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Department etc.--
- transferring the collected data to digital form. This is
done with digitizing tables connected to a computer
with a CAD software. The operator needs to have the
photogrammetric database as a Source for
georeferencing, i.e., the additional information is
positioned according to prominent features which
appears both in the photogrammetric database and in
the map.
C. Database analysis - This phase is actually the
weakest part in the chain of normal mapping
procedures. In the proposed work flow, plays an
important role.
The operator during the photogrammetric data
collection phase inserts in a specific layer the areas
that were unclear, uncertain and where he thinks it
should be a closer investigation, from the field
surveyor.
The developed software analyses, shows and marks
all the uncertain areas and produce a comprehensive
map of field completion work.
This map includes; the areas designated for field
completion during the planing stage, zones that were
sun shaded, regions covered by trees and vegetation,
with obscured areas due to relief displacement, and
objects or places where was a dispute between the
different sources of information and, of course, those
areas marked by the photogrammetric operator as
doubtful.
Following the software menu the user can plan the
field work activities and choose the surveying methods
to be used.
There are two software modules one is aimed at
surveying using total station and portrays the areas
that are invisible from particular ground points, while
the second module is intended for GPS surveying and
presents the areas that cannot be surveyed by GPS.
D. Field completion: Field completion, being time
consuming and costly operation it should be performed
in the most effective way. We propose, the field data
collection to be done, using a portable computer and
especially designed software. The CAD software can
present the initial digital map in any required scale,
can also edit and modify it in the surveying site. The
developed functions are used for quick insertion of
new elements using common surveying techniques
arcsection/right angle /distance & direction and also
data collected from surveying instruments. The
surveyor does not need to remember all the lists of
symbols with their defined layers but rather to navigate
quickly through the menus.
E. Quality control - One of the objectives of field
completion is to verify and check that the map
145
conforms to a certain accuracy specification. Our
software prompt the user to identify check points and
to input their measured position. At the end of the work
and after the collection of a sufficient number of points,
the software computes quality parameters based on
the coordinate differences, and adds this important
information into a metadata file (a file with relevant
information describing the geodatabase).
We can clearly see that using this approach, the
integration between photogrammetry and field
completion becomes stronger and more natural, the
GIS/CAD software indicates the areas of field
completion and enables the insertion of the collected
information directly into the database.
3. SYSTEM IMPLEMENTATION
3.1 Programming considerations
The system is a LISP program written in ArcCAD
software environment. Input into the system is the
initial database (the outcome of stages À and B in
Figure 1). The initial database consists of graphical
elements, i.e., points, lines, polygons and symbols
arranged in the database in "spaghetti mode".
Three important features are used extensively in the
developed modules:
- Layer structure: :
The graphical elements in the "Spaghetti" file are
divided into layers, each layer contains the graphical
elements that belong to a group of objects, e.g., layer
"2200" contains all the polygons that represent
buildings/houses, layers 2801 contains individual
trees, etc.
Consequently the basic tool that allows to select a
group of objects, is the layer separation. For example
when we want to display only the trees in the database
we select layer 2801 and we "freeze" the other layers.
The layer structure is also used when new information
is produced, e.g., when the sun-shaded areas are
evaluated the corresponding polygons are placed in a
new layer called "shad".
- Blocks and attributes:
An important element in AutoCAD is the block. A
block, like a symbol, is an ensemble of simple
graphical elements (points & lines). However, unlike
symbol elements, there are attributes attached to the
block. An attribute is a textual descriptor or additional
information of the object. The block is a convenient
tool for insertion of data, because during the insertion
of a block the user is requested to fill the attribute
information, i.e., most questions that will be the block's
attributes. Block attributes can be visible or invisible
and they can be transferred from the graphic data file
to a tabular database.
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996
