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Digital Mapping Techniques '00 -- Workshop Proceedings
U.S. Geological Survey Open-File Report 00-325

What Visualization Contributes to Digital Mapping

By Paul J. Morin

Department of Geology and Geophysics
University of Minnesota
310 Pillsbury Drive
Minneapolis, MN 55455
Telephone: (612) 626-0505
Fax: (612) 625-3819


Scientific Visualization, the artistic expression of scientific data, has much to contribute to Digital Mapping, the creation of maps with computers. Both have many of the same goals including the understanding of data, and the creation of educational and reference materials. The key difference is the divergent paths the fields have taken to get where they are today. Digital mapping has been far more successful in being used as a day-to-day tool and providing a core set of tools and technologies. Three spatial dimensions and change over time are probably the two most important factors that Scientific Visualization has to offer the field of digital mapping. In addition, scientific visualization has embraced virtual reality, and is finally becoming available to its users through low cost, high performance, hardware.


screenshot of mantle convection simulation

Figure 1. A screenshot of a mantle convection simulation using BOB.

Modern visualization arose from the computational scientist's need to visualize the large simulations produced by the supercomputers of the period. This need has led to the assumption that all scientific data is in three-dimensions and is time dependent, sometimes to the exclusion of 2D visualization. An example of three dimensional visualization software is the program Brick of Bytes (BOB) by Ken Chin-Purcell. This application written for Silicon Graphics, Inc. (SGI) workstations reads 3D raster files and quickly displays data without re-rendering surfaces. Each volume element (voxel) is assigned a color and degree of opacity. The data is drawn beginning with the voxels farthest from the viewer's eye and ending with those that are closest. The result is an image with a cloud like appearance.

The primary issue that BOB addressed was large 3D datasets, as shown in figure 1. Many of the animations that used BOB had several thousand timesteps that were individually larger than 512x512x512 bytes with total a total size of over 100 gigabytes. BOB's advantage was that it was written as a simple turnkey program that gave users access to their data in minutes. Though BOB was written nearly 10 years ago many variants of it are still being used.


A hierarchy of graphics standards strongly influences and benefits Scientific Visualization and 3D graphics in general. Open GL (OGL) was developed by Silicon Graphics, Inc. and is the primary programming interface used for creating visualizations embedded in applications. Nearly all visualization software uses some form of the OGL language to implement their 3D graphics. It provides a platform-independent Application Programming Interface (API) for creating 3D graphics on a large number of workstations and personal computers.

With recent graphics hardware advances, modern scientific visualization is being driven to the desktop and into the hands of more users. What once required a mid-range graphics workstation can now be performed on a consumer grade Windows PC. The primary factor we have to thank for this drop in price is the computer game industry and most notably the first-person shoot-em-up games, such as Doom.

Table 1 contains a comparison of three very different graphics platforms. The Onyx 2 is the computer of choice for high-end visualization and virtual reality. It is available in a desk side version that is about half the size of a desk or in a format the size and shape of a refrigerator. The PC is a standard Intel/Windows computer with a high-end consumer graphics board. The Sony Playstation 2 is the newest generation of home video game computers.

Table 1. Comparison of three types of computers with powerful graphics subsystems.

  SGI Onyx 2 with Infinite Reality Graphics High end PC with a Asus 6800 Graphics Card Sony Playstation 2
CPU 250 MHz + 1 GHz 300 MHz
RAM Up to 16 gigabytes Gigabyte + 32 MB
Max Polygon Rate 10 Million per pipeline/sec 7 Million/sec 20 Million/sec
Stereo Images Yes Yes No
Communication Any Any PCMCIA Card
Weight 400 lbs. 20 lbs. Under 5 lbs.
Cost $50,000-Million+ Less than $4000 $300-$400

A few items in Table 1 are worth noting. Even though the Onyx 2 has CPU clock speeds that are well below those manufactured by Intel, they are still faster in floating point calculations because they are primarily designed for use in science and engineering. The Sony Playstation 2 and the Windows PC have significantly smaller memory capacity and, more importantly, the speed that the CPU can access the memory is more than an order of magnitude slower than the Onyx 2.

