal platform for storing and retrieving data to be used for environmental visualization. GIS files may also include maps that contain features such as roads, building outlines, rivers and other geographic features. Most GIS systems also provide some level of visualization capability though it is generally two-dimensional or limited three-dimensional.
Environmental databases and GIS systems generally contain far more information than is needed for the task of data visualization. The addition of sample/measurement date, laboratory, analytical methods, quality assurance information, well construction details, and name(s) of companies or individuals are just a few examples of information which may not be necessary to the task of visualization. However this additional data is often crucial to the documentation and defense of visualization tasks.
Spreadsheet programs like Microsoft's Excel are commonly used as the repository for environmental data. Their ease of use and ability to perform many database-like functions enhance their appeal. Spreadsheets can import and export most common data file formats including many database files.
ASCII (also known as text) files provide the most portable form for environmental data. Spreadsheets and databases can import and export ASCII files and they can be edited with a myriad of programs ranging from simple text editors (like Microsoft Notepad) to spreadsheets and databases. It is this portability that makes ASCII files a common choice as an input file format for environmental visualization.
Spatial environmental data if often contained in CAD (computer aided drafting) files. Many companies that take stereo-photography to provide topographic data deliver the results in CAD files. CAD files are also used to display roads, buildings and other site features. This data is most useful when the CAD files are drawn in the same, consistent coordinate system used for all other data.
Image files (also known as raster or bitmaps) are digital photographs. These photographs can range from snapshots of features on the site to ortho-rectified (requires that the image axes are parallel to the north-south and east-west coordinate axes) aerial photography. Snapshots merely provide documentation of site features and usually do not include any quantitative spatial information. Ortho-rectified photos can be used as texture maps. This allows them to be projected onto ground surfaces, geologic layers and/or buildings and other features in the visualization. In order to utilize a photo as a texture map we must be able to geo-reference the image. Some image file formats include geo-referencing information. This usually consists of the spatial coordinates of one corner of the image and the real-world size (both width and height) of a pixel. These formats include GeoTIFF, BMPW and TIFW (BMP & TIFF World Files). These file formats simplify the process of registering aerial photography. Some GIS software such as ESRI's ARC/INFO is capable of orthorectifying images that were not properly formatted.
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