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partly permanent. High-altitude-photography (e.g. 1:40 000) over group-area 
and low-altitude-photography (e.g. 1: 4 000—1: 10 000) over station-areas. Signals 
identified partly from helicopter or aeroplane. 
Photographs (enlargements, stereo-pairs) are immediately used as maps during 
preliminary ground investigation, for location of seismic profiles, diamond 
drillings etc. 
Stereotriangulation in A7 of high-altitude-strips, scaled on ice-bases, balanced 
on lakes and with azimuth from sun-observations. In the meantime urgent pro 
jects preliminarily studied in rough Kelsh-models. An approximate reconnais 
sance map plotted in A6 and Kelsh in 1:10 000 with 5-meter-contours for general 
planning, calculation of preliminary reservoir-volumes etc. 
Stereotriangulation of low-altitude strips over most probable projects, now 
perhaps only half of the photographed »station-areas», scaled on signals deter 
mined in high-altitude triangulation but horizontalized on rather sparse ter 
restrial levelling. Approximately 50 % of the area of each remaining »station- 
area» is plotted in 1:2 000 with 1-meter-contours after a photo-geological study. 
Projects have now crystallized which decrease the need for general maps 
(1:10 000) and large scale maps to e.g. 30 % and 15 % of total photographed 
area respectively. Further terrestrial levelling facilitates the horizontalizing of 
plotting-models for 1:10 000 maps and large-scale-maps. Terrestrial geodetic 
control nets covering remaining parts of station-areas give accurate scale for 
repeated large-scale-plotting of final construction maps, now in e.g. scale 1:1 000 
with 1-or 0.5-meter contours with coordinate systems oriented parallel to that 
of the high-altitude-triangulation. 
The method briefly described above, gives without great delay the material 
the projecting engineer needs. The expensive and timeconsuming terrestrial con 
trol-survey and accurate stereo-plotting is limited almost exclusively to areas 
of interest for the final projects. 
Photogrammétrie par degrés pour les projets hydro-électriques 
Supposé que plusieurs constructions alternatives sont faisables dans un vaste terrain, partiellement 
rempli de lacs utilisables comme réservoirs. 
Le terrain entier est photographié à haute altitude et les parties probables pour constructions, à 
basse altitude. 
Stéréotriangulation et restitution approximative de la majeure partie des photos aériennes 
donnent la possibilité de choisir entre les différentes alternatives. Là-dessus une restitution de 
précision d’une partie limitée (30 %—15 %) donne les levers nécessaires pour les constructions 
et les bâtiments. 
Par cette méthode, qui est mise en pratique à la Direction de l’Energie Electrique de l’Etat 
Suédois, l’ingénieur-projecteur peut recevoir rapidement une base pour son travail. Le lever de 
précision, coûteux et retardant, de vastes terrains qui n’ont pas d’intérêt pour le travail définitif, 
est évité. 
The floor was given to Mr. G. C. Tewinkel (USA), who gave a lecture on 
»Hydrographic Application of Photogrammetry in the U.S. Coast and 
Geodetic Survey». Summary: 
Photogrammétrie techniques and products are employed extensively by the 
United States Coast and Geodetic Survey in connection with hydrographic sur 
veying for the publication and revision of nautical charts of the coastline of the 
nation and its territories. Planetable surveys which were used formerly to 
establish hydrographic control and to traverse the shoreline have virtually been 
replaced by photogrammétrie surveys. In certain instances the photogrammétrie 
surveys may precede the geodetic control phase. An important application lies in 
the establishment of control points by means of photogrammetry for subsequent 
use during the hydrographic survey. 
Charts are revised by means of special aerial photography and photogram- 
metric techniques. A small airplane is used to obtain low-altitude photographs 
G. C. Tewinkel: Hydro- 
graphic Application of 
Photogrammetry in the 
U.S. Coast and 
Geodetic Survey. 
(Publ. IV T 1)