70
imagery, with a pixel size of 30 metres and
a base-to-height ratio of 0.1, is limited to
an elevation accuracy of at best 60 metres
RMS. SPOT stereo imagery, with a pixel size
of 10 metres and a base-to-height ratio of
0.5-1.0, should produce an elevation
accuracy of about 10 metres RMS (Cooper,
Friedmann, and Wood, 1985). This is
suitable for 1:50,000 scale mapping (and
larger scales for many applications).
The SPOT PLA imagery should meet typical
1:50,000 scale map content standards, except
in the detailed interpretation of some
cultural features, where aerial photographs
are also limited. Natural planimetric
features can be interpreted accurately
enough for 1:50,000 scale maps from
LANDSAT-TM or SPOT.
COSTS
The costs involved in the production of
topographic base maps vary greatly,
depending on the type of terrain being
mapped, and the type of mapping being done.
However, typical figures can be used for
compa rison.
The costs for digital mapping methods are
usually broken down as follows: ground
control, aerial photography, photogrammetric
feature and terrain extraction, editing,
verification, and plotting.
In Canada, the cost of obtaining ground
control ranges from $400 to $8,000 per
control point depending on terrain and
location. Using a minimum of five control
points per map, control could cost $2,000 to
$40,000 per map. Using the satellite
mapping technique, the required control
drops from five per map to seven points per
sixteen maps, or about one control point for
every two maps ($200 to $4,000 per map).
The cost of obtaining ground control is
one-tenth of that required for
photogrammetric purposes.
The cost of obtaining image data for
elevation and planimetric extraction is
considerably less than obtaining aerial
photographs. LANDSAT-TM imagery costs about
$0.09 per square kilometre. SPOT imagery
should cost about $0.60 (projected U.S.
price) per square kilometre. This compares
to a cost of about $1.50 per square
kilometre for new high-altitude aerial
photography.
The current cost of terrain and planimetric
extraction for 1:50,000 scale maps, produced
in Canada, is approximately $25,000. This
is divided evenly between planimetry and
topography. Through the use of the
automated elevation and planimeteric
extraction techniques discussed in this
paper, it should be possible to perform the
same function on the computer for under
$7,000.
Total costs of the satellite image-derived
map should be about $10,000 per map (This
includes all steps from control and image
acquisition through to map plotting). This
compares to current costs averaging $50,000
per map using photogrammetric methods.
SUMMARY
Satellite imagery can be corrected to a
planimetric accuracy suitable for 1:50,000
scale mapping. When corrected with accurate
control points and removal of terrain relief
error, both LANDSAT TM and SPOT imagery can
meet NATO class "A" standards for 1:50,000
mapping planimetry. LANDSAT stereo imagery
does not provide sufficient resolution or
base-to-height ratio to meet elevation
accuracy standards for 1:50,000 mapping.
However, SPOT stereo imagery with increased
pixel resolution and a larger base-to-height
ratio should produce elevation accuracy of
about 10 metres RMS. This translates to a
20 metre contour interval for 1:50,000 scale
mapping.
The sample map shows the feasibility of
producing base maps from satellite imagery.
By integrating all of the components used to
produce the map into a single, tightly
linked system it will be possible to produce
such map products operationally in a very
high throughput environment.
A map with content based solely on satellite
imagery can be produced in less than 24
hours, compared to weeks by photogrammetric
methods. Automatic processing steps would
be performed by the computer unattended
overnight, leaving the machine free for
interactive work during the day. (This
assumes that imagery and control data is
available already and neglects physical
plotting time). It includes input,
correction, and geocoding of the imagery,
and extraction of elevation, planimetric,
and thematic data.
The cost of such techniques would be about
$10,000 per mapsheet including field
acquisition of new ground control suitable
for correcting satellite imagery (these are
current best estimates). Comparable costs
for photogrammetric mapping average at
$50,000 per mapsheet. These figures are
based on steady state production as part of
a long-term program, and include capital
equipment depreciation and labour as well as
data costs.
The potential for mapping from satellite
imagery appears to be great. Using existing
technology, a sample map has been created
and demonstrated in this paper which shows
the potential feasibility of such mapping
systems. In the near future, fully
integrated mapping systems will be developed
which will produce cartographically accurate
maps from raw satellite imagery. Such
systems will be both economical and fast
when compared to conventional techniques and
will provide new products to the mapping
community due to the digital nature of the
source data (see Figure 3).
FIGURE 3 - 3-D View of Adam River
(LANDSAT Imagery and Derived DTM)
Cooper,
S .A. ,
Digital
Images
36th
Congress
Friedman
Magnusse
S., "Mul
Spacebor
Control
Engineer
49, No.
1983 .
Gue rtin,
Potentia
Products
Canadian
Winnipeg
Welch, R
"Compara
Accuracy
Landsat-
Image Da
and Rem
pp. 124
Welch, R
SPOT
Engineer
51, No .
Yee, B.
Sondheim
for Smoo
accepted
INTERFAC
1986 .