Yuri Knizhnikov 
  
AL 
0 
S 
  
L 
AL, = p | (23) 
Usage of relation (23) will allow to calculate (a priori) value of a threshold of stereoscopic perception of spatial depth 
on a stereo pair of discrete images, which ones will be obtained as a result of analogue-digital conversion, and to 
estimate properties of observed stereomodel. Under the formula (22) it is possible to receive an a posteriori estimation. 
5.3 Experimental interpretation of a forest on discrete aerophotoimages 
The capabilities of extraction of the spatial information on discrete stereoimages were reviewed on an example of the 
digitized aerophotos of a scale 1:1500, obtained by the AFA-BA-40 from an altitude L = 600 m and basis B = 60 m. 
The stereo pairs of d discrete aerial photographs obtained by scanning of initial images on a complex of INTERGRAPH 
and by using of the software package PHOTOSHOP are shown in figure 6. 
Three stereo pairs of discrete images were produced from pixels of the square form by the size 0,3, 0,9 and 1,8 mm. 
According to the formula (16) resolution of discrete images, reduced to the sizes on terrain, have compounded - 0,8, 2,5 
and 5,1 m (produced images were adduced to a scale 1:2000 for convenience of researches). Secondary aspen and birch 
forest by an altitude of 28-30 m is shown on obtained discrete images. Some young arbors by an altitude of 8-10 m 
grow to east from house. 
The stereo pair of discrete images, for which one a threshold of stereoscopic perception of depth (L,), reduced to the 
sizes on terrain, makes 8,4 m (formula 22), is shown in figure 6a. The given stereo pair allows confidently interpreting 
three levels on an altitude: a herbaceous cover, group of young arbors, adult forest. The threshold of stereoscopic 
perception of depth of the second stereo pair (figure @) is equal 25,5 m on terrain. The stereomodel flattens out, and 
only two altitude levels - herbaceous cover and an adult forest are stereoscopically differed on these images. The 
threshold of stereoscopic perception of depth for the third stereo pair (figure 6c) is so great (50,9 m), that the discrete 
stereomodel becomes actually flat. 
The results of stereoscopic recognition of different altitude forest elements, which are shown on three stereo pairs of 
discrete aerial photographs (figure 6), demonstrate, that the offered relation (22) allows to estimate a stereomodel of 
discrete images, sufficiently for prediction of its possibilities for interpretation of investigated objects, and also for 
definition of quality of the spatial information about studied geographic objects. 
Many categories of geographic objects are differed on a relative altitude. The settlements, forest, relief and others are 
concerned to such objects. For interpretation of available altitude differences it is necessary to forecast and to estimate 
properties of stereomodels observed on discrete images, which ones are particular formed by analogue-digital 
conversion of continuous (photographic) images. With usage of offered relations (22) and (23), it is possible to calculate 
the sizes of pixels, and, therefore, parameters of scanning (size of the aperture and sampling rate), which ones provide 
the sure interpretation of available altitude differences. 
6 CONCLUSIONS 
Analog-to-digital (A/D) conversion is one of the basic ways to receive discrete space images for computer-based 
mapping. It is shown that A/D conversion of the continuous (photo) images produces to the losing upon not less than 10 
per cents of the initial cartographic information. It is necessary to take account of this information loss in agreement 
with specific properties of visual interpretation of the discrete space images. 
Notion of integrate object of recognition which is consisted of finite quantity of image pixels was determined. Such 
objects are interpreted as integratedly percepted images. This feature is formulated in gestaltpsychology (from a 
German word Gestalt - integrated object, integrated form). Integratedly percepted images have no an inside structure, 
but their forms are visually percepted as a unit. Diagonal of the area of integratedly interpreted object has compounded 
approximately five-multiple value of the resolution of discrete space images. The following this relationship is 
necessary for sure interpretation of integratedly percepted objects on discrete space images of defined level of 
generalization. 
  
512 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B3. Amsterdam 2000.