Probably the most interesting benchmark is the maximum polygon rate of each of the graphics subsystems. This is a relatively new development for the increasingly low-cost systems to rival the performance of high-end systems. The maximum polygon rate is a significant measure, as polygons comprise almost every object observed within a 3D scene. If more polygons are pushed to the screen, objects can be more elaborate and responsive when being manipulated by a user. Moreover, these statistics are for texture mapped polygons. That is, polygons that have been painted with a raster image. The ramifications of texture mapping for practitioners of digital mapping is very important. It is the simplest way to texture map a DEM with any geo-referenced raster data.

It is worth noting that the Macintosh series of computers are rarely used in 3D scientific visualization. The primary reason is that, until recently, Apple has not opened the Macintosh platform to third party graphics boards that support 3D graphics standards, such as OGL.


There are three highly flexible 3D visualization packages currently available; Advanced Visualization System (AVS) and Iris Explorer are commercial, whereas Open Data Explorer is now free and has been placed in open source by IBM. Figure 2 shows Explorer used for digital mapping. These programs provide the most generic frameworks for data manipulation, data import, and the customization of existing features by a programmer through a common programming interface, but they are not customized for a given science. In other words, these packages are not plug and play.

remote sensing image painted on a DEM Figure 2. A remote sensing image painted on a DEM using Iris Explorer on Windows NT. Note the modules in the flowchart-like interface.

All three visualization packages are used in a very similar way. Users create a flow chart within a sophisticated graphical user interface, consisting of modules connected by paths that direct the flow of data. This "data flow" model for constructing visualizations is very quick and powerful, but it has one primary drawback. It makes many copies of data and requires a large amount of RAM and hard disk space to run. It is common to have hundreds of megabytes of RAM on any machine running these programs. The advantage of using this data flow model is that modules can be quickly rearranged, added, written, and adapted without knowing the entire system.

Why Isn't There More Software?
Economic factors are the primary reason for the shortage of visualization software on the market. Many of the currently available commercial applications were developed on graphics workstations that cost a minimum of $10,000 and sometimes exceeded $100,000. Users found easy justification for software costing more that $10,000 when it compared favorably to the original price of the computer. But when the same software is available on a Windows or Linux PC, the pricing structure is turned on its head. How many of us can justify a $10,000 application on a $2000 computer? Now that this shift to lower priced, high performance computers is in progress, the best we can do is use the available tools and wait for the market to adjust to the new realities.


Over the past decade, the large amount of data available in 3D, time dependent data sets was the primary problem in scientific visualization. As datasets increase in size it becomes an increasing challenge to manage, display and interpret. One approach has been to put a user within a synthetic environment, or virtual reality (VR), to trick the senses into interpreting data as they would the real world. Perhaps the most dramatic, immersive VR technology is the CAVE developed in the Electronic Visualization Lab at the University of Illinois, Chicago and Champaign-Urbana.

A CAVE consists of a large graphics workstation, which displays stereo images in a 10'x10'x10' room with up to four walls, the floor, and ceiling (Fig. 3). A small number of users (usually under 3) can walk within the objects being displayed, giving a sense of immersion.

User in a CAVE

Figure 3a. A user in a CAVE (figure courtesy Fakespace Systems, Inc.).

Schematic of the exterior of a four walled CAVE

Figure 3b. A schematic of the exterior of a four walled CAVE (figure courtesy Fakespace Systems, Inc.).

Artist¹'s conception of a WorkWall Figure 4. An artist's conception of a WorkWall (figure courtesy Fakespace Systems, Inc.)

CAVEs are expensive. A full 6-sided CAVE with a powerful SGI workstation can exceed one million dollars including the projectors, computer, screen, and software. Interestingly, the barrier to lowering the cost of this technology is not the cost of the computers, but the cost of the projectors. The most inexpensive projector that supports stereo images is $20,000. Also, the usefulness of a multi-wall CAVE is limited to a small number of people that can crowd around the user with the position sensor on his stereo goggles. An alternative is a single wall CAVE, also called a WorkWall (Fig. 4). This configuration uses less expensive hardware and gives a larger group of people more of a shared experience. WorkWalls are finding their way into design labs and classrooms for just this reason.

