Abstract
Recently, many industrial facories have beeu constructed along the beach on the new land reclamation areas in Japan. For the electric power supply to these big factories, electric air cables are set across the sea and rivers, often crossing shipping routes. Many accidents have occurred from ships contacting the cable as they pass under it, and nowadays many ocean freighters visit Japan from overseas. To measure the height or the vertical clearance of these cables, the authors used the method of terrestrial photogrammetry. When using the classical method of determining the height of cable over the water, it is difficult to identify of the same point on the wire from different observation points. The photogrammetric method, which is much less laborious, is a superior to the classical method in the following respects:
1. The field work can be done in a shorter time with the same required accuracy.
2. As the condition of the object at the time of photographing can be reproduced at any time later by using a plotting instrument, the result of plotting and measurement can be checked again later with ease.
3. The co-ordinates of the points on the cable are also recorded in type on a sheet of paper by the EK 3 automatic co-ordinate printer attached to the plotting instrument A7.
Photography was done on the 2nd of Nov. 1963 using two bases of length 24.272m and 19.205m.
The plates which were used were fine-grain orthoplate, S. G. 10 made by akura Co. Ltd. in Japan.
The control points used for the orientation were surveyed with the T. M. 10 Sokkisha theodolite. These control points were set along the beach. The results of measurement with the A 7 autograph were checked against the design catenary formula anb also compared with the control co-orbinates, which were measured in the field. From these data, it was found that photogrammetry can be used very effectively with a high accuracy in a limited time.
