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photography. The DEM generated on a 50m grid 
which resulted in 332 800 elevation posts with an 
estimated RMS of 1.5m. Contours were generated 
as well, and 3D contour inspection was performed 
by draping the contours on the stereo-model for 
stereo-interactive contour editing. 
The orthoimage was produced pixel by pixel using 
the collinearity equations and the gray values are 
assigned using the nearest neighbour interpolation 
resampling technique. The output ground pixel size 
was set to be at 2m, which was determined as the 
average value between the scanning and the human 
eye resolution of 10lp/mm  (Armenakis et al., 
1995). 
To cover the entire map data set in a seamless 
way, the individual orthophotos were mosaicked 
and radiometrically corrected. Due to the large 
size of the mosaicked raster file (208Mb) the 
sheet was divided into four orthoquads with each 
quad being a more manageable 52Mb. The 
orthoquads were exported along with geolocation 
data to the CARIS GIS system where they were 
used as raster backdrops for the revision process. 
4.2 Data revision 
The revision of the 1:50 000 NTDB (National 
Topographic DataBase) vector data based on the 
digital orthophotomosaics was done using the 
CARIS GIS. The metric accuracy of the registered 
orthophotomosaics was evaluated by measuring 
the coordinates of check points from the 
orthophotomosaic and comparing them with given 
values. For the four quads used for the revision of 
the Jasper data, the standard deviation of the 
coordinate differences were from 41.17 to 
+1.67m in x and from +1.50 to +2.69m in y, 
sufficient to meet the NATO A rating planimetric 
accuracy requirement for the 1:50 000 maps. 
The criteria for collecting new data or revising 
existing features were based on the following 
factors: 
- the amount and type of change detected 
- the accuracy of the existing feature 
- the topology 
- the feature morphology, and 
- the significance of the feature. 
The orthophotomosaic quads were displayed one at 
a time and the CARIS file manager utility was used 
to integrate the raster and vector data to 
facilitate the use of superimposition for the 
collection of the new data. A tile approach was 
used for the revision process, where the operator 
97 
steps through the data set in small virtual map 
tiles, revising all the features before moving to 
the next tile. The task of visual change detection 
was aided by relying on photo-prints from the 
field verification for classification of roads, noted 
additions, deletions and changes to features. The 
zoom in/out capabilities were applied for data 
collection. Image interpretation was 
improved/assisted by employing interactive 
contrast enhancement using either histogram 
equalization or user specified histogram. During 
revision the selective display of features was 
applied for best results. In conjunction with the 
display on screen, the operator used a stereoscope 
and the aerial photographs with field information 
to view the area's relief, identify features such as 
watercourse, permanent snow and ice (glaciers) 
and collect them with greater ease. Figure 2 
shows the “old” and the revised “new” vector 
data of the Athabasca River features. 
The data set for Jasper map sheet was vectorized 
cartographic data and required a slightly different 
approach for revision than a positional data set. 
When revising a positional data set, the exact 
positional data would be collected. In the case of 
the revision of a cartographic data set, features 
that were not positionally correct due to 
cartographic displacement are not re-positioned. 
Repositioning these features would only result in 
additional work at the cartographic editing stage, 
although it may be considered to improve the 
accuracy of the NTDB vectorized “old” data. To 
determine if a feature was positionally incorrect 
or just cartographically displaced, the 
cartographic utility WYSIWYG was found very 
useful. The WYSIWYG capability allowed the 
operator to turn feature symbology on and view 
the feature with its cartographic representation. 
For example, a railroad that was positionally 
displaced, but shown to be cartographically 
correct with it's symbology displayed, was not 
edited. 
Attribute changes in the data were applied based 
on information collected during the field work. The 
height information of the planimetric features can 
be derived from the DEM used to produce the 
orthoimages either in real-time or in post- 
processing mode. For the revision of this map, new 
contours were automatically generated from the 
DEM for evaluation purposes only, and the existing 
metric contours were maintained. 
The revised data was time-stamped. This enabled 
the revision operator to identify all the features 
that have been revised and separate them from the 
original data for quality control. 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996