t Photogrammetric triangulation with the aid of geodimetermeasured 
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pases or polygons 
551 Introduction 
The demand for lage-scale (1 : 1,000, 1: 2,000, | : 4,000, 1 : 5,000) basic maps 
or technical projecting has greatly increased of late, particularly with regard to 
Northern Sweden where extensive watercourse regulations and power station 
installations are always under way. In these regions the geodetic network is very 
sare and large areas are entirely without a modern geodetic control net. The 
mature of the ground makes transport difficult and ways of communication are 
sparse, for which reason geodetic measurements are tedious and expensive. A 
method has been developed to map these regions photogrammetrically with suffi- 
dent accuracy without the aid of other quantities than bases and height control 
points. It is of minor importance that maps of this kind are made in a given 
sodetic co-ordinate system. The main thing is that the scale of the map is de- 
temined with sufficient accuracy. The demands as to the accuracy of the contour 
lines for the maps we are concerned with here are, as a rule, so great that the 
miantation must be based on at least four height control points in each stereo- 
sopic model. It is then natural to utilize these height control points required 
for the construction of the contour lines to increase the accuracy of the plani- 
metric triangulation. In this way the "principle of model triangulation" has been 
evolved — a method to determine planimetric control points that has been used 
by RAK for eight years. The development work has been done in cooperation 
vith Professor Hallert at the Division of Photogrammetry at the Royal Institute 
of Technology. 
f 
52 Principle of method 
The method was published by Ekelund in 1950 and in 1952 (23). The following 
items are essential. 
(I) All models in the strip are oriented in the stereo-plotter in one and the 
same basic position (“base inwards’’), which eliminates certain constant instru- 
ment errors connected with the change between base inwards and base outwards. 
In this way triangulation can also be done advantageously in a stereo-plotter of 
the 2nd order, for instance, the autographs A6 and AS or the Kelsh plotter. 
(2) In each stereoscopic model so many height control points are assumed that 
the model can be levelled. Water surfaces can frequently replace height-determined 
ground points. Triangulation starts with a model whose scale is approximately 
fixed, for instance, through base measuring. 
() Connection points between the models are marked on the negatives or 
diapositives as fine crosses. At each connection three cross points are generally 
sed (see fig. 19). They occur only in the common photograph, for which reason 
the adjustment of the measuring mark must be done monocular. This procedure 
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