the impact of GPS techniques, and the ready 
availability of ground control points in an 
effectively standard reference system (WGS 
84), greatly facilitates the registration, in 
practice, of remote sensing and GIS or map 
data. 
A review of recent literature in the fields of 
GIS and remote sensing reveals that there is 
considerable interest in the integration of 
remote sensing and GIS. Sadler et al (1991), 
for instance, use census data in an attempt to 
improve the classification of urban areas. 
Census areas held in vector from are processed 
to generate a continuous surface raster dataset 
of population density value. This is then used 
as a pseudo 'image plane' in a classification 
process. 
Janssen et al (1990) describe the use of a 
topographic map to classify an image on a 
'per-object' basis. However, as the systems 
used (leading GIS and image processing 
packages) have no capabilities for integrated 
processing of this type, they rasterise map 
objects and then use these as a mask within a 
self-developed program for assessing the 
dominant class within the objects, from an 
image classified using a standard per-pixel 
classification process. 
The conclusion inevitably reached, therefore, is 
that a level of integration substantially beyond 
co-existence of image processing and GIS is 
required. The statement: 
"The integration of image data into GIS is 
one of the great ideas whose time has 
come" (Faust et al, 1991) 
is now extremely relevant, whilst the 
statement: 
"Remotely sensed images have been shown 
to be a cost effective means for update of 
GIS data" (Faust et al, 1991) 
is clearly demonstrable. The chief operation 
that can be said to date to effectively integrate 
remote sensing and GIS is heads-up digitising. 
However, this has been due to the limited 
386 
capabilities of software packages: further 
benefits of integration remain to be realised. 
3. THE FUTURE FOR INTEGRATION OF 
REMOTE SENSING WITH GIS 
The first important distinction to make is 
between remotely sensed data and raster data 
(which may, of course be, or be derived from, 
remotely sensed imagery). Most references to 
'integration' refer to the integration of raster 
data with vector processing functionality. 
Although integrated data processing can utilise 
data in both raster and vector forms, it is still 
necessary for the output data to be held in one 
form or another. For instance, a function to 
classify an image on a per-object basis will 
output data as an attribute of a vector object, 
and a function assessing land suitability for 
development might output data as a single 
raster ’suitability’ value. 
Processing functionality that genuinely 
integrates GIS data with remotely sensed data 
can be divided into two groups: 
e Functions that enhance image processing 
operations. 
* Functions that enhance vector operations. 
These generally make no distinction 
between the use of remotely sensed imagery 
and of any other raster dataset. 
4. FUNCTIONS THAT ENHANCE IMAGE 
PROCESSING OPERATIONS. 
There are three main areas where GIS data can 
be used to enhance standard image processing 
functions: 
4.1 Geometric correction. 
Conventionally, ground control point (GCP) 
co-ordinates are input to an image processing 
system as an image is being rectified. If the 
system can display and manipulate GIS data, 
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