Another lower cost alternative is to use one of the new breed of stereo boards designed for the Advanced Graphics Interface (AGI) slot in a Windows PC. Boards such as the Asus 6800 and Elsa Erazor X cost less than $350 with stereo goggles. The Geology and Geophysics Department of the University of Minnesota is exploring installing these graphics boards in every PC in the physical geology lab rooms. Students will add the exploration of earthquake hypocenters and topography in 3D to traditional labs on mineral identification and map reading.


Perhaps the most powerful way to use Scientific Visualization is over the Internet, without specialized software, through a browser. The Space Physics and Aeronomy Research Collaboratory (SPARC) is a good example. SPARC is a framework for collaboration that presently has over 150 feeds from data sources as diverse as satellites, ground based radars, and models. Visualizations are produced automatically and in near real time as data arrive and are automatically pushed to the user's browser (Fig. 5).

SPARC opening page

Figure 5. The SPARC opening page. Any of the pages can be customized to show
any one of numerous data sources.

VRML file of earthquake hypocenters beneath Tonga

Figure 6. A VRML file of earthquake hypocenters beneath Tonga.

The next generation of Internet delivery of visualization currently under development will allow users to construct visualizations from scratch using data sources distributed around the Internet and delivered as GIF images, QuickTime movies, and Virtual Reality Markup Language (VRML) objects (Fig. 6) using the CosmoPlayer plugin by Computer Associates International or the 3SpaceAssistant application and plugin from Template Graphics Software, Inc. The aim is to remove most, if not all, of the visualization software from the user's computer and to produce visualizations from data anywhere on the Internet. This frees the user from installing large numbers of plug-ins or downloading large JAVA applets that don't work. It also keeps the complex visualization software at a central site where it can be maintained and updated easily. The SPARC system could be applied to the real time display of stream flow data. As data is downloaded from data loggers in the field, visualizations could be created and pushed to a display that has been custom described by the user. A second possible application takes advantage of SPARC's infrastructure for historical databases. Paleoclimate data can be included in SPARC along with their metadata, allowing users to construct maps in any area of the world, using a number of available proxies or models.


The current state of mainstream scientific visualization software falls short of being an ideal tool for use in digital mapping. Though polygons are drawn quickly and the images are impressive, the tools are lacking to create objects from standard earth science and Geographic Information System (GIS) formats in a way that geologists intuitively understand. The fallback position includes common GIS and remote sensing software in combination with existing visualization packages. This is a situation common in many sciences. Visualization beyond two dimensions hasn't caught on as a day to day tool. The lack of agreement on Macintosh/Wintel graphics standards, the software industry's switch from workstation to PC economics, and little artistic training in the earth sciences can all be blamed. Even on the high end of the visualization food chain the software tools are painstakingly handcrafted and not readily customized for various scientific disciplines. Choose tools carefully and be seduced by the increased understanding that you extract from your data, not the pretty pictures. Just because you can spin your field area in three-dimensions doesn't mean that you understand more of what's going on.


CAVE References
The Electronic Visualization Laboratory --

CAVE Guide --

Fakespace Systems Inc. -- 809 Wellington St., N., Kitchener, ON, Canada, N2G 4J6, (519) 749-3339,

3D on the Web
Web3D Consortium --

CosmoPlayer -- Computer Associates International, Inc., One Computer Associates Plaza, Islandia, NY 11749, (631) 342-5224,

3SpaceAssistant -- Template Graphics Software, Inc.,

Space Physics and Aeronomy Research Collaboratory (SPARC) --

Brick of Bytes (BOB) --

Generic Scientific Visualization Packages
Iris Explorer -- NAG LTD, Wilkinson House, Jordan Hill Road, OXFORD, OX2 8DR, UK, +44 1865 511245,

Advanced Visual Systems,Inc., 300 Fifth Avenue, Waltham, MA 02451, 781-890-4300,

IBM Open Data Explorer --

Stereo Hardware and Software --

Silicon Graphics, Inc., 1600 Amphitheatre Parkway, Mountain View, CA 94043, (650) 960-1980,

Asus, Inc., 150 Li-Te Road, Peitou, Taipei, Taiwan 112 R.O.C., +886-2-2894-3447,

Elsa Erazor X -- Elsa, Inc., 1630 Zanker Rd., San Jose, CA 95112, (408) 961-4600,

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U.S.Department of the Interior, U.S. Geological Survey
Maintained by Dave Soller
Last updated 11.01.00