TACHEOMETER SURVEYING WITH AN ORDINARY THEODOLITE. 



TACHEOMETER SURVEYING with an ORDINARY 



THEODOLITE. 



By Thomas Kennedy, Assoc m. inst. c.e. 



[Read before the Engineering Section of the Royal Society of N. S. Wales, 

 and the Institution of Surveyors N. S. Wales, July 20, 1904.] 



Tacheometer surveying consists in getting heights and 

 distances without chaining and levelling in the ordinary 

 manner. It is proposed to describe a simple system of 

 tacheometry that can be taken with an ordinary theodolite 

 and so avoid the use of special instruments or fixed stadia 

 wires in the theodolite. 



This system of tacheometry has recently been used on an 

 extremely rough railway trial survey on part of the North 

 Coast, being the ascent to the Dorrigo Tableland from the 

 Orara River. The country is mostly covered with a dense 

 undergrowth, the clearing of which added to the difficulty 

 of the survey, as every line had to be cleared for observa- 

 tions. It was found possible, however, by this method of 

 tacheometry to stake level and cross level from 60 to 80 

 chains in a day besides reducing all field notes. The ascent 

 from the valley of the river to the tableland was almost 

 abrupt, the total rise being 1,700 feet, and the direct dis- 

 tance from the river to the top being about six miles. A 

 distance of 18 miles had to be developed to get the ruling 

 grade. The first mile was level, so practically the whole 

 ascent had to be made on the ruling grade rising approxi- 

 mately 100 feet to the mile. The field work of the survey 

 was commenced on the 1st May and completed on the 1st 

 August (three months). The plans were plotted in Head 

 Office. 



The method is known as the " Tangential" and consists 

 in setting on the vertical arc of the theodolite consecutively 



1-Julv20, 1904. 



