- Combined environment -ArcCAD & AutoCAD:
ArcCAD is the GIS engine for AutoCAD, that is why we
can work in a full 3D CAD environment and when is
required to use GIS commands the database is
transferred to GIS structure and spatial analysis
commands can be selected.
The transfer to a GIS database structure consist of
three phases; define a "theme" and a dataset, copying
the relevant layer to that "theme", and finally cleaning
the dataset/"theme", automatically the required GIS
database files are created.
In addition is always possible to shift and use the
powerful CAD commands within the GIS.
3.2 System modules
Figure 2 illustrates the flow chart of activities and the
developed modules of the proposed system.
Manually input layer |
Trees & vegetation
House eaves & Bridges
Relief displacement
Calculation
of
uncertainty
area map.
Shadow areas
Comparison to other sources
GPS planning |
Field completion planning Total station planning
ror"
Building classification.
Identifying electricity utilties |
|
| Special requirements
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m
Field completion user-interface.
Record telephone-network
| a 3
Insertion of drainge system
T data editing
| -] | Error computatior]
An estimation of completion work]
Quality estimation |
Metadata production
Figure 2 : System Flow-Chart
3.2.1 Uncertainty map calculation module
This module is the core of the system, includes spatial
diagnostics of the initial database, created by
photogrammetry, and presentation of the
photogrammetrically obscured areas ( relief
displacement, sun shadows, covered areas, etc. ).
Furthermore, does a geographic comparison of the
database produced by photogrammetry and other
available geospatial sources to detect missing objects.
This operation uses GIS overlay functions to indicate
disagreements between the positionally accurate
database (i.e., collected by photogrammetry) and the
thematically accurate database (e.g., electricity
network map).
There are six components that together produce the
146
map of uncertainty:
- Manually inserted layer - This layer is produced by
the photogrammetric workstation operator. The
operator marked the areas he was unsure of details or
were invisible due to irregular conditions such a cloud
cover, atmospheric haze, smoke clouds, hot spots etc.
- Trees and vegetation - Those layers are marked
automatically as uncertain because features under
these objects are invisible. However the user can give
an area threshold in square meters and the software
marks only those polygons that are bigger than the
threshold.
- House eaves and bridges - When there is a request
to map foot prints of houses, the distance between foot
prints and roof lines should be measured in the field.
Moreover details near or under bridges may be of
interest. In this module a layer with the appropriate
information is produced.
- Relief displacement - The program computes the
relief displacement of each building. It takes each point
in the polygon and shifts it according to its height. The
shifting is done from each vertex in the direction
opposite to the projection center. Connect all the
shifted points to each other and to their original
position.
A layer of displacement (named "disl") is produced.
The program advances to the ArcCAD environment,
first defines "theme" and "coverage" from the
appropriate layers (e.g., data-set "house" from layer
"2200" and data-set "shade" from layer "disl"), then it
cleans dataset/"theme" and the database can be
managed from the GIS system. Next the program
uses ArcCAD analysis function "erasecov" to erase
features from a theme that overlap with features in
another theme (see figure 3)
The result is the final theme called "disl", which is
"shade" minus "houses" and is displayed in red.
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Er asecov
Huse
Fal i ef
Figure 3 : The Erasecov operation
d sl
d spl acnent
- Shaded areas - The programme examines the entire
project area and presents the parts that are obscured
and blanked out by the presence of shadows. Terrain
features like buildings, cliffs and precipitous relief can
cast shadows over pertinent details and it is for the
field surveyor to measure these details. The user
inputs the sun's angular altitude, then with a similar
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996
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