TS 
  
As most engineering projects relating to the shape of the earth 
usually require profiles, the methods used in generating these 
profiles from a DTM will be reviewed here. Keep in mind that the 
terrain data being used is obtained along terrain break lines. 
The computer algorithms are designed to use such data. 
The selected is bounded with coordinate limits to form a rectangle 
which is further divided into blocks. Each of these blocks should 
contain at least one and not more than 50 data points. All of the 
terrain data points are then sorted into their appropriate blocks. 
See Fig 7. 
The line along which a profile is needed is defined by coordinates, 
one at each end. The elevation of the starting point of that line 
1s determined as follows. 
  
  
  
  
  
  
BLOCK SIZE 
  
  
  
  
  
  
  
  
  
$ e e ; o 3 a 
DTM : 
INTERPOLATED : 
POINTS : 
STARTING : 
MOORDINATE 2 . : . 
$ . . x e 
Fig 8. Generation of Profiles BLOCK SIZE 
Note that the 9 blocks of data surrounding that first point are 
brought in from random access storage and are stored in core for 
ready use. 
0 The closest terrain data point in each of the four quadrants sur- 
rounding the coordinate at the beginning of the line is found and 
stored. See Fig 9. 
  
47 
TERRAIN 
DATA 
END 
COORDINATE