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As indicated, each time the basic map was revised, the province
began from scratch with new aerial photography,
aerotriangulation, etc. Consequently, little experience in
updating was acquired over the years.
3. SPATIAL INFOSTRUCTURE NEEDS AND
CONSTRAINTS
The government of New Brunswick recognized the importance
of information about land, water and related resources to
manage these valuable resources. In order to establish a
coherence to the government's efforts as they relate to land
information management, in 1989 a Land Information Policy
was established.
This policy ensures that the collective efforts best support the
provinces’ need for geographically related information to set
policies and regulations for land and water use, and for the
resource management. The Policy establishes the Geographic
Information Corporations digital 1:10 000 topographic data base
as the official base on which all other provincial spatially
referenced data will be founded. This collective data base will
have to be updated if it is to maintain its usefulness. How will
it be revised? There are many options. However, funds for
maintaining collective projects are shrinking. In 1992, the
Geographic Information Corporation adopted a Pricing Policy
for its products and services. In the category of existing basic
products and services that involve only maintenance, updating,
and marketing expenses, the pricing method is based on the
recovery of additional costs. In other words, costs for revision
must not exceed revenues from the digital topographic data
base. We are therefore obliged to find more cost effective
methods for revising the infostructure.
The cooperative model (Hamilton 1976) has always been
appealing. Given that there are only a few province-wide GIS
users/producers, it will take some time yet for this model to
reach full maturity. Furthermore, as demonstrated in
Figure 2-1, the digital data of the digital topographic data base
is already over 10 years old in some areas. Some catch-up
techniques will perhaps have to be devised to update the digital
topographic data base. In that light a project was undertaken to
assess the soft colour orthophoto (SCO) product for updating
the digital topographic data base.
4. CONCEPT
The production of most soft orthoimagery and the subsequent
revision of digital topographic data is essentially the same as the
traditional mapping approach. In summary it consists of the
establishment of geodetic control, aerial photography, photo
control, aerotriangulation, block adjustment, collection of digital
terrain data, orthophoto production and interactive revision.
This approach does not lend itself to significant savings.
However, the concept described below bypasses many
traditional phases.
4.1 Geodetic Control
In New Brunswick over 15 000 geodetic control points have
been established between the late 60's and the mid 70's.
Consequently, there is no need for additional control.
4.2 Aerial Photographs
In 1992, the Department of Natural Resources and Energy
undertook a study to decide on the methodology to be used for
311
updating the forest inventory. In the first digital forest
inventory, deciduous species were not included. Because of the
resurgence of interest in these species, there is a need for them
to be inventoried in the next forest inventory. In order to study
the new method of inventorying, a sector of the province that
contained all arboricultural species was photographed. The
pilot project’s aerial photographs included colour photography
at the scale of 1:30 000.
The results of the study were conclusive and the whole province
will be photographed with colour photography at the scale of
1:25 000.
This aerial photography for the project will be taken in the fall,
before leaves fell. If the infostructure is to be revised from
aerial photography the ideal time for taking photographs would
be before the leaves appear or after they have fallen. However,
because colour photography will be available for the whole
province, the use of this photography, if satisfactory, would
entail no additional aerial photography cost.
4.3 Photo Control, Aerotriangulation and Adjustment
The purpose of photo control, aerotriangulation and adjustment
is to establish control to carry out the relative and absolute
orientations of each photographic model. As discussed earlier,
the digital topographic data base will be completed in 1994.
The question raised was as follows: Can the digital topographic
data be used as control to generate the soft colour orthophoto?
If this was successful, costs related to photo control,
aerotriangulation and adjustment would be eliminated.
4.4 Digital Elevation Model (DEM)
During the creation of the digital topographic database, spot
elevations were collected in an irregular grid, 1 mm to 3 mm
at photo scale, (1:35 000 photo) depending on the roughness of
the terrain. Block adjustments were carried out as per the
1:10 000 map accuracy specifications and the spot heights were
read to a 0.1 m precision.
Usually the creation of the DEM is an expensive component in
the orthophoto process. In New Brunswick the DEM collection
is near completion. The question now is: Will the investment
in DEM collection over the last ten years allow the province to
update the digital topographic base at a reduced cost?
5. EVALUATION OF THE CONCEPT
5.1 Partnership
The contract to evaluate the concept was awarded to Universal
Systems Limited (USL) of Fredericton. USL worked in close
collaboration with Northeast Exploration Services Ltd. and
Geomacadie Services Ltd. Northeast Exploration was given the
orthophoto production responsibilities and Geomacadie the map
revision responsibility.
5.2 Selection of Imagery and its Quality
Aerial photography flown to produce vector maps can vary in
quality, within the range of specifications, without having a
great impact on the data. However, aerial photography for soft
orthophoto is much less forgiving. The quality of the aerial
photography used in the project was not the best to produce an
orthophoto. There was a lot of haze and the shadows were at
their maximum. The shadows are large because the photograph
was taken a few minutes from the limit of the minimum solar
