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pre-existing or can be generated simultancously. These
corrected orthophoto patches are stored on disk. The system
works one patch at a time until the whole model area is
covered.
Figl ADAM Technology PROMAP System
For DEM generation, images are captured from both left and
right CCD cameras. Image correlation software determines
matching points and generates height measurements using the
model orientation parameters. It generates DEMs quickly,
with minimal user input. The operator has the ability to check
the correlated points in stereo using an anaglyph display (using
red/blue glasses), on a basic stereo monitor (mirror stereoscope
based) or a digital 3D display. The DEM can also be checked
via drive-back in the stereoplotter itself. The DEM is stored on
hard disk and can also be used immediately for simultaneous
Orthophoto generation.
Left CCD Right CCD E
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PROMAP ‘System ^.
E Framegrabber
Fig2 . CCD cameras in PROMAP System
Advantages of this technique
* The ADAM Orthophoto generation only stores the final
orthophoto, thereby reducing the hard disk storage
requirements by up to 75% of that required by standard
soft photogrammetric systems. Whereas a soft
photogrammetric system reads the digital image data from
disk or memory, the ADAM PROMAP Automatic DEM
and Orthophoto Generator commands the machine to go to
the desired location and acquire the data via CCD camera
and frame-grabber when it is required. This eliminates the
need to scan and store the whole of every photograph for
the job. Including stereo overlaps and sidelaps in a
photogrammetric block, each ground point is covered
approximately 2.7 times in a softcopy system. This is in
addition to the disk space which is needed to store any
intermediate files generated by the system and, of course,
the final orthophoto.
e No Scanner is required. The images are scanned patch by
patch in the PROMAP System simultaneously with the
Automatic DEM and Orthophoto generation.
* The ADAM PROMAP system is still a fully functional
analytical stereoplotter, even when the Automatic DEM
and Orthophoto Generation functions are installed.
757
Therefore, if required, the PROMAP operator can digitise
fine detail which would not be visible on photographs
scanned for a soft photogrammetric system.
* The ADAM PROMAP system is PC based and uses
Microsoft Windows. This makes it easier to learn and use,
and considerably less expensive than the Unix based
workstations which are generally required for full format
soft photogrammetric systems.
e The ADAM PROMAP system offers users of conventional
analytical stereoplotters a simple low-cost entry path into
the new digital orthophoto and digital photogrammetric
field.
File sizes
The following table shows the amount of disk space required
even for a small block. The resolution of the orthophoto is
assumed to be 15 microns, same as the scanned pixel size.
Monochrome| Colour
1 diapositive @ 15 microns 224Mb 672Mb
Block of 3 strips x 8 models/strip| 6,048Mb 18,144Mb
Orthophotos covering the block 1,830Mb 5,489Mb
Table 1 Sizes of image files in megabytes (uncompressed)
System components
Hardware:
e The system uses off-the-shelf monochrome CCD cameras.
* Ahigh speed frame-grabber running on the Pentium’s PCI
bus is used.
e The lens system of the CCD cameras is fixed. Focusing
and alignment are done by an ADAM technician. The
resulting pixel size is 15 microns on the diapositive. The
Orthophoto can be generated to any required ground pixel
size by re-sampling the scanned pixels. Some commonly
used Ink jet plotters operate at resolutions of 300dpi (85
microns) in colour. Printing one pixel scanned at 15
microns as one 300 dpi dot results in a nominal scale of
5.6 between orthophoto and diapositive.
e The system runs on a relatively inexpensive Pentium PC
under Windows NT. A Windows 95 version of the
product is also planned.
e The images required for colour orthophotos are created
from the monochrome images acquired by camera and
frame-grabber by mechanically switching red, green and
blue filters. These filters are placed in front of the
stereoplotter’s plate illumination system. Three frames,
one for each filter are grabbed and the colour images are
formed by combining them.
Software:
* The software includes a calibration routine for the CCD
camera, lens and frame-grabber to compensate for
geometric and radiometric errors of the lens/CCD/frame-
grabber system. The geometric calibration requires the
operator to measure a number of points on the
stereoplotter from which the calibration parameters are
calculated.
e The radiometric calibrations does not require any user
interaction. A lookup table is then used for the correction
of radiometric distortions.
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996
