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From this study, certain facts emerge: 
(1) Whereas conventional TV has an optical viewing distance of 7H (H = 
screen height), a 940 interlaced system allows a viewing distance of 
4H. 
(2) If the scanning is non interlaced, 965 lines will support a viewing 
distance of only 2.5H. 
(3) A field frequency of 45 Hz is sufficient to give smoothness up to 
the highest tracking speed of the human visual system, 20?/s. 
The HDTV system is said to have a subjective quality comparable to that 
of a 35 mm slide and superior to that of a 35 mm motion picture film; and 
can also transfer an 8''x11" page of 10.5 point characters (2.6 mm x 2.6 mm). 
This system is clearly more desirable than standard TV to replace the optics 
on conventional stereo photogrammetric instruments. Meanwhile, standard TV 
can be improved upon by using frame memories and a noninterlaced display of 
1000 lines, Weber, 1985. A TV based image transfer system is more than a 
substitute for an optical transfer system; it opens wide possibilities. 
This concept allows portable instrument design of unconstrained physical 
geometry, Real, 1979, capable of capturing and processing dynamic 3-D scenes 
for in-situ, filmless analysis, measurement, manipulation, storage and 
control. 
3.1 Conversion; Video Memory 
Flash video analog to digital converters to 13 bits resolution (and to 
200 MHz for 8 bits) and low cost, high speed megapixel dynamic random access 
frame memories are essential components in electronic imaging systems. When 
preserving image fidelity is paramount, as it is in visual communications 
(which includes photogrammetric instruments used by a human operator), there 
are arguments for digitizing the photometric information to more than 8 
bits, Frost, 1977, and having 12 bit wide video memory to permit digital 
integration of low level data, Mengers, 1978. Since the least significant 
bit of A/D conversion can almost be regarded as a noise bit, even 8 bit-wide 
image data should be derived from 9 bit conversion. 
The impact that electronic imaging and processing components have on the 
inherent accuracy of a digitized image is important. Because studies on 
this matter are incomplete, solid state camera calibration and error sources 
in the digital image are subjects of concern at NRC, Havelock, 1984. 
3.2 Image Display 
There is no solid state substitute now for the electron beam CRT for high 
resolution image display. State of the art in military solid state display 
development is 10" 512x660 pixel black and white, 4" 320x240 color, Naegel, 
1986. The analog nature of electron beam addressing in the CRT display may 
compromise displayed metric fidelity. However, as is known from a history 
of measurement experience on analytical plotters, some geometric distortion 
is acceptable in the stereo viewing system provided the measuring marks are 
properly positioned with respect to the images seen by the human operator. 
It is known from experiments at NRC that once the marks are properly 
aligned, relatively accurate measurement is possible, even from stereo TV 
images which look significantly inferior to their optical counterpart. 
CRT monochrome displays exist to 4000x4000 pixels and color to 2000x2000 
pixels, Michaels, 1986. However, this latter device (Sony) is expensive 
89