67
.cal Research, Vol.
Symposium on Remote Sensing for Resources Development and Environmental Management / Enschede / August 1986
cloud
ices. Submission to
lospheric effects
the thermal
on satellites. The
iadiometer (AVHRR),
No. 1, p. 161-
Base map production from geocoded imagery
Dennis Ross Rose & Ian Laverty
Macdonald Dettwiler and Associates Limited, Richmond, B.C., Canada
Mark Sondheim
British Columbia Ministry of Environment, Surveys and Resource Mapping Branch, Victoria, B.C., Canada
ABSTRACT: Current techniques of producing topographic base maps rely chiefly
on aerial photography as the data source. Topography and planimetry are
derived using standard photogrammetric methods and manually operated equipment.
Although this method meets current accuracy requirements when used properly, it
has several inherent problems. For instance, the collection of source data is
costly as it involves special aircraft collection missions. Extraction of
relief and feature detail using manual methods is prone to operator error.
Solutions to these problems must provide more cost-effective means of obtaining
data and a more automated approach to information extraction from this data.
During the past decade much progress has been made in the correction and
processing of digital satellite imagery. Techniques such as geocoding have
been developed and refined to the stage where map accurate imagery can be
produced in a high-throughput environment. It is possible for mapping agencies
to use this imagery as an input to many standard mapping operations. Using
technology which is available today, it is possible to accurately derive
planimetric, thematic, and topographic maps using this digital imagery as the
primary source of information.
This paper will discuss the recent advances in technology which have provided
the means to produce such accurate imagery as well as describe how this imagery
can be used to produce quality map products in a production environment.
Topics such as feature extraction, thematic classification, elevation
derivation, and resultant map accuracies will be discussed. A sample 1:50,000
scale base map, derived entirely from LANDSAT TM imagery, will be presented and
evaluated to demonstrate the concepts discussed.
BACKGROUND
The year 1986 will prove to be a very
significant one to both the remote sensing
and cartographic communities. The recent
launch of the SPOT satellite and the ability
to generate LANDSAT-TM and SPOT precision
geocoded products will, for the first time,
allow cartographers to use
digitally-processed satellite imagery as a
prime data source for map production.
Satellite imagery is economical and provides
high information content. Production
oriented mapping systems are now being
developed which extract feature and relief
content entirely from imagery. General
acceptance of these systems will only come
about once it can be shown that the
satellite derived map products compare
favorably to those generated by typical
photogrammetric techniques.
Current mapping procedures are based on
photogrammetric methods and meet required
accuracy standards. However, several
problems exist with such methods. The
procedure is slow and data acquisition is
expensive. Resultant quality may vary from
interpreter to interpreter.
Developed nations often have well developed
mapping programs. Such countries continue
mapping to update existing maps or to
improve the accuracy of existing maps.
Developing nations frequently have not been
mapped completely, and any existing maps may
not be of acceptable quality. Such
countries cannot afford the time (often
decades) or cost required to produce a
quality map data base.
Digital satellite imagery should provide
help for both of these cases. Satellite
imagery provides very wide region coverage.
A single LANDSAT-TM image covers an area of
34,000 sq. kilometres, compared to a 130
sq. kilometre aerial photograph (1:50,000
photo scale). Similarly, the amount of
ground control required to correct a
satellite image is one tenth of that
required to correct a corresponding area of
aerial photographs. These differences imply
a highly reduced cost of data acquisition
when comparing satellite imagery and control
to aerial photography and control.
The digital and multispectral nature of
satellite imagery also provides advantages
over aerial photographs. Using digital
techniques it is possible to ~ extract'
terrain, planimetry, and landcover
information in an automated fashion from the
imagery. Since the infomation is digital,
it can be used easily with other digital
data (e.g. digital maps). Finally,
automated map production will lead to more
consistant quality map production, as human
intervention is reduced.
