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A RULE-BASED SYSTEM FOR THE EXTRACTION OF CARTOGRAPHIC
FEATURES FROM LANDSAT TM IMAGERY
M. Stadelmann
G.D. Lodwick
Department of Surveying Engineering
The University of Calgary
2500 University Drive N.W.
Calgary, Alberta
Canada T2N 1N4
Prepared for ISPRS COMMISSION VII Mid-term Symposium, Victoria, B.C., Canada, September 1990.
ABSTRACT
This paper describes work that has led to the development of a basic rule based system for the automated
recognition of cartographic features in digital satellite imagery. The system uses frames to represent
knowledge and is written in Arity PROLOG. Input to the rule based system consists of a segmented image
modelled as a polygonal database. Image segmentation is carried out on the multispectral data using a
migrating-means clustering algorithm. Simple landuse features, such as fields and water bodies, are extracted
using spatial information, such as object areas, and simple shape measures, such as compactness ratios,
combined with spectral knowledge. For more complex features, contextual information, such as adjacency,
and more complex shape measures, such as elongation, are extracted from the image database. Results have
been compared with conventional image interpretation and show acceptable accuracy, provided image
segmentation errors are moderate. These conditions are met in images depicting rural areas as they contain
spectrally homogeneous features. In more variable environments, such as urban areas, more advanced
measures of coping with segmentation problems and the use of ancillary information are expected to generally
enhance the success of automated image interpretation.
KEY WORDS: Automated, digital, interpretation, mapping, cartography, Landsat, remote-sensing, GIS.
1 INTRODUCTION
Earth observation satellites, such as the Landsat
series or more recently SPOT, have the potential to
facilitate map production and revision, as well as
aid in the management of natural resources. They
are particularly useful because their high
resolutions and repetitive coverage permit the
detection and monitoring of temporal changes on a
regional and local scale. However, the increasing
resolution poses the problem of increasingly large
data volumes, which must be analyzed and
managed (Maslanik and Smith, 1984).
Electro-optical sensors capture data in digital
format suitable for computer processing. However,
automated feature extraction has mainly been
restricted to statistical classification methods, which
distinguish between surface cover classes on the
basis of spectral signatures. The interpretation of
the images, i.e. the assignment of meaningful
names to cover classes, has remained a manual
task, because image interpretation, in addition to
spectral knowledge, requires a considerable amount
of contextual information. Extraction of this type
of information requires human expertise and
decision making which cannot readily be
accomplished using traditional algorithmic
methods.
In the conventional map production process,
image interpreters typically analyze a satellite
image and transfer any objects of interest manually
onto a map. A GIS data base is then usually
produced by digitizing these map products, which
have already undergone abstraction and
generalization compared to the original remote
sensing data (McKeown, 1987). GIS products
therefore usually result from one or more thematic
map overlays.
Image interpretation is a slow process which
requires highly skilled personnel. Digitization and
integration into the GIS data base is tedious and
error prone. For example, if an image polygon is to
be placed in the GIS, data base corruption will occur
if there is no perfect juxtaposition of the image
polygon and neighbouring map polygons
(Goodenough et al., 1987). In addition, the accuracy
of a finished map product decreases considerably if
two or more digitized map overlays are utilized in
its production (Newcomer and Szajgin, 1984). The
time involved in image interpretation and quality
control of map products in GIS has created a
bottleneck in spatial data handling that has to be
eliminated if resources managers and planners
wish to make efficient use of the technology
available to them.