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formations, reasonnings and results refer to this pro- 
ject. A supplementary project, however, is carried 
through in 1961, and when referring to this one it 
will be mentioned. 
The area for this second test project is named 
Radoy, which is an island situated at the west coast 
of the country. The terrain here is without forest, 
and consists of moors, heathery hills and naked rocks, 
and is typical for the coastal area and may also in 
some respect represent the area above the forest 
limit in other parts of the country. 
Here is only used the photoscale 1: 15000 VA, 
and the control coordinates for all points (nearly 
200) are terrestrially measured. Two of the field 
operators from the first project have each recorded 
about all the points. The restitution work is done bv 
different stereo operators in the two projects. 
STEPS OF THE FIELDWORK 
Terrestrial passpoints 
To procure passpoints for all the stereo models, 
the 6 models of a photography in scale 1 : 25 000 
were provided with terrestrially measured passpoints. 
Out of these models the control for all the 76 others 
was photogrammetrically measured. 
To get the best possible passpoints for the control 
series, signals were distributed before photography 
to possible places along the sides of the planned 
strips. This work proved to be most worthwhile. 
Signalizing of boundary points 
This work was here performed by technicians, the 
field operators which later did the identification of 
the points in the photographs. 
The dimension of the signals was mostly 90 X 90 
cm, and either made of sheets of plastic or cotton- 
cloth, or latexpaint. Both white and yellow colour 
was used. The paint was most handy when naked 
stone could be used as base for the signal. 
In other cases the sheets could be laid directly on 
the ground, fixed by some heavy stones. In forest, 
however, was it usually necessary to get the signals 
raised from the ground. The sheets had then to be 
stretched over a cross of wooden laths and fixed above 
the cut off top of a tree, or to the top of a stake. 
All boundary corner points should be signalized, 
preferably in the point itself, or when this is con- 
venient, besides and as near as possible. 
For continuous natural boundaries signals were 
placed with regular intervals. 
Identifying and marking the points in the photographs 
The test area was sheared between three field 
operators, and within each part the one operator did 
the identification work with the four different series 
of photography, in different sequence for each of 
them. 
The manner of proceeding is fundamentally the 
same for the series with signalized points as for the 
ones without, and is previously explained under the 
description of method b). 
Within the area about 1400 points were signalized. 
In spite of the work being relatively well done, only 
950 of the signals were visible in one or both photo- 
graphs of the stereopair. 
Supplementary to the work with the regular four 
unsignalized series, some special tests were performed, 
e.g. with two or more operators identifying the same 
points in the same photographs, always pricking the 
boundary point without regard to visible detail or 
not, or using half-transparent plastic base for the 
photographs. 
By asking the field-operators they all agreed in 
preferring the normal angle photography in scale 
1 : 15 000, because of being the easier one for identi- 
fying the points. The reason should be the less radial 
distortions caused by height differences, compared 
with wide angle. About the different scales of the 
wide angle photography the agreement was not so 
strong, but with probable preference of the scale 
1:15000. 1:20000 was considered most difficult, 
and the main advantage of the 1: 10 000 photographs 
was said to be the more space for pricks, connection 
lines and numbers. 
ACCURACY OF COORDINATES OF THE 
CONTROL POINTS 
The accuracy of mapping signalized points is not 
the aim of this investigation, but as they are serving 
as control for the unsignalized series, the magnitude 
of the errors have to be known. 
The standard deviation computed from differences 
between several independent photogrammetric deter- 
minations of signalized points, combined with the 
planimetric error of the absolute orientation of these