Generating color terrain images in an emergency response system Page: 4 of 17
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of 63.5 meters. Next., software was produced by ARAC computer scientists to access,
transform, and average the DMA data onto grids that were appropriate for ARAC’s use
|5]. In addition, a smaller (109 Megabyte), coarser resolution (500 it) data base was
created. During an accident response, a regional terrain file is generated from this smaller
data base which typically covers a 200 km square area centered on the release point. Having
installed the data base system on the LLNL central computer system, ARAC scientists
then moved it to the ARAC computing facility. By late 1984, the system was operational
on ARAC’s VAX 782’s, and it then became possible to generate a regional terrain file
centered at any point in the contiguous I'.S. within 3 minutes.
Concurrent with the effort to develop the terrain data base and its attending programs,
work was being done to develop software for creating and displaying realistic images of
the terrain data. It was clear from the Titan II accident that contour maps are notably
weak in the area of human perception (Fig. 1). This is especially true in the case of
complex terrain, where contours tend to crowd each other, and hills and valleys become
indistinguishable. Wire frame plots and block representations have similar shortcomings
(Figs. 2-3). It was decided to investigate the feasibility of creating color shaded raster
images, and in 1982 software was created on LLNL’s CRAY-1 computers to generate
terrain views for the simplest case, that is with the observer directly above the center of
the terrain grid looking down, i.e., an overhead view. However, for an assessor to visualize
the topography of a given area, it would be helpful to view the area from any arbitrary
vantage point. Introducing this generalization increases the complexity of the calculation
by an order of magnitude, since one can no longer make the simplifying assumption that
all points on the terrain surface are visible to the observer, as can be done in the overhead
case. In calculating arbitrary perspective views, the complication of hidden surfaces is
introduced, thus increasing the calculational time significantly. By the end of 1983, the
more general perspective program had been completed and was capable of calculating a
terrain image in approximately one minute on the CRAY-1 ,
Generation of high-quality images in real time had been successfully demonstrated on
LLNL’s CRAY-l’s. However, two aspects of this prototype system excluded it from being
useable in an operational sense. First, the software which created the image data resided
on the LLNL central computing facility, with a timesharing operating system whose users,
of which ARAC scientists comprise a small segment, compete for access. The software
was ultimately required to run on ARAC’s dedicated VAX-based computer system. The
projected time for creation of a terrain image on ARAC’s VAX computers was 10-15
minutes, clearly an unacceptable timeframe for emergency response, especially when the
need for creating many different images clearly exists. The second aspect to be addressed
was the actual displaying of the images in real time. Each element in the color image data
consists of three integers in the range 0-255 representing the intensities of the red, green,
and blue components at each point in the image, thus allowing a range of over 15 million
composite colors. Barring the procurement, of some prohibitively expensive, hardware to
display its images, ARAC would have to rely on LLNL’s Dicomed film recorder which
produces 35mm slides from digital data in a turn-around time of a day or more.
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Belles, R.D. Generating color terrain images in an emergency response system, article, August 1, 1985; [Livermore,] California. (digital.library.unt.edu/ark:/67531/metadc1066640/m1/4/: accessed February 18, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.