surveying

• Surveying


  The art and science of determining angular and linear measurements to establish the form, extent, and relative position of points, lines, and areas on or near the surface of the earth or on other extraterrestrial bodies through applied mathematics and the use of specialized equipment and techniques

  
• Classification of Surveying


  • Plane surveying
  • Geodetic Surveying

  
• Plane surveying


  • Considers the mean surface of the earth as plane
  • Plumb bob lines passing through the points are parallel to each other
  • The lines formed by joining two points on earth are considered as straight lines
  • The triangles formed are plane triangles
  • Solved using the knowledge of plane trigonometry
  • Uses normal survey and measuring instruments like chain, theodolite, measuring tape etc.

  
• Geodetic Surveying


  • Considers the mean surface of the earth as spherical
  • Plumb bob lines passing through the points intercept at the center of the earth
  • The lines formed by joining two points on earth surface are curved lines or arc lines
  • The triangles formed are spherical triangles
  • Solved using the knowledge of spherical trigonometry
  • Makes use of more sophisticated and precise instruments and modern technology

  
• Operations in Surveying


  • Control Survey
  • Boundary Survey
  • Topographic Survey
  • Hydrographic Survey
  • Mining Survey
  • Construction Survey
  • Route Survey
  • Photogrammetric Survey

  
• Measurement


  The process of determining the extent, size or dimensions of a particular quantity in comparison to a given standard
• Types of Measurement


  • Direct measurements
  • Indirect measurements
• In surveying, measurements are usually concentrated on angles, elevations, times, lines, areas, and volumes

  
• Linear Measurement Prefixes


  • mega - 1,000,000
  • kilo - 1,000
  • hecto - 100
  • deca - 10
  • deci - 0.1
  • centi - 0.01
  • milli - 0.001
  • micro - 0.000,001
  • nano - 0.000,000,001
• Linear Measurements


  Common units: kilometer, meter, centimeter, millimeter
• Area Measurements


  Common units: square meter, square kilometer, hectare
• Volume Measurements


  Common units: cubic meter, liter, milliliter
• Angular Measurement


  SI unit is the radian, defined as an angle subtended by an arc of a circle having length equal to the radius of the circle (2π rad = 360 deg)
• Units of Angular Measurement


  • Sexagesimal System (degrees, minutes, seconds)
  • Radian
• Sexagesimal System


  Divides the circle into 360 degrees, degrees into 60 minutes, and minutes into 60 seconds
• 1 circle = 360° = 21,600' = 1,296,000"
• 1° = 60' = 3600"
• 1' = 60"
• Radian


  The angle between radius lines from either end of an arc of radius length. 1 circle = 2π radians, 1 rad = 360°/2π = 57.29578°
• Measurement of Horizontal Distances


  • Distance by Pacing
  • Distance by Taping
  • Distance by Tachymetry
  • Distance by Graphical and Mathematical Methods
  • Distance by Mechanical Devices
• Distance by Pacing


  Counting the number of steps or paces in a required distance, where a pace is the length of a step in walking and a stride is equivalent to two paces
• Distance by Taping


  Stretching a calibrated tape between two points and reading the distance indicated on the tape
• Distance by Tachymetry


  An indirect method using a transit or theodolite to determine subtended intervals and angles on a graduated rod or scale, from which distances are computed by trigonometry

  
• Stadia Method


  A rapid means of determining horizontal distances using a telescope with horizontal hairs (stadia hairs) and a graduated rod (stadia rod)
• Distance by Graphical and Mathematical Methods


  Determining unknown distances through their relationship with known distances geometrically, used in plane table surveys and triangulation work

  
• Mechanical Devices for Distance Measurement


  • Odometer
  • Measuring Wheel
  • Optical Rangefinder
• Odometer


  A simple device that can be attached to a wheel for roughly measuring surface distance, similar to a vehicle's distance recorder
• Measuring Wheel


  A portable and self-contained measuring device with a small wheel attached to a rod and handle, which automatically gives distance readout as it is rolled along a line to be measured
• Optical Rangefinder


  A hand-held or tripod-mounted device that can determine distances approximately by focusing, operating on the same principle as a rangefinder on a single-lens reflex camera
• Odometer


  A simple device that can be attached to a wheel for purposes of roughly measuring surface distance. It is similar in function to the distance recorder of a vehicle speedometer.
• Measuring Wheel


  Very similar in operation to an odometer except that it is more portable and self-contained measuring device. It is basically consists of a small wheel which is attached to a rod and handle, and can be pushed by an operator. As the wheel of the device is rolled along a line to be measured, a built-in calibrated recorder automatically gives distance readout in meters and decimals of a meter.
• Optical Rangefinder


  It operates on the same principle as a rangefinder on a single-lens reflex camera. This device, which is usually hand-held or mounted on a small tripod, can be used to determine distances approximately simply by focusing.
• Photogrammetry


  The measurement of images on a photograph. The type of photographs used are those taken from an aircraft with the axis of the camera pointed vertically towards the terrain photographed.

  
• Leveling


  The process of directly or indirectly measuring vertical distances to determine the elevation of points or their differences in elevation.
• Uses of leveling results


  • Design highways, railroads, canals, sewers, water supply systems
  • Layout construction projects according to planned elevations
  • Calculate volumes of earth or other materials
  • Investigate drainage characteristics of an area
  • Develop maps showing general ground configurations
  • Study earth subsidence and crustal motion

  
• Level surface


  A curved surface which is at any point perpendicular to the direction of gravity or the plumb line. Surface of still water.
• Level line


  A curved line in a level surface, all points of which are normal to the direction of gravity and equidistant from the center of the earth.

  
• Horizontal surface


  A plane that is tangent to a level surface at a particular point.
• Horizontal line


  A straight line in a horizontal plane which is tangent to a level line at one point.
• Vertical line


  At any point is a line parallel to the direction of gravity.