Visualization of environmental data in EVS involves six fundamental steps:
1) Read and pre-process the geologic and/or analytical data to clip the data values into the ranges of interest, and to log transform the data when appropriate;
2) Krige the data to produce two- or three-dimensional grids of data values;
3) Filter the data to produce subsets which contain the regions and ranges of interest, and map the filtered data to a color range appropriate for the visualization objective;
4) Apply mapping and coloring techniques to display data as slices, edges, faces, isolines, surfaces, plumes, glyphs, streamlines, stream-ribbons, etc.;
5) View the output in 3-dimensional space with dynamic rotation, translation and zooming to visualize and emphasize the characteristics of interest in the data set;
6) Output selected views to digital image files (4DIMs, images and animations) for production of hardcopy or video animations (Animation is only available in EVS-PRO and EVS.).
EVS has been designed to provide streamlined reproducible methods to complete visualization and analyses. The modular structure of the program allows the user to graphically construct their own visualization programs, which can be saved as applications for subsequent use with the same or different data sets.
EVS provides automated data preprocessing in all of its kriging modules, and in stand-alone modules, which allow the user to clip a data set to within specified limits, and to take the log base 10 of the data values. Many environmental data sets contain a mixture of geologic and hydrologic data, which are generally smooth and continuous throughout a domain, and chemistry data commonly varies over several orders of magnitude across short distances. Therefore, EVS provides the capability to quickly preprocess these data sets, thus greatly enhancing the scientist’s ability to analyze and visualize the data.
EVS utilizes expert systems to analyze the input data, construct a multidimensional variogram which is a best fit to the dataset being analyzed, and then perform kriging in the domain to be considered in the visualization. The user is provided the option to specify values for parameters which control the variogram\kriging procedure, and the subsequent display and analysis of the data. One of the fundamental design criteria used in developing EVS's variogram and kriging algorithms was to produce kriged distributions that honor the measured distributions as closely as possible, and to provide the user with a valid mechanism to compare the modeled and measured domains. EVS’s data posting and surfacing capabilities allow the user to make these comparisons with a minimum amount of effort. This section provides a description of the algorithms used in the variogram computation and kriging modules in EVS, along with general guidelines for setting parameter values for the variogram and kriging procedures.
EVS employs an expert system variogram analysis procedure that examines the spatial distribution and number of points in the input data set, and calculates a variogram that is a best fit to the data under the constraints imposed upon it by the user. In all of EVS's variogram algorithms, if a parameter has a default value of 0 and the user does not change it, then no constraints are being placed on the procedure and the algorithm will calculate, use, and return those parameters which provide the best fit of the variogram to the data. For many data sets, the unconstrained analyses will provide a good first cut model of the data, which might be improved by placing some constraints on the procedure. However, in many cases the scientist has additional knowledge of the data which should be appropriately considered in the variogram modeling procedure by constraining certain input parameters. Discussions of the significance of each of the general variogram parameters, and some guidelines that can be used in setting their values, is provided in the following module sections, and in the help pages of each of the kriging modules.
Most of EVS's kriging modules allow the user to specify the variogram pair search range, variogram range, and minimum range. EVS's variogram modules utilize a nugget of zero, which cannot be changed, and which basically require the calculated value to be equal to the known value of data points that fall exactly on a grid point in the modeled domain. For most environmental applications, this restriction of the nugget provides much more representative results than allowing the nugget to be greater than zero, and thus allowing estimated data points to be different than the measured data points when they coincide. For some specialized applications however, the user may want to consider a finite nugget, and in these cases EVS can not be used as it is currently implemented.
EVS’s capabilities to grid and interpolate sparse measured data in three dimensions are unparalleled. EVS performs all interpolation using an accurate and geostatistically defensible process called Kriging. Kriging is a mathematical process recognized by the EPA as the best and standard means for interpolation and extrapolation of measured data. EVS provides a user-friendly expert system to drive its Kriging modules lifting the burden of determining optimal variogram parameters from the user. With EVS, the user can rely on expert system calculated default values to provide quality answers in minimal time.
Kriging is the only data estimation method which also provides statistical measures of goodness. EVS provides statistical confidence and uncertainty with all estimated parameters. These additional statistical measures are extremely useful in guiding additional site investigation. Our experience is that by using maximum uncertainty to guide site investigations, a 30% reduction in sampling locations can be realized for an equivalent quality of assessment.
As a user defined alternative to confidence and uncertainty, EVS will provide statistical bounds on the parameter estimate (This feature available only in EVS-PRO& EVS). In other words, EVS will determine the nominal, minimum, and maximum estimated distribution based on a user specified confidence level. With EVS, you can now directly answer the question: With my limited measured data, to an 80% confidence level, what is the largest and smallest plume I can expect?
