AZgr=(AZy+AZz+AZz+AZ2,):4 - height of prism above hori- 
zontal plane. 
In the second case, the area p located inside polygon is 
multiplied by prism height, calculated as given above and 
V=p AZsr 
Total volume per section is obtained through adding volumes 
from particular meshes,and for the whole object individual 
sections are summed up. 
Influence of height errors on accuracy of volume determina- 
tion for 1 ha can be estimated as follows: 
dV210000 s - systematic deviation influence 
mV= 400 m - random error influence. 
As can be seen, systematic deviation has the principal 
influence on determined volume. Therefore it is better to 
calculate volume increase at a certain period /usually 
annually/. Then, using similar aerial photographs, impact 
of systematic deviation is reduced and accuracy increases. 
During implementation of the described method in survey 
ing enterprises, comparison with the earlier used methods 
was performed. In the State Enterprise of Geodesy and 
Cartography in Warsaw volume of the reservoir of flotating 
muck was determined, using method described by S. Dmocho- 
wski and R. Butowtt in the article:'Determination of volu- 
me of materials deposited in sedimentary reservoirs', and 
using above described method. The corresponding volumes 
were: 
in first case 2 14.960 180 m 
in second case -.15:132.245 m 
The difference was 172 065 m, which ts about 1,15 % of 
determined volume. 
Volume of phosphogypsum dump determined by Gdansk Regional 
Enterprise of Geodesy and Cartography, was calculated 
multiplying area by mean height taken from height map. 
The following magnitudes were obtained: 
- on the basis of the map - 475 750 m 
- on the basis of DTU = 153 732 m 
so the difference was only 2.01 . 
- 207 -