Symposium on Remote Sensing for Resources Development and Environmental Management / Enschede / August 1986
Automatic digitizing of photo interpretation overlays
with a digital photodiode camera: The ADIOS system
C.A.de Bruijn & A.J.van Dalfsen
ITC Department of Urban Survey and Human Settlement Analysis, Enschede, Netherlands
ABSTRACT: The rapid introduction of geoinformation system in various fields of planning and municipal
administration creates an urgent need for efficient methods to input information obtained by visual
photointerpretation.
The paper describes the ADIOS system for "automatic digitizing" of photointerpretation overlays, currently
under development at the ITC Department of Urban Survey and Human Settlement Analysis.
A digital camera with 2048 x 2048 pixel resolution is used to scan landuse interpretation overlays. After some
processing to improve the quality of the scanned lines, the landuse codes of each polygon are added, from a
centroid file or during an interactive session at a color graphics terminal. Resulting data can then be sent
to a geoinformation system like USEMAP for geocorrection and further processing.
1 INTRODUCTION
Aerial Photography can supply planners of fast
growing cities with thematic information on landuse,
residential patterns, site suitability, traffic
behaviour, etc.. Often such information is difficult
to get by other means. Visual interpretation will,
for the time being, remain the predominant technique
for data extraction from airphotos, especially in
urban areas with complex spatial structures.
However, data obtained in this way have to fit in
the geo-information systems that will increasingly
be adopted by municipal authorities for their
spatial datahandling, both thematic and topographic.
Since 1973 various methods to input photo
intepretation data in geodatabases have been
developed at ITC as part of the USEMAP software.
Starting with manual gridencoding they now rely
mostly on manual digitizing.
Valuable results have been obtained in various
projects. The use is rapidly increasing and has
created new possibilities in linking thematic survey
data closer to their eventual applications.
Still, manual digitizing is far from optimal and as
pointed out by TOMLINSON (1980) digitizing one of
the main problems in the field of geodataprocessing.
Better, faster and more accurate input methods are
urgently required if airphoto interpretation is
going to remain an efficient datasource.
2 VARIOUS METHODS OF DATA INPUT
Entries in a geodatabase consist usually of two
elements: a spatial description (location of point
or area) and attribute information (thematic
information about the point or the area, e.g.
landuse). The spatial description of an area can be
in the form of lines (vectors) defining the limits
of the area, or in the form of gridcells (pixels)
that are marked as belonging to the area. Choice
between lines and gridcells has been the source of
much debate in the past, but the development of
modern hardware has made it rather irrelevant, since
it has become fairly easy to convert from one
datatype to another. However, at present "large
scale" topographic databases are usually vector
databases, while "medium and small scale" thematic
databases tend to be gridcell databases.
Interpretation data can be entered into a computer
database by coding gridcells, (now rather obsolete),
manual digitizing (the most common method) or
scanning.
Manual digitizing during interpretation may distract
the interpreters’ attention and is certainly not
feasible for all types of interpretation, while
digitizing after interpretation means an additional
step in the survey process, it may delay the final
results and introduce additional errors.
Either way, digitizing remains a time consuming
obstacle, when data are to be used in a digital
environment and at some places a tendency has been
observed to use lower quality satellite Remote
Sensing data instead of data from airphoto
interpretation "because the data are already in
digital format". The introduction of more efficient
data input methods is therefore of paramount
importance to ensure the continuing usefulness of
airphoto interpretation.
In 1981, based on earlier work by MEISNER (1981) the
first author wrote a research proposal to develop at
ITC a "digitizing machine" based on a high
resolution CCD camera. The proposal called ADIOS
(Automatic Digitizing of Interpretation Overlays
System) was accepted in 1982 but acquisition of the
required hardware was complex and time consuming due
to the absence of representatives for this type of
digital cameras in Europe. In October 1985 an
Eikonix 78/99 digital camera arrived at ITC and
development of application software and testing of
various methods could eventually start in 1986.
3 EMPHASIS ON PHOTO INTERPRETATION OVERLAYS
The starting point of the ADIOS concept is that the
normal visual stereoscopic photo interpretation
should not be affected by subsequent digitizing
procedures. The automatic digitizing should be based
on the "interpretation overlay", the transparancy
containing lines and codes which forms the end
product of most regular interpretation jobs, (fig.l)
