din 
- à. 
- 
  
  
E 
4 
  
  
  
  
  
  
  
160 THE CANADIAN SURVEYOR May, 1960 
3. It seems that human factors are greatly responsible for appreciable errors of 
a systematic character, which may be positive or negative. They may impose the 
limit to the ultimate accuracy obtainable. More attention should be devoted to this 
question. 
4. Instrumental and photographic image stability seems to be satisfactory and 
may justify the use of empirically-determined global corrections in future mapping 
technique. 
5. The vertical accuracy actually obtainable is higher than the often-quoted values. 
6. The quality of plots varies very widely and this particular question requires 
special studies. 
7. Anaglyphic-type plotters that have the advantage of a low price are less 
accurate and they seem to be slower than the non-anaglyphic plotters. 
ACKNOWLEDGMENTS 
The author wishes to express his appreciation to the members of the Photo- 
grammetric Research Group of the National Research Council of Canada for their 
most valuable assistance in the organization of the project and in the compilation of 
results, in particular to Mr. A. Way-Nee for his excellent preparation of photographic 
material and to Mr. A. Richens for his most conscientious performance of instrumental 
experiments. 
Due acknowledgment is also expressed to the participants without whose complete 
cooperation this project would not have been possible. 
ANALYSIS OF CONTOUR ERRORS 
by G. C. TEWINKEL 
Photogrammetry Division, U.S. Coast and Geodetic Survey 
Member of Commission IV-3 
The topographic specimens from the Second International Mapping Experiment 
were tested for faithfulness in contouring at the following three separate small areas: 
Area No. 1. A very flat area, average slope about tan a — 0.003, a distance of 
about one kilometer. 
Area No. 2. A broken hilly area, average slope tan o = 0.158, a distance of about 
one kilometer. 
Area No. 3. A profile over various types of terrain, very steep, very flat, wooded 
and cultivated, a distance of 1.7 kilometers. 
As a basis for the contouring tests, the test sections were very carefully surveyed 
with the latest self-reducing tacheometers in fine adjustment. The surveys were 
executed by personnel of the National Research Council under the direction of this 
writer, who worked with them for one week in the selecting and measurement. The 
data were reduced by the National Research Council of Canada, with closures and dis- 
crepancies far too small to have any significance on the photogrammetric appraisal. 
In each phase of the survey, no effort was spared to remove every doubt concerning the 
validity of the field observations. Only part of the hilly area remained to be surveyed 
after the writer’s departure: this area was well begun the first week but required more 
time for completion the following week. 
After completion of the office work, the results of the surveys, together with the 
cest specimens, were sent to the writer and were measured and computed by him and his 
colleagues in the Photogrammetry Division of the U.S. Coast and Geodetic Survey in