P1254413674FszjC

1
CH. 3 LEVELING
4/15/03
2
Read Kavanagh Ch. 3

• 3.1 Know these definitions (not verbatum)
• 3.2-3.3 Understand the divergence between a
  horizontal line and a level line, and the
  proportionality of error due to curvature and
  refraction with distance of the shot.
• 3.4 Skim read, except read 3.4.2 Level Tube.
  Understand the relationship between the optical
  quality and precision of the level, and the
  radius of curvature of the level tube.
• 3.5 Skip.
• 3.6 Know what a compensator does, and
  conceptually how it works.
• 3.7-3.8 Skim read. Become generally familiar
  with what a digital level is, and what a bar
  code is, and how they work.
• 3.9-3.10 Skim read.
• 3.11 Know what these terms mean.
• 3.12 Understand differential leveling procedure
• 3.13 Skim read for Field Exercise. Know how to
  hold a rod, and rocking (waving) the rod.
  Know how to read the rocking rod. Understand
  field notes for leveling
• 3.14 Skim read.
• 3.15 Skim read. Understand Table A.11
• 3.16 Differentiate between plan, profile, and
  cross-section views. Understand Fig. 3.22.
  Understand profile and cross-section field note
  formats.
• 3.17-3.20 Skip.
• 3.21 Understand the concepts of allowable error
  and adjusting a level loop.
• 3.22-3.24 Read for Field Exercise.

3
3.1 Definitions

• Leveling a procedure used to determine
  elevations of points or differences in elevation
  between points
• Elevation vertical distance above or below a
  reference datum.
• Datums
• Mean sea level a universally employed reference
  datum.
• National Geodetic Vertical Datum (NGVD) of 1929.
• North American Vertical Datum (NAVD 88).
• MOST AREAS USE MEAN SEA LEVEL AS THEIR DATUM,
  either NGVD 29 or NAVD 88

4
VERTICAL DATUMS

• MEAN SEA LEVEL DATUM OF 1929
• NATIONAL GEODETIC VERTICAL DATUM OF 1929
• (As of July 2, 1973)
• NORTH AMERICAN VERTICAL DATUM OF 1988
• (As of June 24, 1993)

5
COMPARISON OF VERTICAL DATUM ELEMENTS

• 
  NGVD 29
  NAVD 88
• DATUM DEFINITION 26 TIDE GAUGES
  FATHERS POINT/RIMOUSKI
• 
  IN THE U.S. CANADA
  QUEBEC, CANADA
• BENCH MARKS 100,000
  450,000
• LEVELING (Km)
  102,724
  1,001,500
• GEOID FITTING Distorted to Fit
  MSL Gauges Best Continental
  Model

6
NGVD 29 and NAVD 88
7
4
8

• Benchmark (BM) a reference mark whose
  elevation is known relative to a given datum.
• Backsight a point which is to be used to
  determine the elevation and/or angular
  orientation of the surveying instrument
• Foresight a point to which an instrument
  sighting is made for measuring or establishing
  its elevation and/or its horizontal position
• Turning Point a temporary point whose
  elevation is determined during the process of
  leveling used to establish the Height of
  Instrument
• Height of Instrument in leveling, the height
  of the line of sight of the leveling instrument
  above the adopted datum in horizontal angle
  measurement, the height of the center of the
  telescope (horizontal axis) above the ground or
  station mark.

9
3.2 Differential Leveling Procedure
10
How to Read a Level Rod
11
How to HoldA Level Rod
12
Notes on How To Perform Differential Leveling

• Level the instrument by centering the bullseye
  level
• Focus two things 1) cross-hairs 2) object to
  avoid parallax error
• Rodperson starts at backsight (pt. of known
  elev.), rocks rod or uses level rod bubble
• Field notes (see example). Note that sums of BS
  and FS should equal.
• Rodperson choose turning points for
  reproducibility
• Avoid collimation error by making backsights and
  foresights the same length