4] 
  
  
Polygon Number of Total distance Closur error 
n:o lengths meters meters 
1 3 38.817.96 0.34 
2 5 50.986.21 0.21 
3 8 65.139.38 0.24 
4 3 31.204.62 0.02 
5 10 117.186.71 0.47 
6 3 33.849.78 0.14 
7 4 49.085.63 0.20 
8 4 47.413.68 0.41 
9 5 59.364.37 0.29 
Fig. 2. Geodimeter net — Luleà River. 
These stations are widely-spaced in the highlands of northern Sweden, 
and therefore the Power Board network does not have many tie-ins to 
existing controls. Fig. 2 shows the errors of closure obtained for the 
Luleà River network. The distances were measured with the NASM-3 
geodimeter, which has proved itself a precision instrument which is 
suitable for field conditions. Our experience shows that the error in 
distance measurements may be computed as == 6 7X 10 5x s m (where 
s is the distance measured). In addition, when the geodimeter is used 
we have found that any distance assessible to measurement will be 
measured correctly within the limits stated in 99 cases out of 100. 
The sides in the polygonal net were made 8 to 12 km. This length was 
selected for the following reasons: 
1. The control points thus established are to serve as stations in subs- 
equent photogrammetric triangulation. It was the intention to avoid 
having to triangulate more than four models or so. 
2. Reconnaissance and measurement takes much less time than of 
longer lines had been run. This is a very important factor when it 
is desirable to establish control points rapidly. 
3. The control points will also serve as the staring points for subs- 
equent geodetic surveys at dam sites and the like. It is therefore 
desirable that they be located near watercourses in order to avoid 
the necessity of excessivley long and difficult tie-in measurements. 
Station marking 
As the foregoing account has made clear, our base mapping has a 
relatively sparse network of horizontal control points. As a rule, these 
stations are marked before the strips is flown. In the terrain in 
question, there is so little detail suitable for use as reference that the 
identification of stations on the photographs is difficult. The markers 
are usually made of sheet plastic weighted with stones or anchored with 
chicken wire. The marker is made about 1/10000 the scale of the photo- 
0