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line, racetrack, highway bridge, buildings and edge of 
forest. All features were digitized in point mode. Roads 
were digitized along the centre line. 
The newly digitized features were then combined with the 
original map and the position of the features in the original 
map were used as the reference to ascertain the accuracy of 
the revision process. Point features were tested by forming 
the coordinate differences. Line features were subdivided 
into sections at well defined breakpoints. Thereafter, X, Y 
coordinates were generated at equal intervals along the 
original and newly digitized path of the features. The 
deviations at corresponding point pairs were then computed. 
A total of 977 points of well defined features were tested in 
the 1: 50 000 scale map. The root mean square error 
(RMSE) of the position of the newly digitized features was 
1.5 m. At none of the points did the difference exceed 25 m, 
which was the limit set by the map accuracy standards at the 
9096 confidence level. The REMSE of the 1369 feature 
points tested in the 1:10 000 orthoimage was 0.8 m and only 
396 of the points exceeded the 5 m limit set for the 9096 
error. 
The above results are most satisfactory. The map accuracy 
standards are satisfied and the RMSE of digitization in both 
orthoimages has a subpixel accuracy. At the scale of the 
aerial photographs used to form the orthoimages the RMSEs 
correspond to 0.037 mm and 0.023 mm respectively. The 
magnitude of these values is in the range of the measuring 
accuracy attainable in second order photogrammetric 
plotters. 
4. CONCLUSIONS 
All phases of the digital orthoimage generation developed at 
UNB are performed in a GIS environment, which has been 
equipped with both vector graphics and raster image 
handling capability. This scheme is especially attractive for 
resource mapping and map revision since the orthoimages 
can be formed on as needed bases. GCPs, needed for the 
geometric transformation, can be selected interactively in the 
same environment, in a symultaneous dispay of a map and 
image. In the map revision experiment conducted with digital 
orthoimages, a low cost document scanner was employed to 
digitize the photographs. Nevertheless, the map accuracy 
standards were fully satisfied, which indicates, that the low- 
cost digital orthoimage production schem presented here has 
a definite merit. More experiments are, however, needed to 
evaluate the full potential of this scheme and to refine the 
methodology. 
ACKNOWLEDGEMENT 
This development work was funded under the Canada/New 
Brunswick Subsidiary Agreement on Industrial Innovation 
and Technology Development. 
REFERENCES 
Boniface, P.R.J., 1992. PRI2SM - Softcopy Production of 
Orthophotos and DEM. Photogrammetric Engineering and 
Remote Sensing, 58(1): 91-94. 
Derenyi, E.E. 1991. Design and Development of a 
Heterogeneous GIS.CISM Journal ACGC, 45 (4): 561-567. 
Drummond, J., M. Rosma, 1989. A Review of Low-cost 
Scanners. International Journal of Geographical Information 
Systems, 3(1): 83-95. 
223 
Hummer-Miller, S., 1989. A Digital Mosaicking Algorithm 
Allowing for an Irregular Join "Line". Photogrammetric 
Engineering and Remote Sensing, 55(1): 43-47. 
Mayr, W., and Heipke, C., 1988. A Contribution to Digital 
Orthophoto Generation. International Archives of 
Photogrammetry and Remote Sensing, 27(B11): 430-439. 
Mueller, W., and H. Sauleda, 1988. Orthophoto Production 
in the New Context MAPPER system. International 
Archives of Photogrammetry and Remote Sensing, 27(B9: 
II224-233. 
Skalet, C.D, G.Y.G. Lee, and L.J. Ladner, 1992. 
Implementation of Softcopy Photogrammetric Workstations 
at the U.S. Geological Survey. Photogrammetric 
Engineering and Remote Sensing, 58(1): 57-63.