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procedure as in the relief displacement module, the
layer "shadl" with sun-shadows is produced.
. Comparison to other sources- In this module a
comparison is made between the database, collected
via photogrammetry, with other sources like
municipality maps, telephone and electricity network
maps etc., to monitor possible missing features.
Basically this module is using two ArcCAD functions
"buffer" and "erasecov" and with those functions it
present the missing objects.
The user inputs the names of layers to be compared
and the search area radius (this parameter is variable
depending on the positional accuracy of the digitized
map).
3.2.2. Field completion planning.
The information about the amount of obscured areas,
missing objects, the type of areas to be completed and
possible special requirements, are at this point known.
The surveyor has to choose the surveying method to
be used in the field work --GPS, total station or simple
measuring tape--.
Interactive analysis of the surveying sites is done to
plan the field work. This module performs line-of-sight
predictions for total station survey and satellite
masked areas evaluation for GPS measurements.
Consequently, there are two modules in the system
one for GPS and one for total station.
GPS planning: The aim of the GPS planning module
is to portray the areas that will be masked from
satellites and therefore cannot be measured by GPS,
or while surveying with a GPS in a kinematic mode
those areas should be avoided, otherwise "lock" it may
be lost and GPS initialization is necessary.
Furthermore the program presents the known control
points that may be used for the project. There are
distinguished in benchmarks and triangulation points.
In this way the surveyor can design the GPS network
before field work.
Total station planning: The objective of this module
is to assist the surveyor in planning his work if total
station is going to be used. The program present the
known control points classified according to their
accuracy levels, e.g., « 10 cm. Next, a choice is made
of a point for instrument position, to maximize
command of the terrain to be completed, and having
visibility to control points.
3.2.3 Special requirements.
This module addresses the special requirement of the
client that is to say the customers' specifications.
Spacial tools for collecting additional types of
147
information such as electricity network elements,
building classifications, telephone utilities, drainage
systems, etc., are provided in this module.
3.2.4 Data insertion & data editing.
This module was developed to serve the surveyors in
the field in the data acquisition procedures. The data
collection user interface provides the surveyor with
most useful geometric functions to insert new objects
directly into a portable computer according to the
required data model. These surveying functions
include arcsection, right-angle prism, polar positioning,
etc., and they enable rapid data collection using a
simple measuring tape. Moreover the CAD
environment comprises many functions and operations
to display, edit and add new information.
3.2.5 Quality estimation.
Quality control, is based on field measurements. The
system checks if the map conforms to the accuracy
requirements. The surveyor makes a number of
measurements to verify the relative accuracy and a
number of measurements to check absolute positions.
Finally the software produces a report which describes
the database, its accuracy parameters and the number
and type of details that were newly collected and
inserted in the data base.
4. FURTHER IMPROVEMENT AND CONCLUSIONS
We have presented a system that can intelligently
envisage all the uncertainty zones that require field
completion surveys in the production of geospatial
databases. The developed software provides
analyzing tools that injects intelligent and global
consideration into every step of the field completion
operation. Initial experiments have shown that this
concept of using GIS for the planning and analyzing of
field completion work is effective and improves the
data collection productivity. It should be noticed that
the system can be useful not only for field completion
tasks but also for mapping projects where an initial
database does exists, e.g., database revision projects.
However there are few system modules that can be
improved, and we are in the process of improving
them.
- Obscured areas algorithm - The models used for
calculating relief displacement, shading and GPS
masked areas, use the absolute Z coordinates minus
the average ground level of each object vertex to
calculate the shift. That model is good for flat areas.
Nonetheless, if the ground height changes rapidly then
we need to subtract the local height from every point
(i.e., for every point we need to have its height
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996
