Introduction to Surveying

Introduction to Surveying

• Surveying is 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 earth's surface.

Two General Classifications of Surveying

• Plane surveying: Assumes the Earth is flat, used for limited distances and areas.
• Geodetic surveying: Considers the Earth's spheroidal shape, used for large areas.

Types of Surveys

• Cadastral surveys: Determine property lines and boundaries in urban and rural areas.
• City surveys: Surveys of urban areas for planning, expansions, improvements, and map preparation.
• Construction surveys: Provide data for construction projects, including grades, reference lines, dimensions, and building locations.
• Forestry surveys: Data for forest management, including grades, and mensuration.
• Hydrographic surveys: Surveying bodies of water, including mapping shorelines, charting shapes of areas underwater, and measuring stream flow, important for navigation, water resource development, flood control, and recreation.
• Industrial surveys: Applying surveying techniques to industries to accurately measure and layout machines, shipbuilding, and aircraft assembly.
• Mine surveys: Determine underground mine excavations, surface structures, boundaries of mining claims, calculate excavated volumes, establishing lines and grades for mining projects.
• Photogrammetric surveys: Utilize photographs from aircraft or ground stations for mapping and measurements.
• Route surveys: Used for highways, railways, pipelines, canals, transmission lines for planning, design, and construction.
• Topographic surveys: Determine the shape of the ground and locations of natural and artificial features.

Development of Surveying Instruments

• Astrolabe: An early measuring instrument.
• Telescope: Used for astronomical observations.
• Transit: Used to measure and lay off angles, and establish lines of sight.
• Semicircumferentor: An early surveying instrument used for angle measurement.
• Plane table: A board attached to a tripod for leveling and measuring horizontal and vertical angles.
• Dioptra: An instrument for leveling and measuring angles, perfected by Heron.
• Roman Groma: An instrument used for aligning points.
• Libella: An instrument used to determine the horizontal plane.
• Vernier: An auxiliary scale for precise measurement of fractional parts of a main scale.
• Diopter: Another instrument for leveling and measuring angles.
• Compass: Used for determining directions and angles.
• Gunter's Chain: Early instrument for measuring distances.
• Chorobates: Instrument used for leveling work.
• Merchet: A device for time and meridian measurement.

Units of Measurements

• SI units for plane angles is the radian.
• Prefixes like kilo, mega, centi, milli, micro and nano are used to denote multiples or sub-multiples of units.

Significant Figures

• Rules for determining significant figures, including zeroes.

Types of Errors

• Systematic error: Errors consistently having the same sign and magnitude.
• Accidental error: Errors from external factors.
• Mistakes: Errors due to carelessness and poor judgment.
• Blunders: Large mistakes.

Sources of Errors in Surveying

• Instrument Errors: Errors arising (or introduced) from imperfections in instruments.
• Natural Errors: Errors from Natural phenomena like refraction, temperature, etc...
• Personal Errors: Errors caused by human limitations in observation, measurement, or execution.

Surveying Measurements

• Direct measurement: Comparison of measured quantity to a standard unit.
• Indirect measurement: Measuring a quantity by its relation to other known quantities.

Measurement of Horizontal Distances

• Pacing: Counting the number of steps (paces) for distance.
• Pace factor: Calculating the distance of one pace.
• Pedometer: A mechanical counter for paces.
• Passometer: A mechanical counter that counts paces strapped to the leg.

Measurement of Vertical Distances

• Direct or spirit leveling: Determining elevations of points by a series of leveling instrument setups.
• Reciprocal leveling: Establishing elevation differences between points that are far apart.
• Profile leveling: Obtaining elevations at specified intervals along a line.
• Trigonometric leveling: Calculating elevations using trigonometric relationships and measurements .
• Stadia leveling: Combining direct and trigonometric leveling for preliminary surveys or rough leveling.
• Barometric leveling: Determining elevations by measuring atmospheric pressure variations.
• Cross-section leveling: Creating short profile views (cross-sections) at regular intervals.
• Borrow-pit leveling: Determining relative elevations in excavation areas for calculating earthwork volumes.

Types of Levels

• Dumpy level: Widely used direct leveling instrument.
• Wye level: A leveling instrument with detachable telescopes.
• Builder's level: Used for building construction when precise measurement isn't required.
• Automatic level: Popular for conventional leveling work due to ease and speed of operation.

Measurement of Angles and Directions

• True meridian: Geographic north-south direction.
• Magnetic meridian: Direction given by freely suspended magnetic needle.
• Grid meridian: Reference direction aligned parallel with rectangular coordinates used in plane surveying.
• Assumed meridian: An arbitrarily selected reference line.

Units of Angular Measurement

• Degree: A unit in the sexagesimal system; a circle is divided into 360 degrees.
• Grad: A unit in the centesimal system; a circle is divided into 400 grads.
• Mil: A unit commonly used for military applications.
• Radian: One radian is equal to 180°/π, approximately 57.296 degrees.