- 24 - 
formed at the National Research council of Canada, Photogrammetric Research (Mr. T. Bla- 
chut), however, no particular information was obtained. 
Finland : 
The horizon camera Wild HC1 is presently experimented in connection with Wild Avio- 
gon photography. Tests performed seem to indicate that the accuracy of tilts obtained is excel 
lent. - It is planned to experiment in the future the use of Wild HC1 horizon pictures in connec 
tion with instrumental and analytical aerial triangulation ; also the future use of APR is consi - 
dered. It is felt that this kind of aerial triangulation with auxiliary data would yield sufficient 
accuracy for ground control necessary for the mapping of Northern Finland. - When perfor - 
ming horizon controlled instrumental aerial triangulation (strip triangulation) the first model 
is leveled by using the horizon picture tilts 9 h and co h . In the second model tilts 9' 3 and o' 3 
for the third photograph are obtained by relative orientation. Then the tilts of both photographs 
of the ^second model are given corrections in the stereo instrument : A 9 = -|-(9hg - 9' 3 ) and 
Aw =-^-( w kg - 0)1 g) u. s.f. . It is planned to perform research regarding the proper weighting 
of horizon picture tilts. - For the performance of strip triangulation with horizon pictures an 
average of 8 evenly distributed given and targetted geodetic ground control points per 100 km 2 
are available. Second and third order conformal formulas are applied for the strip adjustment 
of horizontal coordinates using computers IBM 1410, IBM 1620 and Elliot 803, and graphical 
methods for elevation adjustment. Block adjustment for horizontal coordinates is extensively 
performed. - For strip triangulation with horizon pictures Zeiss Topogon RMK H 18/10 came 
ra aerial photography is taken (flight height = 4 600 m, length of strips = 40 km = appr. 13 to 15 
models) and strip triangulation is performed at the Zeiss Stereoplanigraph C5. Standard resi 
dual point errors (\/m 2 + m 2 ) after adjustment of the aerial triangulations are + 40 to 50 mi 
crons reduced to the image y plane ( = 1. 8 to 2. 3 m on ground = 1/2 500. h to 1 /2 000. h, where 
h = flight height). Reference is made to : '' Publication of the Finnish Geodetic Institute № 46", 
pp. 125-143 by K. G. Lôfstrôm. [7] - For these aerial triangulations the instrumental time a- 
mounts to 2. 5 hours per model (recording of 25 points per model) and a computer time of 4 to 
5 minutes per model for the horizontal strip adjustment is necessary. - It is considered that 
horizon controlled aerial triangulation is somewhat less expensive than aerial triangulation wi 
thout auxiliary data, and that for economical reasons the performance of such aerial triangula 
tions is compulsory to provide the necessary ground control for mapping project to minimize 
the time and cost consuming ground surveying. 
France : 
Only the I. G.N. performs aerial triangulation with auxiliary data (statoscope and A. P. 
R. ). For appr. 25 % of all block triangulations statoscope data are used. At present it is not 
considered to use other auxiliary data. - When performing strip triangulation by means of the 
Poivilliers Stereotopographe or analytically with a stereocomparator the vertical angle between 
adjacent air bases is determined using the statoscope altitudes of the corresponding exposure 
stations. During the preliminary adjustment, the value of the longitudinal tilt is obtained by 
least squares adjustment between the statoscopic values and the values given by model-connec 
tion. The final exposure station altitudes are computed as : Statoscope altitude difference (bet 
ween adjacent exposure stations) +Z q +aX. The constants Z Q and " a " are used to take into ac 
count a datum error and the inclination of the isobaric surface resulting in exposure station al 
titude corrections which increase linearly with the distance X from the beginning of the strip . 
Z Q and " a " are determined by a Least Squares adjustment. Reference is made to the commu 
nication of the I. G.N. to the London Congress 1960. - Astronomic and geodetic ground control 
points with an average density of 10 points per l°x I o are used for the horizontal adjustment of 
aerial triangulations with statoscope data. As vertical control for the adjustment of such aerial 
triangulations are used : Precision geodetic leveling points, barometric leveling points, verti - 
cal angle measurements and A. P. R. data. The density of this vertical control is variable but 
it is rëquired that at least three non-colinear vertical control points are available per strip. In 
case of existing tie strips in block triangulations the number of required vertical control can be 
correspondingly decreased. With regard to adjustment procedures used reference is made to