Prismatic compass is a portable magnetic compass which can be either used as a hand instrument or can be fitted on a tripod. The type of blade useddepends on the nature of the task. The tripod is not required, the survey can be done by the instrument held in hand also. The horizontal angle is measured using a pair of sights located on the north-south axis of the compass. An astrocompass is a navigational tool that uses the positions of various astronomical bodies to determine the direction of true north. This compass is fine for plotting purposes. Magnetic bearing : A clockwise horizontal angle made by a line w.r.t magnetic meridian.
– Additional survival tricks, Indian mariners had first use of magnetic navigational compasses.
Eye Vane – Placed opposite to guide vane with an eye hole. Surveying done by a magnetic bearing compass instrument using a traverse method of calculation is known as compass surveying. Many hikers and drivers like this compass due to its relative reliability. July 23, 2017 shanmukha 2 Comments. Types of Compass in Surveying. If the bearing of the line AB is measured from B towards A, it is known as backward bearing or back bearing. Here angular measurements are taken using a compass and linear measurements are determined using chain or tape. GPS compass: GPS compasses are rapidly replacing the use of other traditional compasses. Magnetic compass is used to find out the magnetic bearing of survey lines. It usually a magnifying lens for map reading, some sort of light for low light conditions, and also a ruler. TYPES AND USES OF COMPASS.
5. Errors can be arising due to various reasons during the process of surveying, they are classified as: As the name suggests they are arise due to the wrong adjustments of the instruments.
July 23, 2017 shanmukha 2 Comments. It is measured by the magnetic bearing of the compass instrument. It is not recommended for the areas that are avoiding public attention and have the presence of iron ore deposits, magnetic substances like metallic or steel structures, electric cables conveying current, etc.
The survey involves evaluating land for making maps or plans for construction projects. Procedure, Methods, What is Tacheometer? The hacksaw comes in various designs, de-pending on the purpose.
Change ), You are commenting using your Google account. Selecting and using magnetic compasses. Compass surveying is an important branch of surveying which is usually adopted in determining the position of an object both by angular and linear measurements. •Compass surveying is not recommended for areas where local attraction is suspected due to the presence of magnetic substances like steel structures, iron ore deposits, electric cables , … The use of astro compass in determining the exact direction of true north requires the accurate information of time, date, longitudinal and latitudinal location.
Temporary adjustments are same as described in prismatic compass. Bearing in surveying.
Compass survey is generally use in large area. These bearing are observed by surveyors compass. In this system, the bearing of a line is measure eastward or westward from north or south, whichever is nearer. The compass is generally used to run a traverse line. ( Log Out / If it’s not, using the tripods, it should be held centrally over the peg. The magnetic needle swings freely over the horizontal circle which is divided into 360 degrees. The compass should be kept precisely over the station where the bearing is to be measured. They are: Natural errors are occurring due to the various natural causes which affect the working of compass. The magnetic bearings of a line can be determined by a magnetic compass. Modern surveying instruments provides faster and more precise surveying than conventional instruments. The graduations are divided into 4 quadrants. However, sometimes, the magnetic needle may be attracted and prevented from indicating the true magnetic meridian when there is certain magnetic substances. Magnetic North refers to the pole of Earth’s magnetic field.
They are usually mounted over a tripod and leveled using a ball and socket mechanism. Plane Table Survey- Principles, Advantages and disadvantages, Equipment, Accessories and their uses. The first will give the angle between two while the second will give the bearing of the line. And this thumb compass delivers on both counts. A magnetic meridian at a place is established by a magnetic needle which is uninfluenced by other attracting forces. Surveyor’s compass consists of a circular brass box containing a magnetic needle which swings freely over a brass circle which is divided into 360 degrees. This type of survey involves both record and field research, including any measurements and computations needed to set the boundary lines in accordance with applicable state laws. It is less precise compared to other advanced methods of surveying. Imperfect sighting of the ranging rods and inaccurate leveling also causes error. Magnetic Compass. It is measured by the magnetic bearing of the compass instrument. Change ), You are commenting using your Facebook account. Tacheometry survey is a branch of surveying in which horizontal and vertical distance are calculated with the help of measured horizontal distance and observed vertical angle. Bearing: A clockwise angle measured from a fixed datum(i.e meridian) is called bearing of line. (with diagrams) | types, TYPES OF ARCHES SHAPE FOR DESIGN | CONSTRUCTION METHOD, TYPES OF SHORING | RAKING, HORIZONTAL AND VERTICAL, TYPES OF SCAFFOLDING IN CONSTRUCTION | COMPONENT, CASE STUDY OF GURUNG HOUSES(SIKLES VILLAGE), WHAT IS CONTOUR LINE? This type of compass is commonly used in orienteering, a sport in which map reading and terrain association are paramount. According to this information, it is sighted on to any astronomical object with a known position to give an extremely accurate reading. Compass Surveying – Principles use of Prismatic Compass, Measurement of bearings, Conversion of bearings, Local attraction, Correction of compass traverse. Thumb compass is a type of base plate compass but smaller. It can be classified as, Satheesh is a Civil Engineer who has more than 9+ Years of experience in residential construction. You can follow and Like us on following social \rmedia.Website - http://ekeeda.comParent Channel - https://www.youtube.com/c/ekeedaFacebook - https://www.facebook.com/ekeedaTwitter - https://twitter.com/Ekeeda_VideoLinkedIn- https://www.linkedin.com/company-beta/13222723/Instgram - https://www.instagram.com/ekeeda_/Pinterest - https://in.pinterest.com/ekeedavideoYou can reach us at care@ekeeda.comHappy Learning : ) It is a type of compass in which a magnetized needle or dial and the compass card rest on a pivot inside a capsule that is completely filled with liquid. 5. For each survey line in the traverse, surveyors take two bearings that are fore bearing and back bearing which should exactly vary by 180° if the local attraction is somehow negligible.
Meridians: A fixed reference line w.r.t which a bearing of a line is taken is called meridian.
Enter your email address to follow this blog and receive notifications of new posts by email. It is a type of survey in which traverse length is measure by a tape and its bearing is measure by a magnetic compass. The bearings may either measured in Whole Circle Bearing (W.C.B) system or in Quadrantal Bearing (Q.B) system based on the type of compass used. On-chain surveying, we follow triangulation methods. The main two types of magnetic compass employed are a prismatic compass and a surveyor compass. Disadvantage of chain surveying is that, in it only distances are measured and hence area is to be covered with a network of triangles. Methods of plane table survey.