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EVALUATION OF SPOT DATA FOR TOPOGRAPHIC MAP REVISION AT 
THE NATIONAL LAND SURVEY OF SWEDEN 
Bo Malmstróm 
National Land Survey 
S - 801 82 GÄVLE 
SWEDEN 
Agneta Green Engberg 
Swedish Space Corporation 
P.O. Box 4207, S - 171 04 SOLNA 
SWEDEN 
Presented at ISPRS, Washington D.C., August 2-14, 1992, Commission IV 
ABSTRACT: 
In a project carried out jointly by the National Land 
Survey (NLS) and the Swedish Space Corporation 
(SSC), SPOT data has been tested for map revision 
purposes. The main application focused on is a frequent 
revision of the new topographic map series at the scale 
of 1:50 000. The map features of current interest are 
roads, clearings and built-up areas. Comparison has 
been made with aerial photos. Results show no or minor 
differences in interpretations of roads and clearings 
from aerial photos, SPOT PAN or SPOT XS regarding 
the different accuracy measures: completeness, shape 
and geometric accuracy. For urban areas, it is possible 
to interpret the delimitations of new areas for revision. 
The result also indicate that training is needed to fully 
take advantage of the multispectral images of SPOT. 
Costs and accessibility for SPOT data vs aerial photos 
are evaluated. Current work involves digital revision 
methods with SPOT data at NLS. 
KEY WORDS: Topographic Map Revision, SPOT Data, 
Satellite Remote Sensing Application, Image Interpre- 
tation, Digital Revision Methods. 
1. BACKGROUND 
1.1 The new topographic map of Sweden 
In 1990, the first map sheets of the new topographic 
map series in Sweden at the scale of 1:50 000 was 
published. The maps are produced by the National 
Land Survey of Sweden (NLS, in Swedish: Lantmäteri- 
verket) in Gävle. The new map series is produced 
completely by digital methods. All objects are stored in 
digital databases. The maps also contain an increased 
amount of feature types compared to earlier maps, e.g. 
clearings, bedrock outcrops and cultivated areas. The 
new map is based on aerial photos and field control. 
Introducing clearings in the map requires a rather 
frequent revision interval. The planned revision cycle of 
the new map series is: a frequent revision every 5 years 
involving a few map feature types; an extended revision 
every 10 years concerning a larger set of feature types; 
and finally production of a new map including field 
work after 20 years. 
557 
Revision here implies image interpretation without field 
control. What type of image material, i.e. satellite 
imagery or aerial photos from different altitudes, to be 
used for these future revisions has not yet been decided. 
1.2 The SPOT satellite 
The French SPOT earth resources satellite carries high 
resolution sensors producing data and images of the 
earth. The panchromatic (PAN) mode has a pixelsize of 
10 meters and the multispectral (XS) mode, in the 
visible and near-infrared part of the electromagnetic 
spectrum, has a pixelsize of 20 meters. Sweden coopera- 
tes with France in the SPOT project, and the two main 
receiving stations are situated in Toulouse, France and 
in Kiruna, in the far north of Sweden. 
SPOT is a near-polar orbiting satellite covering the 
earth in 26 days. SPOT carries two sensors which can, 
besides nadir viewing, be programmed to point off-nadir 
to the side of the current satellite track. With nadir 
viewing a certain satellite "scene" is revisited every 26 
days. The further away from the equator, the closer the 
distance is between the satellite tracks, causing overla- 
ping scenes. In central Sweden, for instance, a particu- 
lar area on the ground is covered approximately every 
13 days with nadir viewing. Using the pointing capabili- 
ty, however, the revisit cycle dramatically increases to 
a matter of day or days, all depending on the latitude 
and the pointing angle of the sensor. 
2. AIM OF THE STUDY 
The main objective for this study, carried out in coope- 
ration between the National Land Survey and the 
Swedish Space Corporation, was to find out if SPOT 
images could be a used in the interpretation process for 
the future frequent revision of roads, clearings and 
built-up areas in the new topographic map at the scale 
of 1:50 000. 
The alternative method for this revision type would be 
using aerial photos from high altitude (9 200 meters, 
negative scale 1:60 000) or very high altitude (13 200 
meters, negative scale 1:150 000). 
Costs and accessibility were also to be investigated.