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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B3. Istanbul 2004
reference profile can be specified and the tracking of the line can
be continued. Where the linear feature has been extracted
completely, it is closed, and the next line segment can be
captured. Figure 6 shows a typical situation during the
acquisition of a road network.
Interactive
initialization
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Determination of
the reference profile
|
No Prediction of
the next point
i
Measurement of
the next point
|
Fusion of prediction
and measurement
Stop
tracking?
Task dependent
interaction
Figure 5. Flow chart of the line following algorithm
Figure 6. Line extraction of a road intersection. The different
road segments are topologically connected by a node.
The width of the line is automatically determined based on the
assumption that the linear feature is bordered by more or less
parallel grey value edges.
Before the line is stored in the database, it is smoothed and the
number of vertexes is reduced using the algorithm presented in
Ramer (1972).
S. RESULTS
The semi-automatic feature extraction software was designed to
operate as a vector data acquisition and update component in a
distributed GIS environment. We decided to use the OpenGIS
standard GML for vector data import and export, because it
enables the integration into an open GIS infrastructure. GML
can be applied for interoperability between different
organisations and companies, which has already been
cessfully tested (Feldman & Curtis 2003).
The feature extraction is preferably done in digital orthophotos
for the capture of 2D GIS vector data. In addition, the software
is available for the capture of 3D features using oriented aerial
imagery. Here the automation part consists currently of the on-
line z measurement functionality which automatically derives
the height of each vertex point of a line feature or the contour of
an area feature. The algorithms have been extensively tested
with IKONOS 2 and IRS satellite imagery as well as with
orthophotos. Figure 7 shows the result of extracted VMapl
features from an orthophoto with 50 cm pixel size.
Figure 7. Extracted line and area features from an orthophoto
6. CONCLUSIONS
inJECT is one of the very few software developments in
automated feature extraction that have been implemented as a
commercial system. The software has been substantially
extended with new automation modules and a strong GIS
interface. The software basis of inJECT has been proven to be
an excellent platform to add and test external software modules
that increase the automation level significantly. By adapting the
OGC-defined GML standards the field for future applications is
wide spread. The developed GIS interface to Dynamo and
GeoMedia opens the window to many applications in those
fields. Our solution has major advantages compared to many
GIS data acquisition packages that do not allow such user-
friendly data capture and updating, especially not in 3D. It has