48 
  
NE QUADRANT 
  
HT TERRAIN 
! | | DATA POINTS 
|| 
i 3 
| nN SHORT DIAGONAL 
P d 
T ^ mas 
| 
SW QUADRANT SE QUADRANT 
  
  
  
  
  
  
Fig 9. Elevation Determination of Single Point 
The length of the two diagonals between the four points is com- 
puted to configure the two triangles that will have a common side, 
the shortest diagonal. 
The triangle which includes the starting point of the profile is 
determined. Using the three spatial coordinates of that triangle, 
the equation of the plane so generated is computed after which 
the elevation of the coordinate at the beginning of the profile 
line is computed. Note that the original "criterias" for terrain 
data points has not been violated. 
Now that the elevation of the first point is determined, the pro- 
cedure changes. By using an equation for a line to line intersec- 
tion, the coordinate for the intersection of the profile line and 
one of the lines connecting the four terrain data points, can be 
determined. Knowing the coordinate of the intersection, the eleva- 
tion of that intersection is determined by proportion from the ele- 
vations of the two terrain data points. 
The computed spatial coordinates for the intersection is stored and 
the four closest terrain data points around it are again found in 
each of the four quadrants. Again the line to line intersection tech- 
niques is applied, a spatial coordinate computed, stored away, the 
procedure repeated until the end of the line is reached. The proce- 
dure for determining the elevation of the last point is the same as 
that used to determine the elevation of the first point. Again note 
that the criteria for the terrain data points has not been violated. 
  
All o 
one t 
one t 
sects 
here 
the t 
econo 
time. 
One p 
phic 1 
velop 
ever, 
A spa 
velop 
tive ( 
and at 
map. 
This 
tive. 
plans 
plans 
The FL 
  
It see 
to the 
stay. 
abilit 
It may 
gramme 
prov id 
know t 
DTM me