Finland
of Zeiss cameras RMK HS 21/18 x 18 (Orthometar), RMK HS 10/18 X 18 (Topogon),
RMK 21/18 x 18 (Topar) and others, Zeiss stereoplanigraphs C5, Wild autographs A7
and A8, Zeiss Multiplex and Stereotop instruments etc. Among the rectifiers Zeiss SEG V
takes the first place.
The aerial photography is carried out by the Air Forces, according to plans and using
cameras and other equipment placed at their disposal by these two offices. Processing and
further treatment of the aerial films as well as the organization of the picture archives is done
by them too. Two Percival Pembroke survey air planes were purchased by the General
Survey Office to be used for aerial photography by the Air Forces.
In addition to ordinary mapping the mentioned instances prepare various aerial mapping
works for other government establishments, towns and private undertakings. Pictures are
delivered also for communal tax equalization surveys, geological surveys, forestry work, for
planning of power plants etc.
The Chart Section of the Board of Navigation prepares nautical charts, including inland
water charts with the aid of photomaps. The Decca navigation system is also used in the
echo sounding on the Gulf of Bothnia.
More than 30 000 km 1 2 are yearly photographed for different purposes and the total area
covered by air pictures is now about 289000 km 2 or 86 % of the total area of Finland.
Special photogrammetric methods and investigations.
The component angles of tilt of the aerial camera are in Finland determined by
the horizon method 1 2 The relative component angles are measured from the two horizon
pictures with a mean error of about 2',5 (centesimal minutes). 4
For stereotriangulation purposes two pairs of pictures in every strip of 15 to 20 pictures
are absolutely orientated in the stereoplanigraph using ground control. With the obtained
correction angles the absolute components of tilt for the whole strip are calculated. The
obtained mean error of the latter ones is about ^ 4',o for the longitudinal and ^ 2/7 for the
lateral tilt.
Horizon controlled stereotriangulation 2 is used to obtain hori
zontal and vertical control for stereoplotting of a map 1 : 100 000 in Multiplex. With a
wide angle camera f = 10 cm, flying height 4000 m the photography is performed at the
scale 1 : 40 000. The length of the strips is 40 km and ground control is established in distances
of about 20 km in each strip. The essence of the stereotriangulation applied here is that every
stereomodel is levelled in the stereoplanigraph according to the predetermined absolute
components of tilt.
For checking of the accuracy of this kind of stereotriangulation, points of horizontal control
were measured in distances of about 4 km and along the edges of two test strips, vertical
control was levelled in the field. The results have proved that the accuracy obtained (mean
square error m x = rriy = -j- 3,0 m and m^ 2,1 m) is satisfactory for the purpose in question.
The practical works carried out until now (about 500 pictures) have shown the stabilizing
1 influence of predetermined tilt components for the stereotriangulation. The mean square
error of the extended net of horizontal and vertical control obtained in the conditions men
tioned above are m x — m y = j; 3 to 4 m and /«h = ¿2 to 2,5 m.
Substitution of scale check lines by vertical control is a new
method for determination of the enlarging ratio 3 of each air picture in the rectifier. Until
1 Löfström, K.: Die letzen Fortschritte in der Horizont- und Statoskopvermessung. Schwei
zerische ZfV., 1946: 7.
2 Löfström, K. G.: Horizontkontrollierte Aeropolygonierung. Veröff. des finnischen Geod.
Institutes, N:o 46, S. 125—143, Helsinki, 1955.
3 Laurila, Simo: Applied scale point method in Finnish practice. Photogrammetria, 1949
~^5° : 3-
4 R. S. H a 1 o n e n: Über die Genauigkeit der Methoden zur Bestimmung der äusseren Orien
tierungsgrössen der Luftkammer. Dissertat. T. H. Helsinki, 1951.
