rth exercises a much
» refraction. Basically
on, since if the model
ch are free of all er-
terrain including its
1. Nevertheless, the
a model which is
This can be achieved
; in height between
lane tangential to it
| picture. The “dis-
rtional to the flight
1e third power of the
otationally symmetri-
photography, and for
ed for, together with
> of correction plates
cal purposes both re-
re are taken together
n.
from earth curvature
rder of 10 to 100 mi-
ected for during plot-
in asking for survey
a few microns.
esults of Practical In-
iracy of Aerial and
ciples have been ap-
s, micro photographs
aphs from terrestrial
ilar tests than have
ngress have been per-
es, but unfortunately
d instead I have here
:h can be distributed
interested.
tioned that a clear
photographs has been
Is the standard errors
n the centre is larger
f points in the centre.
ild take into account
in the photographs at
; of a theoretical na-
call it the Y-parallax
plied for routine tests
Jlotting. Good results
this method under
re 1 will refer to the
n IV-4, in particular
material from Sub-
Commission IV—3, the Canada Commission.
Finally, since there is evidently some mis-
understanding concerning the quality of the
Y-parallax method, I will quote some senten-
ces here from the paper, *The Grid Method
and the Y-Parallax Method for the Determi-
nation of Systematic Disturbances in Aerial
and Terrestrial Photographs.” This paper was
presented to the Stockholm Congress in 1956,
and there the Y-parallax method was first pu-
blished. I quote, on page 14, as follows:
*Finally, it has to be emphasised that a
grid method gives more accurate and com-
plete information about the systematic dis-
turbances than the Y-parallax method. The
latter method is particularly limited by the
considerable correlation between the two
pictures. There may be distortion effects in
the two pictures that cannot be distiguished
from each other in this way. Neither of the
two methods can give any absolute deter-
mination of the elements of the inner orienta-
tion under here assumed conditions."
This means that those methods are to be
used only for the determination of what we call
non-projective errors, in other words errors
that cannot be compensated with the elements
of relative or other orientation.
It seems to me to be most important that we
should try to determine the irregular variations
of these non-projective errors and this can be
done I think only in utmost convenience with
the aid of a grid test field on the ground. Then
we can determine from day to day what va-
riations may be caused, for instance, by the at-
mospheric reflection.
Prof Hallert then showed two slides. The
first slide was an example of the examination of
radial distortion from Y-parallaxes only in
connection with contour tests. The second one
showed the test from the air of a certain photo-
graph over the test area in Sweden. Prof Hal-
lert then said:
We have also determined a standard area of
unit weight of each of these circles along which
we have determined the distortion, and as I
said, there is a clear increase of the standard
error within the distance from the centre, in-
dicating the points located far out along the
edges have a lower weight than the points which
are in the centre of the photograph.
Dr P. THAM: In Liberia, the Company LAM-
BO, which means the Liberian American Swe-
dish Mineral Company, in a joint venture with
the Bethlem Steel Company, has had to carry
GEOMETRISCHE EIGENSCHAFTEN DES BILDES, DISCUSSION 55
out geometric and photogrammetric measure-
ments in order to establish maps for a mining
project of important magnitude. There are spe-
cially two kinds of experiences collected from
this work; from the photographic point of view
the unavoidable necessity of using an infra ma-
terial, thus giving interesting experiences; from
a photogrammetric point of view this material
has required a close study of the relation be-
tween the vertical parallaxes, the lens distortion
and the stereoscopical model.
The last mapping experiences can be read in
my Congress paper entitled “Vertical Paral-
laxes, Lens Distortion and Stereoscopical Mo-
dels". Concerning the problem of the vertical
parallaxes, this paper should perhaps belong
to Commission II, but as to the lens distortion
problem, it seems to be discussed in this Com-
mission. I guess that very few Congressists have
seen this paper yet, therefore I will shortly give
the ideas behind the paper.
In this stereo instrument, the lens distortion
curve corresponds to an original position of the
stereoscopical picture, that means the original
position which with any arbitrary point will
give the exact horizontal and vertical parallaxes
of that corresponding to the lens distortion in
that point. I record this position for the theor-
etical position. However, the instrument operator
is never aware of this theoretical zero position,
he only observes the existing parallaxes in the
orientation points of the x-point scheme. This
aim will be to reduce them by means of tilting
the element to such a small amount as he can.
But the insertion of the tilt will result in a mo-
del deformation too, of course.
A theoretical treatment of this fundamental
problem establishes that the residual vertical par-
alaxes alone cannot give any information of the
lens distortion curve a they represent a disturbed
zero position of the stereoscopic picture. It may
be added that thanks to these experiences the
map collecting in Liberia has been carried out
sucessfully up to now. I do not like to talk much
about my paper as you can read it.
I would only like to emphasise three points.
Firstly, it must evidently be established that
basically any related orientation with pair
stereoscopic pictures will represent in a dis-
turbed zero position, therefore it must be con-
sidered as impossible to derive the lens dis-
tortion from the regular vertical parallaxes only.
These parallaxes have a very problematical rela-
tion, if any, to the lens distortion curve.
Secondly, in addition to my paper, Profes-
sor Hallert has made some notes. From these
notes I would like to read only three lines:
