Methods of Determining Distance by Pacing

Methods of Determining Distance

• Distance by pacing is suitable for approximate distances in small-scale mapping, locating details, and reconnaissance surveys.
• Pace Factor is the average number of paces per meter and is affected by speed, ground roughness, clothing, shoes, fatigue, and terrain slope.
• Unknown distance can be calculated by multiplying the average number of paces by the pace factor.

Distance by Taping

• Taping is a direct method of measuring horizontal distances using a calibrated tape.
• The taping party consists of a Head Tape man, Adjustment of Level Tube, and others.
• Composition of taping party includes:
  • Head Tape man: responsible for accuracy and speed of linear measurements.
  • Adjustment of Level Tube: makes the axis of the level tube parallel to the axis of wye.
  • Adjustment of Horizontal Cross-Hair: makes the horizontal cross-hair lie in a plane perpendicular to the vertical axis.

Builder Level

• Used in building construction where high precision is not required.
• Level vial is not as sensitive as in other levels, and its telescope has less magnifying power.
• Used for setting concrete forms, batter boards, and establishing grades for earthwork.

Automatic Level

• Similar to the dumpy level, but with a compensator that helps the instrument to level automatically.
• Compensator is also called a stabilizer and consists of two fixed prisms that create an optical path between the eye piece and objective.

Tilting Level

• Allows for horizontal rotation and rotation about 4 degrees in its vertical plane.
• Main advantage is that it is useful when few observations are to be taken with one setup of the level.
• Can be tilted or rotated about its horizontal axis.

Roles in Taping

• Recorder: keeps a record of measurements, sketches, and observations.
• Flagman: holds the range pole (or flagpole) at selected points.
• Rear Tape man: assists the Head Tape man during a taping operation.

Procedure of Taping

• Aligning the tape
• Stretching the tape
• Plumbing
• Marking full tape lengths
• Tallying taped measurements
• Measuring fractional lengths

Corrections in Taping

• Too long = add
• Too long laid out = subtract
• Too short = opposite of the first two rules
• Corrections are required for:
  • Tape not of standard or nominal length
  • Ends of the tape not held at the same level
  • Inaccuracy in keeping the tape along a straight line
  • Tape not of nominal length due to temperature differences
  • Shortening or lengthening of the tape due to pull on its ends
  • Distance between end points of an unsupported length of tape is less than the specified nominal length

Definitions of Terms

• Benchmark (BM): a fixed point of reference with a known or assumed elevation.
• Backsight (BS): a reading taken on a rod held on a point of known or assumed elevation.
• Foresight (FS): a reading taken on a rod held on a point whose elevation is to be determined.
• Backsight Distance (BSD): measured from the center of the instrument to the rod on which a backsight is taken.
• Foresight Distance (FSD): the horizontal distance from the center of the instrument to the rod on which a foresight is taken.
• Turning Point (TP): an intervening point between two benchmarks on which point foresight and backsight rod readings are taken.

Leveling

• Leveling is the process of directly or indirectly measuring vertical distances to determine the elevation of points or their differences in elevation.
• Level surface: a curved surface that at every point is perpendicular to the local plumb line.
• 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.
• Mean Sea Level: a reference point for measuring elevations.