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Title
Systems for data processing, anaylsis and representation


generated using different Ground Sampling
Distance (GSD).
Manual DTM GSD = 28 ft.
Automatic DTM GSD = 25 ft.
No. of DTM points Compared: 744
Average Error Calculated: -0.08 ft.
Standard Deviation: 1.68 ft.
Manual DTM GSD = 25 ft.
Automatic DTM GSD = 12.5 ft.
then interpolated to 25ft.
No. of DTM points Compared: 744
Average Error Calculated: -0.035 ft.
Standard Deviation: 1.28 ft.
There are two conditions under which the above
accuracies were obtained. First, ground controls
were minimal in all above models, and second,
images were scanned at a 22.5 micron resolution.
With photo scale at 1"=300’, one pixel is 0.25 ft
on ground. Scanning with 12.5 micron resolution
would have yielded 0.15 ft on ground, a
significant difference.
3.4 Speed
An average of twenty percent of all models seems
to be covered by elevated vegetation. Manual
editing or manual extraction would be needed to
obtain correct elevations of ground surface. This
task is performed within the manual
extraction/editing option available in most softcopy
photogrammetric systems. The time needed for
the additional manual extraction conforms to
normal production standards of manual DTM
extraction, assuming conventional
photogrammetric systems. This is considered a
loss in the speed and efficiency gained by the
automated DTM extraction capability of the
softcopy system.
Durations were estimated for operator-system
interaction required for standard
stereophotogrammetric procedures. An overall
estimate was recorded for the entire end-to-end
process in the Intergraph system. A detailed step-
by-step breakdown periods were recorded for
Helava. On both cases, interaction durations were
superior to what is expected in a conventional
photogrammetric machine.
132
3.2 Expertise
There is a shift in the kind of expertise required to
operate a softcopy photogrammetric workstation.
This expertise is a departure from what is
normally required for conventional
photogrammetric systems. Characteristics of this
shift can be summarized as follows:
- For operators, less knowledge required in
photogrammetric engineering, as a result of the
"black box" concept, while more required in
computers, Unix, windows, file systems, disk
storage, stereo display, etc.
- For operators, basic system training is sufficient.
- For team leaders, high level training is required,
to ensure smooth flow of operation when operators
encounter a difficult, out-of-usual, situation with
system software/hardware.
4. CONCLUDING REMARKS
-It has become obvious that softcopy
photogrammetry technology does meet
performance standards, even for large scale
mapping, such as WisDOT photogrammetric
operations.
-Substantial gain in speed can be achieved with
softcopy photogrammetric systems, assuming other
bottle necks, such as data volume, are handled
efficiently.
-High end systems do provide at least comparable
accuracy, when automated extraction methods
work. However, substantial enhancements are
needed to add some intelligence in the extraction
process. Matching techniques tend to fail with
simplest unexpected conditions.
-Conversion of conventional production facilities
into softcopy operations requires significant re-
training of operators. Cost issues, data volume,
technical SW/HW support need also to be
carefully considered.
ACKNOWLEDGMENT
This paper deals with aspects of a research project
funded by the Wisconsin Department of
Transportation, under project number 0092-35-57.
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