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3.1 The display system
For precise measurement and operator comfort the following
parameters should be looked at during the selection phase
of the monitor(s) (see Ref. 1):
- Good brightness
- High picture clarity and contrast
- Defocussing convergence
- Flicker
- Reflection glare
- Pixel non-linearity
An adequate monitor should be flickerfree, non-interlaced
and have a refresh rate of more than 60 Hz. Examples
can be found, like the SUN bitmapped display (1150» 900
pixel), the AZURAY 2000/BW (2048*2048 pixel) or the
HITACHI HM-6219 (2730*2048 pixel), to name just a
few. High resolution is desireable to have a wide field of
view (FOV). An image digitized with 12.5 micron on a
1024*1024 display gives only a FOV of 12.8x12.8 mm
compared to standard 3x3 cm on photogrammetric instru
ments. For stereo display, only three methods are currently
considered to be working operational, namely the anaglyphic
method, the use of stereoscopes (KERN, CONTEXT MAPPER)
and the active and passive polarization techniques (TOPCON,
MATRA T10N, MACDONALD DETTWILER, MOMS II, DMS).
In order to be comparable to analog/analytical photogram
metric instruments a sub-pixel measurement accuracy and
method should be available, which can be achieved either
by zooming the image or performing an on-line resampling
of the image data. The latter one implies a high processor
performance wich will be addressed in chapter 3.3.
3.2 Memory and Data Transfer Rates
In order to have as few disc I/O as possible the image
RAM memory should be as large as possible. Standard
boards of 2 Mbyte (equivalent to 8*512*512*8bit) are
only a poor solution. Working with high resolution satellite
images or digitized photographs will cause the system to
be heavily engaged in reloading images to the RAM memory,
while the operator roams over the entire image. This
