Abstract
This paper describes the methods and experiments about automatical height file production and contour drawing from stereo aerial photographs using off-line image correlation. Densitometric data were obtained with a drum scanning micro densitometer and processed by a general purpose computer.
Followings are the scheme of the experiments and some related remarks:
(1) A pair of digital images of stereo aerial photographs were rectified to the equivalent images which have no y-parallaxes. To reconstruct the images nearest neighbour interpolation was used.
(2) The heights at the grid points in the ground coordinate system were sequentially searched to draw contour lines using cross correlation coefficients as a matching criterion. However, for obtaining successful results, some modifications were necessary:
a) Perspective distorsions due to ground reliefs weaken the correlations. The weighted correlation was proved to be effective to moderate this difficulty.
b) For the sequential searching for conjugate image points, close approximation of height values was needed to specify the appropriate search window. This was possible by use of the mean height of neighbouring two points of the concerned grid point as an approximate value.
