should be supported by two further observa- 
tions: ; 
1. the low cost of orthophotography allows for 
frequent improvements 
2. orthophotography guarantees a close contact 
between photointerpretation used in various 
special fields and geographical localization. 
Mr. H. Belzner (F.R.G.) reported that Commission 
D of OEEPE was preparing a new project for the 
revision of maps made at the scale of 1:25000. 
One of the areas to be covered by this project 
was a comparison of the techniques of stereo- 
restitution with orthophotography. 
Mr. J. Kure (Netherlands) pointed out that a com- 
parison of the results obtained from orthophoto- 
interpretation and linemap interpretation is not 
fair as the quality of orthophotos is inferior to 
that of original photos. Consequently, the use of 
original photos should be sufficient, if interpre- 
tation is required when working with orthophotos. 
Dr. M. Zolfaghari (Iran) asked what the future of 
orthophotography would be in relation with clas- 
sical photogrammetry on the basis of the ex- 
periments presented by Dr. Ackermann. 
Dr. Ackermann answered by saying that a satis- 
factory result can be obtained only if the scale 
between the orthophotograph and the original 
photo does not exceed 2. 
Mr. O. Johansson (Sweden) participated in the 
discussion by reporting that an economic map 
of Sweden had been made on the basis of 
orthophotos at a scale of 1:10000 produced from 
original photos at a scale of 1:30000, and with 
very good results. Orthophotography had been 
combined with intensive complementary work 
carried out in the terrain. 
Author: Mr. G. Agarwal (India) 
Title: Accuracy of spot Heights and De- 
termination of Minimum Contour In- 
terval for Plotting PP IV/01 
Presented by Colonel M. Datta (In- 
dia) 
Thursday, July 15, 1976, from 9.00 to 10.30 
Session 3 of Commission IV 
Topic: Checking and Up-Dating Topo- 
graphic Maps 
Chairman: — Mr. G. Ducher (France) 
This session was dedicated to reports on the 
activities of WG IV/4 "Checking of Topographic 
Maps” and WG IV/2 ”Up-Dating of Topographic 
Maps”. 
Working Group Papers 
Author: Mr. D. Crémont (France) 
Title: Checking of Topographic Maps 
Mr. Crémont presented the main conclusions 
that had been reached in the course of the in- 
vestigation conducted by him. He regretted that 
the answers received had been insufficient. 
With regard to the inscription of classification 
codes on documents, indicating their accuracy 
and contents, it was suggested that an interna- 
tional committee be established to study the 
problem. 
108 
The other problems involved in the said investi- 
gations concerned the nature of checking and 
checkers and the costs of the operations required. 
The costs varied between 396 and 2096. 
Then Mr. Crémont mentioned the research work 
carried out by Mr. Pichlick (Czechoslovakia) and 
the experiments made with the Pe&ny polygon. 
He then reported on the experiments made at 
I.G.N. with the basic maps (1:25000 and 1:5000), 
describing the checking method used, and gave 
some of the results obtained. 
It was recommended that the same photography 
be used as that for the mapping itself (or a photo- 
graphy at the same scale and following the same 
flight plan). Nevertheless, Dr. B. Dubuisson (Fran- 
ce) pointed out that in this case the errors of the 
photography are not taken into account. The 
costs should vary between 8% and 10% of the 
total costs of the mapping process. 
Author: Dr. G. Birardi (Italy) 
Title: Revision of Topographic Maps WGR 
1V/03 
Dr. Birardi presented a report on the activities 
of his Working Group, which concentrates 
its efforts on the study of the up-dating of topo- 
graphic maps. He listed the conclusions reached 
on the basis of a study of the answers given to 
the questionnaire on up-dating and concerning 
all aspects of the problem. 
In the course of the general discussion that 
followed, Dr. K. Szangolies (G.D.R.) said it seemed 
that Dr. Birardi's appeal to the manufacturers of 
instruments specially designed for up-dating 
purposes had been heard. He added that this 
was true of Zeiss Jena, in particular, which 
brought forth the Topoflex. 
Then Mr. E. Huber (Switzerland) reminded the 
audience that only a part of the information 
required for the up-dating of maps could be 
obtained by photogrammetric means, and that a 
number of operations was required for the trans- 
formation of this information. 
To close up with, there was an exchange of ideas 
on the role of orthophotography in relation with 
linemaps and their up-dating. 
Thursday, July 15, 1976, from 10.45 to 12.15 
Session 4of Commission IV 
Topic: Revision 
Chairman:  Dr.G. Birardi (Italy) 
Panel Discussion 
Topic: Revision 
Moderator: Dr. G. Birardi (Italy) 
Panelists: Dr. F. Doyle (U.S.A) 
Mrs. E. Fleming (Canada) 
Mr. M. Thompson (U.S.A.) 
Mr. D. Glendinning (Australia) 
Mr. G. Ducher (France) 
Mr. L. van Zuylen (Netherlands) 
Dr. B. Dubuisson (France) 
Dr. S. Dequal (Italy) 
Mr. H. Yzerman (Switzerland) 
Mr. G. Hardy (U.K.) 
Mr. Ducher led off by describing the procedures 
for revision of basic topographic maps (1:25000)