EVS’s Kriging modules utilize a highly efficient algorithm which provides very fast and robust, interpolation and extrapolation of measured data sets. The employment of highly optimized matrix solution methods provides the capabilities to krige very large data sets quickly and easily.
EVS provides a full spectrum of three-dimensional gridding options, including: rectilinear grids with uniform spacing in x, y, & z directions; rectilinear grids with uniform spacing in x & y directions with z spacing determined by geologic layers; finite difference type grids with variable spacing in x & y directions and z spacing determined by geologic layers; convex hull bounded gridding with z spacing determined by geologic layers; and adaptive gridding which automatically refines gridding in the cell(s) surrounding measured samples to ensure that the interpolated results and isosurfaces accurately honor measured sample data. Adaptive gridding provides an effective resolution that cannot be approximated by any other method. It often provides more accurate results than increasing the number of elements by 100 to 1000 times.
EVS provides a rich library of data filtering and subsetting modules. The options include filtering the data based on volumetric subsetting of the data range, performing mathematical manipulation of multiple data fields, and slicing, cutting, and presenting isolines on all or the subsetted regions of the data.
EVS quickly and easily extracts surface and volumetric subsets of the Kriged (gridded) data. EVS’s modular structure allows the user to perform multiple, serial, subsetting operations using any of a number of nodal data parameters. For example, this functionality provides a mechanism to determine the volumetric subset which is those regions of the domain where cesium concentrations are above 50 pCi/g, soil porosity is above 12%, elevations range from 530 to 595 feet, and the statistical confidence in the cesium concentration is above 60%.
EVS provides the ability to include any number of arbitrarily placed and oriented slice and cutting planes within the three-dimensional Kriged data domain. Planes are positioned by the user by controlling rotations (about three axes) and position (distance of plane from the domain centroid).
EVS’s three dimensional viewer allows the user to perform real time rotations and manipulations on the image displayed in the viewer. Selection and manipulation of the color and material properties which control the rendering of individual objects is also allowed
EVS can display an unlimited number of objects simultaneously. All objects are truly three-dimensional and objects to be displayed together must be in the same coordinate system. EVS has the ability to display boreholes colored according to measured concentration, or to display boreholes whose color alternates according to a user defined depth interval and to display the measured data samples as sized and colored spheres. Spheres and boreholes can also be exploded by geologic layer when geology information is also available.
EVS provides complete interactive control over viewing perspective, azimuth, elevation, scale and background color. Numerous other viewing parameters can also be controlled such as object rendering method (shading, outlining, etc.), object transparency, lighting (number and color and type of lights), background color, and more. Isosurface level is user controllable (and can be animated), and plots can be labeled within EVS or bitmap images can be exported to other applications.
Because EVS runs under all versions of Microsoft Windows operating systems, there are numerous options for printing output. EVS renders each scene in a user defined resolution. The Viewer window may be "captured" to the clipboard and pasted into another application. EVS allows printing directly from the program at a user specified resolution. EVS also includes an Output_Images module which will create images in many image formats, including Windows Bitmap (.bmp) files, Portable Network Graphic (.png) files, and many other compressed and uncompressed formats. All bitmap images can be imported into other applications such as CorelDrawTM, or Adobe Illustrator TM to add additional annotation and to print.
EVS also provides the ability to output any object (isosurfaces, labeled isolines, axes, etc.) in industry standard files, including DXF and Shapefiles. This output format provides a vector (versus raster) definition of each object. This provides the ability to integrate EVS output with CAD drawings or to plot objects in large scale (e.g. poster size) with vector resolution, or to bring output into GIS programs.
In addition to printing, EVS provides easy to use, powerful capabilities to create animation sequences. These animations can be produced as Windows Audio-Visual Interleaved (.avi) data files and (with special hardware) written directly to NTSC or PAL video formats such as DVD. The ability to produce animations showing rotation of 3D objects, or variations in subsetting level provides an invaluable capability that printed graphics cannot equal.
EVS also provides the ability to create C Tech’s 4DIM files, which are fully interactive 3D animations. These can be viewed with the Playback_4DIM module in EVS, or with a standalone 4DIM player.
Because EVS provides a mechanism to save, and subsequently load, networks of modules (as a custom application), and also has a powerful scripting (macro) language, the process of generating initial figures can be fully automated. Because of EVS’s expert system driven Kriging, no user intervention is required to produce reasonable results.
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