quate covering of the strips of terrain in question. In Sweden the photo- 
graphy is done by the Geographical Survey Office or Airborne Mapp- 
ing, both of which enterprises have Aviogon cameras RC5 at their dis- 
position. With these cameras the cruising altitude chosen gives a scale 
of approx. 1:13000—1: 15000. 
Before the photographing a network of reference points in the form 
of a polygon system with sides of about 1—3 km is reconnoitered and 
signalled. This polygon system is reconnoitered to be connected up with 
the national triangulation net where it is possible. 
The length-measurement is performed with the help of a tellurome- 
ter, an instrument that works with ultra-short radio waves, and the go- 
niometry is done with a theodolite. Our experience from these measure- 
ments to date shows that the point-accuracy is quite comparable with 
that obtained in triangulation, For the measurement of the points of 
reference for these long and narrow strips here in question polygon 
measurement is clearly superior to triangulation from the viewpoint of 
time, thanks to the possibilities of quick and accurate length-measuring 
afforded by the tellurometer. 
The closing error radially in the polygon system has on an average 
amounted to 0.15 m per 10.000 m. 
Where it has been possible to carry the localization stage to the point 
at which the road-line 1s roughly localized before the photographing, a 
polygon system is in principle reconnoitered along the same and signall- 
ed. This polygon system, whose sides measure approx. 200 m, is intend- 
ed to be used for the staking out of the road, and the coordinates of the 
polygon points are in the image material determined by photogrammet- 
ric triangulation. The necessary calculations for the transformation of 
the photogrammetric model-coordinates to ground-coordinates are made 
with the help of the electronic data machine Facit EDB. The coordina- 
tes of the polygon points are obtained with a standard error of 0.2—0.3 
m in the horizontal plane. 
In the treatment of the road project in these pictures the combination 
of mirror stereoscope and Balplex Plotter (see fig. 4) has proved 
extremely favourable. 
On the tracing table of the Balplex only a limited part of the model 
as large as the surface of the table, 1. e. about 80 cm?, can be viewed 
stereoscopically at onetime but by raising the drawing table to a middle 
height for the model it is possible to view the entire model stereoscopi- 
cally in one look, i. e. the survey of the terrain which is so valuable for 
the road-planner at the stage of the preliminary planning work is ob- 
tained. 
The instrument permits of the simultaneous treatment of 3 models, 
which with pictures on the scale of 1:15000 and map-scale 1:4000 cov- 
ers an area of approx. 4.5 km X2.5 km. 
[n principle, the planning of the road takes place as follows. After