Least count of theodolite

Contents • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • Theodolite Survey • A theodolite is an important instrument used for measuring horizontal and vertical angles in surveying. • The system of surveying in which the angles (both horizontal & vertical) are measured with the help of a theodolite, is called Theodolite surveying. Applications of Theodolite Survey • Measuring horizontal and vertical angles. • Locating points on a line. • Prolonging survey lines. • Finding difference of level. • Setting out grades • Ranging curves • Tacheometric Survey • Measurement of Bearings Compass Surveying Vs Theodolite Surveying • Horizontal angles are measured by using a Compass with respect to meridian, which is less accurate and also it is not possible to measure vertical angles with a Compass. • So when the objects are at a considerable distance or situated at a considerable elevation or depression, it becomes necessary to measure horizontal and vertical angles more precisely. So these measurements are taken by an instrument known as a theodolite. Classification of Theodolite Theodolites may be classified as: • Transit Theodolite. • Non Transit Theodolite. Transit Theodolite A theodolite is called a transit theodolite when its telescope can be rotated through 180° in a vertical plane about its horizontal axis, thus directing the telescope in exactly opposite direction. Non Transit Theodolite A theodolite is called a non transit theodolite when its telescope can...

After reading this article you will learn about the direct vernier and retrograde vernier . 1. Direct Vernier: Principle: If it is required to read 1/nth part of the smallest division on the main scale, (n-1) main divisions are taken and divided into n equal divisions on the vernier scale as shown in Fig. 9.2. Here 9 divisions on the main scale have been divided into 10 divisions on the vernier scale. In this case, the vernier scale divisions are shorter than the main scale divisions. Let d= the value of the smallest division on the main scale. ADVERTISEMENTS: v = the value of the smallest division on the vernier scale. n = the number of divisions on the vernier. Then, nv=(n-1)d The difference between the value of a division on the main scale and that on the vernier scale =d-v. This difference is known as the least count of the vernier. The least count of the vernier shown in fig. 9.2. is equal to 1/10th of the smallest division on main scale. ADVERTISEMENTS: The value of the least count of a vernier may, therefore, be obtained by dividing the value of the smallest division on the main scale by the number of vernier divisions. In this type of vernier, both scales are graduated in the same direction, i.e. both, either from right to left or from left to right. Reading a Vernier: (i) Determine the least count of the vernier. ADVERTISEMENTS: (ii) Note the main scale graduation beyond which the index lies. This is the approximate reading. (iii) Observe which division of the ver...

Contents • • • • • • • • • • • • • • • • • • • • • • Objective: The main objective of this job is to set out a simple circular horizontally using Rankine’s method. Apparatus: • Theodolite • Ranging pole • Ranging rod • 10 pegs • Fiber glass tape • Mallet Least count of instruments: Least count of theodolite = 00°00’05’’ Least count of fiber glass tape = 0.01 m Related Theory Simple circular curve A simple circular curve is defined as a Horizontal curve comprised of a single arc with a constant radius connecting the two tangents. It is the most commonly used horizontal curve. Its practical example is a simple arc provided in the road or railway track to impose a curve between two straight lines. Point of curvature The location of the curve’s starting point is allocated as the point of curvature represented by “P 1“. Point of tangency The location of the endpoint of the curve is allocated as the point of tangency represented by “T 2”. Point of intersection of the tangents The point of intersection of the tangents is the point where the two tangents intersect and this point is also called the vertex. Length of a tangent The length of a tangent starts from “T 1” to “I” or from “I” to “T 2”. Apex of a curve Apex is the distance from “I” to the midpoint of the curve. Versed sine of the curve Versed sine of the curve is the distance from the midpoint of the curve to the midpoint of the chord. Length of a chord The length of the chord is the displacement from “T 1” to “T 2“. Lengt...

Table of Contents • • • • • • • • • • • • • • • • • • • • • • • • • • The total station in surveying is an instrument that is primarily designed as a combination of electronic transit theodolite, an electronic distance meter (EDM), and software that runs on a computer which is referred to as the data collector. The surveyor can use the total station for various purposes such as determining the angles, measurement of distances, etc. Total Station is widely used in modern surveying, archaeology, mining, private accident reconstructions, etc. ✔ By the use of triangulations and trigonometric calculations; the measured angles and the distances can be used to determine the actual position of the required points or even the position of the total station from the known points in absolute terms. ✔ Most of the total stations these days consist of a The interface design is done such that the advantages of both the technologies are ensured (i.e. In GPS; the line of sight is not required between the consecutive measurement points. While in the traditional total station; high precision measurement is required especially in the vertical axis in comparison to the GPS). ✔ The total station is the survey instrument that measures the angles by making use of the electro-optical scanning of the extremely precise digital bar-codes that are attached to rotating glass cylinders or discs present within the instrument. The high-quality total station is even capable of measuring the angles down to 0...

Table of Contents • • • • • • • What is the accuracy of a theodolite? A number of investigators reported results of similar tests using theodolites, not levels. For distances less than 150 m, almost all investigators reported accuracy values in the range from 1/600 to 1/2100. What is the accuracy of 1 second in total station? Product Specification Brand Sokkia Angle Measurement Accuracy 1 Second Model Number IM-101 Data Storage Pen Drive 2 to 32 GB Magnification 30X/2.4″ How do you test theodolite accuracy? • Having set up the theodolite and checked the Plate Bubble as described previously, level the tribrach with theodolite or plate level over a point defined by a cross (the finer the cross the better). • Level and centre over a point defined by a cross. • Rotate the theodolite through 120 degrees and observe the cross. What is the smallest accurate reading that can be measured in a theodolite? The accuracy in modern first-order or geodetic instruments, with five-inch glass circles, is approximately one second of arc, or 1/3,600 of a degree. With such an instrument a sideways movement of the target of one centimetre can be detected at a distance of two kilometres. What is optical theodolite? A theodolite /θiːˈɒdəlaɪt/ is a precision optical instrument for measuring angles between designated visible points in the horizontal and vertical planes. What are theodolites used for? theodolite, basic surveying instrument of unknown origin but going back to the 16th-century English...