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map or performing image reprojection. All map 
projections included in USGS's standard coordinate 
transformation software, the General Cartographic 
Transformation Package, would have to be supported. 
The image processing functions specified for the 
system were: 
-Image zoom 
-Image rotation 
-Image pan 
-Image compression/decompression 
-High- and low-pass filters and edge- 
sharpening algorithms 
-Gray-scale remapping, with both interactive 
and automatic default adjustments and 
pseudocoloring. 
-Image flicker or wipe 
-Fading of image intensity independent of the 
intensity of any superimposed graphics. 
-Arithmetic and logical functions, including 
the capability to perform basic mathematical 
operations on a single image or on multiple 
images, to combine virtual memory planes, 
and to create a percentage mixture of two 
virtual-memory planes. 
The basic multispectral processing capabilities would 
include: 
-Manipulating bands by color plane. 
-Selecting band combinations to allow display 
of up to seven spectral bands and five 
additional derived bands all logically linked 
and managed as a single image. 
-Mapping any spectral band to any of the 
three primary colors. 
-Performing both supervised and unsupervised 
image classifications. Image classification 
functions would provide for statistical output 
and for postclassification smoothing and 
filtering of the image. 
A GIS would have to be provided as part of the 
System. It would need to possess both raster and 
vector capabilities and to be fully integrated with the 
System's image processing capabilities. Further, it 
would be important for the operators to be able to use 
the GIS in conjunction with the displayed images 
Without having to transfer from window to window. In 
other words a common user interface was desired. 
The GIS would need to permit the display of vector- 
based GIS information, in graphics form, 
Superimposable over both monoscopic and 
stereoscopic images The graphic presentation would 
have to be in stereo whenever the necessary elevation 
275 
data were available, and when not available, it would 
have to be displayed at the median elevation of the 
model. 
Although it was hoped that the system would be able 
to exercise the full-function set of vector GIS 
capabilities while viewing and manipulating an imagery 
model in stereo, at the very minimum the system 
should allow the user to select features for display by 
attribute, to digitize, edit, and save information in the 
GIS data base, and to query the GIS data base for 
attribute information, all while maintaining full image 
processing capabilities. 
The GIS would also need raster processing capabilities 
to permit conversion between raster and vector data 
sets, Boolean operations within raster data sets, and 
display of raster data sets in conjunction with 
registered images, with flicker, wipe, and split-screen 
image processing capabilities present. 
The system also must be capable of maintaining raster 
maps, orthophoto images, and near-orthophoto or 
nearly rectified images so that they could be readily 
displayed in answer to a geographic query. 
The GIS would need the capability of incorporating 
new or revised functions. 
The system would need enough mass storage capacity 
to permit storage of adequate data for analysis and to 
permit retrieval of that data in a timely manner. 
Although GIS and imagery data would not need to be 
integrated into the same storage scheme, they would 
have to be addressable in a similar manner. 
Finallythere would have to be an index accessible 
through the GIS that would index all system images, 
both those online and those in temporary storage. 
THE NARSAP SYSTEM 
The system purchased by the USGS was integrated by 
Autometric, Inc, of Alexandria, Virginia. All 
components are COTS items. The system consists of 
Silicon Graphics, Inc., (SGI) hardware, with ERDAS 
Imagine image processing software, including the 
Spatial Modeler, Vector Module, Image Catalog, 
Toolkit, OrthoMAX, and ARC/INFO GIS. The exact 
hardware configuration of the system as delivered 
consists of: 
The system server, an SGI Challenge L with 
dual CPU's, 128 Mb of memory, a 1.2-GB 
system disk, 24 Gb of shared disk space, an 
8mm tape drive, and a CD-ROM drive. 
Five SGI Indigo Elan workstations, each with 
96 Mb of memory, a 1-Gb system disk, 2-Gb