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UFU —————- 
  
  
RADIAL TRIANGULATION, DISCUSSION 87 
be taken into account also in connection with 
investigations of the quality of radial triangula- 
tion. 
Mr P. O. FAGERHOLM: I have been asked to 
join this panel on radial triangulation and have 
taken some interest in the matter, and therefore 
perhaps I should spend just a few minutes on 
it because there has been a lack of time for this 
panel to co-ordinate its ideas. Professor Roelofs 
has said part of what I intended to say, and that 
is fine. 
What I would like to underline especially is 
the need to avoid over-estimation of the draw- 
backs, that radial triangulation only gives the 
x and y co-ordinates, the planimetry. 
What I would like especially to say is that if 
you only have one series of photography from 
one height, you must choose that flying height 
so that in the plotting stage you get the accuracy 
you wish in the final map. If you then have to 
take away a part of the margin for spatial trian- 
gulation this has a pretty great influence in many 
cases on the densening of the geodetic net with 
photographic methods. This, compared with the 
latest developments in radar profiling and good 
barometric levelling in helicopters, etc, is 
changing the entire picture and I think we 
should realise that in our discussions very 
clearly. 
Another good thing with radial triangulation 
is that if it is numerical or mechanical it can be 
broken down in small pieces, and every one of 
these procedures can be checked, either spot 
checked or checked to see if something is going 
wrong in the adjustment if one believes that 
there is something wrong there. That is not so 
easy with spatial triangulation. Professor 
Roelofs mentioned that it is possible, and cer- 
tainly it is true with a horizon method, and so 
on, to determine the nadir distance pretty well. 
That is certainly true. 
I also wish to underline the fact there is no 
need to know the nadir point very accurately 
with the very limited nadir distances we usually 
have in modern photography. 
Something else I should especially like to 
point out is that radial triangulation has a very 
low requirement on the distribution of geodetic 
control points, especially if it is used as a bloc 
method. I understood the tests of Professor 
Roelofs with radial triangulation to be a strip 
method, and I think you get the best benefit if 
you use it as a bloc method. 
The automation process is pretty easy to 
apply in radial triangulation, and there are many 
ways to do it. One is the mechanical radial 
triangulation which mostly has been used for 
reconnaissance mapping, but when all the 
different weak points have been taken care of 
one can get very good results with a mechanical 
radial triangulation. One could also call it pre- 
cision radial triangulation. 
I am not trying to sell mechanical radial 
triangulation, but I think it should not only be 
regarded as that type of method which is used 
for reconnaissance mapping. It has been used 
to a very great extent and there are further 
possibilities for it. 
Prof W. SCHERMERHORN: I believe that Mr 
Fagerholm can be quite satisfied that there is 
hardly any method which has been used as 
much as his famous mechanical radial trian- 
gulation. 
Prof R. RoELOFSs: I completely agree with Dr 
Fagerholm that it is much better to treat radial 
triangulation as a bloc, and when I used strips 
in my geodetic examples it was because I was 
too lazy to study the propagation of errors 
through a bloc; with a strip it is much easier. 
Nevertheless, we had a practical example of a 
bloc of five strips of seven photographs, that 
means 30 sections, each section being two 
photographs. We adjusted this bloc by the Jerie 
method known to you, and the result was a 
relative standard error of 18 uw on photo-scale. 
Prof W. SCHERMERHORN: This last figure 
may give you the impression that nobody needs 
to be afraid on the precision of numerical radial 
triangulation. So far, there are only very few 
spatial triangulations which have obtained the 
precision in planimetry after bloc adjustment as 
this one which has been carried out. 
I have now finished the discussion on this 
subject. May I invite Dr Brandenberger, who is 
in charge of the second subject — Use of Auxil- 
iary Data for Carrying out Aerial Triangula- 
tions — to say a few words about this. I would 
call your attention to the fact that this paper 
has been published in Photogrammetria 1959/ 
1960 Congress-number A, on page 67.