is 1320 H x 1035 V pixels and measures 8.98mm H x 
7.04mm V. These pixels are 6.8 um square and are 
evenly spaced horizontally and vertically. Video infor- 
mation is digitized to 256 grey levels by the camera's 
built in A/D converter. A full frame of video information 
is 1.3Mbytes in size and is transferred in 144.5 ms. 
Output video is in both analog and digital format. 
Digital data is sent as an EIA compatible 8 bit parallel 
signal . The analog output is a non-composite, 1volt 
peak-peak signal transmittable on a 70 ohm impedance 
line. 
The lens used is a variable focus 20mm Nikon with a 
field of view approximately 20 by 25 degrees. The 
aperture is set manually with a range of f2.8 to f22. The 
  
  
Figure 1 
Videk Shown in CRC-1 Roll Ring 
  
  
  
shutter is an electronically actuated mechanical blade 
with variable exposure timing (1/100 sec to 1/4 sec or 
longer in certain circumstances). Roll capability was 
added via a modified CRC-1 roll ring (see Figure 1) 
The image processing boards used are the Imagraph 
HI*DEF system. The system consists of three boards: A 
High Definition Frame Buffer (HDFB), a High Defini- 
tion Frame Grabber (HDFG) and an Analog Processing 
Module (APM). The system also includes the HI*DEF 
software library. These routines provide the basic soft- 
ware interface to the HI*DEF boards. 
The HDFB is a high resolution graphics controller and 
frame buffer that displays images in 8 bit planes (256 
shades). Images are displayed at a resolution of 1280 H 
by 1024 V. Also provided are 2 bit planes of overlay 
memory that can be displayed at / resolution (320 H by 
1024 V). Videooutput is RS-343 RGB at a 60 Hz refresh 
rate. 
The HDFG is a digital frame grabber that can handle 
8 or 12 bits of TTL digital video input. The frame 
grabber has 1.28 Mbytes of frame buffer memory. It 
also has 6K of input LUT memory. 
The APM is a daughter board to the HDFG and can 
handle a variety of analog video signals. Analog input 
is digitized to 256 grey levels. The digital information 
can then be processed by the HDFG. 
The HI*DEF software library consists of hardware 
device drivers and image processing utilities specific to 
the Imagragh boards. The libraries are written and 
designed for use with MicroSoft C, version 5.1. 
The HI*DEF boards are installed in a DELL 486D/33 
80486 based computer running at 33 MHz. The 
operating system is MS-DOS 5.0 with application code 
written in MicroSoft C. Video is displayed on an 18" 
RGB monitor manufactured by Monitronix Corp. 
3. TEST NETWORKS 
The studies discussed in this paper center around 
results from the measurements of three test fields, as 
discussed in the introduction. Several aspects of the test 
are common and are discussed here. 
Targets on the test fields were high contrast images with 
virtually no competing noise and occupied from 50 to 
150 pixels on the sensor. Targets were centroided using 
a weighted center of mass technique suggested by 
Trinder (1989): 
n m 
= ja 
X 1 2,27) Ey Wi 
| Su. 
VS (1) 
i=l j=1 
n m 
M=Y 3 aw, 
izi zl 
2 is either 1 or 0; 1 if pixel, is above threshold value. 
w, is weight value equal to the light intensity of the pixel 
i is the row position of the pixel 
j is the column position of the pixel 
All of the fields were calibrated using the GSI STARS 
photogrammetric system; in particular the CRC-2 
camera, the AutoSet-2 film comparator and the STARS 
suite of programs centered around a rigorous self- 
calibration bundle adjustment program. Typically, this 
calibration was more than 5 times more accurate than 
the video-based work. 
All simulations were completed using the STARS 
    
  
    
    
  
  
  
  
  
  
  
  
  
  
    
    
   
   
  
   
   
   
    
   
  
  
  
  
  
  
   
    
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