BASIC GEODETIC CONTROL 
  
The unexplored areas very often lack basic geodetic 
control. A basic geodetic network must be established as a 
first step in any survey and mapping program. The Aerodist 
has proven to be an excellent tool for establishing of first 
order geodetic control by employing trilateration methods. 
The basic geometric figure in the trilateration network is 
a quadrilateral. In order to obtain a high degree of accuracy 
it is recommended that a system of double-braced overlapping 
quadrilaterals be used (See Fig. 2). All distances in a 
trilateration net are measured employing the line crossing 
procedure (Fig. 3). The distances a and b are simultaneously 
measured and are separately recorded. The distance between 
points A and B equals the sum of a * b when a+b = minimum. e 9 
The results obtained with the Aerodist proves that distances 
can be measured in this way with an accuracy of 1/100,000 and 
better. Recently, a geodetic network was established in Guyana 
by Terra Surveys Limited using Aerodist. The final adjustment 
indicates an accuracy approaching 1/200,000. 
SECONDARY HORIZONTAL CONTROL 
  
The secondary horizontal control is established by 
means of Aerodist-controlled photography. During a survey