You are using an outdated browser that does not fully support the intranda viewer.
As a result, some pages may not be displayed correctly.

We recommend you use one of the following browsers:

Full text

Remote sensing for resources development and environmental management
Damen, M. C. J.

Symposium on Remote Sensing for Resources Development and Environmental Management / Enschede / August 1986
New approach to semi-automatically generate digital elevation data
by using a vidicon camera
C.C.Lin, A.J.Chen & D.C.Chem
Center for Space and Remote Sensing Research, National Central University, Chung-li, Taiwan
ABSTRACT: A systematic procedure is proposed for semi-automatic digitization of topographic maps by using an
interactive image processing system, including a vidicor camera. The required input is line-drawn contour map.
A contour-line image is then generated by the vidicon camera. To produce a clean contour-line image with one
pixel in width, standard preprocessing techiniques are adopted, such as image enhancement, noise-removal, line
thinning, and editing etc. The resels and their corresponding boundaries are labeled automatically. Isolated
peaks, flat ridges or troughes, are, then, added afterwards. A look-up table is manually generated,
associating the elevation data with those points, lines or closed boundaries. The elevation value at a given
pixel within a resel is weighted by the two smallest "effective distances" from this point to all of its
neighbors, such as isolated points, lines or boundaries. The effective distance, defined here, represents a
shortest distance between a point and a curve with the connecting path lying within a resel, i.e., the
intersection with the contour lines are not permitted. A,fast computing algorithm is developed to calculate
the effective distances of all the pixels within a resel. The construction of a digital elevation model is
easily achieved. The main advantages of our approach are two-folds. Firstly, the variation of the elevation
values within a resel is well behaved, regardless the complexity of a resel, even for elongated kindly shape,
etc. Secondly, the ridges and troughes are automatically generated and clearly repersented. A simulated
results will be presented to illustrate the processes and demonstrate its advantages.
1. Introduction:
Topographic data are nowadays most commonly
obtained through the technique of comparing optically
photographed stereo pairs of imagery. Large amount
of manpower is needed for applying this method.
However, owing to its great importance, contour maps
are prepared with various degrees of accuracy for
most parts of the world with this or other less
efficient methods.
Satellite images, so far, are not suitable for
extracting precise topographic information(Mckeown,
1984). Yet for many geological, hydrological,
forestry or enviromental applications, it is
necessary to have the digital elevation model (DEM)
(Ragan 1975, 1978). The DEM, thus, also constitutes
an indispensable layer for constructing geographic
information system(GIS) (Ragan et al., 1976; Colwell,
1983; Faintich, 1984).
Interpolation methods have been used to generate
DEM (Tempfli, 1977; Grimson, 1981; Sincar et
al,1984). One of the approaches is that, based on
the given elevation values of some points the
elevation values of other points in a region are
interpolated (Rioley, 1981). Softwares using this
approach are available commercially (SACM, 1981).
Recently, raster scanning system, such as vidicon
camera, becomes more widely available. With the aid
of such system, we can use the contour line map, in
raster format, as the basis of the interpolation. In
a recent article, Sircar and Ragan (1985) described
such a interpolation process, with a method of
steepest decending and 4 reference lines. And it is
adaptable to the small users who need to obtain a
reasonable accurate DEM in a short period of time.
This process, though efficient, cannot spread the
elevation information uniformly in certain types of
terrains, e.g., in an elongated kidney-shaped trough,
the. elevation information in one end of the trough
may not be conveyed to the other end. Nevertheless,
such types of terrains are frequently encountered in
a mountainous area where DEM is particularly useful.
An algorithm that is capable of spreading the
elevation information uniformly in any type of
terrain is presented in this paper. The algorithm is
also suitable for small user to generate DEM quickly.
In section 2.-, prepossessing of the contour line
image is discussed. In section 37 , effective
distance within a resel is defined. In Sesction 4.,
a fast algorithm is devised for finding the
interpolated elevation values. In section 5., an
application example is presented. Finally,
concluding discussions are offered in section 6V.
2. Digitized Contour Line Image and Preprocessing
The image produced by a vidicon camera from a
contour line map, e.g., the line-drawn map shown in
Fig.l, usually has some defects. Hence some
preprocessings are always necessary. The purpose of
Fig. 1. The line-drawn map copied from topomap.