previously). The
altimetric plane,
efers to the plani-
| of altimetric SD
is done by relying
). A function that
stric plane to the
y the interpolation
n”/ A” position” is
SD to a planimet-
> gradient for each
es are generated.
rances is done by
5 illustrates those
j).
| SD buffers
The generated buffers are not uniform in shape
or characteristics. A comparison to buffers that
would have been generated by direct photo-
grammetric contours extraction, where buffers
would have follow parallelly the contours, em-
phasizes this aspect. Figures 5,6 illustrate the
relief shape effect on the buffers characteristics.
Figure 6a represents a window that was ex-
tracted from Figure 5, where the terrain is
characterized by a sharp slope. The buffers
edges are parallel and relatively close to the
contours path. Those characteristics are ex-
plained by: the sharp slope that turns large dif-
ferences in elevation to small differences in
position, and the negligible effect of slope
variation explain the edges parallel shape. Fig-
ure 6b represents ,on the contrary, a window
where the terrain is characterized by a low
slope. The buffers in this case are wider than
those of figure 6a and their edges are more
sensitive to slope variation. The shape varia-
tion's effect is well demonstrated by the curve
that occurs on the left contour that is vanish in
buffer shape.
6. CONCLUDING REMARKS
A method to evaluate accuracy of objects
and spatial applications was presented. The
method that is based on error propagation
techniques enables the precise determination of
standard deviation of elements collected pho-
togrammetrically. Although its mathematical
complexity, the method can be easily imple-
mented within GIS databases and might help
the precise evaluation of spatial data and spatial
analysis.
7. REFERENCES
American Society of Photogrammetry, 1980.
Manual of Photogrammetry. 4th edition.
American Society of Photogrammetry, Falls
Church Virginia. pp. 37-102.
Moffit, F.H. and Mikhail, E. M., 1980. Photo-
grammetry. 3rd edition. Harper & Row, Inc.,
New York. 647 pages.
17
David, M., Theobald, "Accuracy and bias issues
in surface representation”, in (eds.) Goodchild,
M. and Gopal, S., 1989. Accuracy of spatial
databases, Taylor & Francis, London, pp.
99-107.
Zhilin Li, 1993. Mathematical models of the
accuracy of digital terrain model surfaces line-
arly constructed from square grid data, Photo-
grammetric Record, Vol. 14 No. 82: pp.
661-673.
Zhilin Li, 1993. Theoretical models of the ac-
curacy of digital terrain model: an evaluation
and some observations, Photogrammetric Rec-
ord, Vol. 14, No. 82, pp. 651-660.
Torlegard, K., A. Ostman, and Lindgren, R.,
1986. À comparative test of photogrammetri-
cally sampled digital elevation model, Photo-
grammetria, Vol. 41, No. 1, pp. 1-16.
