23878 Determine differences in height for survey practice



|Title |Determine differences in height for survey practice |

|Level |4 |Credits |7 |

|Purpose |This unit standard is for people who are working, or who intend to work, in the surveying profession as|

| |a survey technician. |

| | |

| |People credited with this unit standard are able to: describe the accuracy capabilities and ranges of |

| |surveying instruments for measuring differences in height; explain methods for measuring differences in|

| |height using conventional surveying instruments; explain errors and reductions in measuring differences|

| |in height; prepare to determine vertical heights for surveying using conventional surveying |

| |instruments; record and reduce field observations for differences in height; and determine height |

| |differences and reduce levels for different topography. |

|Classification |Surveying > Survey Practice |

|Available grade |Achieved |

Guidance Information

1 The following legislation and documentation must be complied with:

Cadastral Survey Act 2002;

Price, WF, and Uren, J, Surveying for Engineers (UK: Palgrave Macmillan, 2005), available at ;

Standards specified by Land Information New Zealand are available on the geodetic information pages at ;

instrument specifications;

job specifications;

manufacturers’ instructions.

2 Definitions

GPS refers to the United States NAVSTAR GPS or Navigation Signal Timing and Ranging Global Positioning System.

Conventional surveying instruments refer to surveying instruments such as tape, steel bands, levels, sextants, theodolites and total stations, and exclude data receivers for global navigational satellite systems.

Workplace procedures refer to documented procedures specific to an enterprise which set out the quality management requirements for the business practice and activities of that enterprise.

Outcomes and performance criteria

Outcome 1

Describe the accuracy capabilities and ranges of surveying instruments for measuring differences in height.

Range instruments – theodolite, total station, optical level, laser level, digital level, sextant, abney level;

evidence is required of at least three items of equipment.

Performance criteria

1.1 The accuracy and range of surveying instruments for measuring differences in height are explained in accordance with instrument specifications.

1.2 The appropriateness of surveying instruments for measuring differences in height is explained in terms of achieving specified accuracy.

Range accuracy – third Order spirit levelling with a maximum closure error of ±7 mm sqrt(k), where k is the distance in kilometres.

Outcome 2

Explain methods for measuring differences in height using conventional surveying instruments.

Performance criteria

2.1 Trigonometric methods for measuring differences in height are explained in relation to the instruments used and, where relevant, in accordance with instrument manufacturer’s instructions.

Range methods – double face readings, reciprocal vertical angles, multiple sets;

instruments – theodolite, total station, optical level, laser level, digital level, sextant.

2.2 Methods of differential levelling are explained in relation to the instruments used and where relevant in accordance with instrument manufacturer’s instructions.

Range methods – open run, closed loop, equalising backsight and foresight distances.

2.3 Methods for measuring differences in height using GPS are explained in accordance with instrument manufacturer’s instructions.

Outcome 3

Explain errors and reductions in measuring differences in height.

Performance criteria

3.1 Angular measurement for differences in height is explained in terms potential errors.

Range error types – systematic, gross, random;

potential errors include but are not limited to – bisecting the mark, earth curvature, refraction, grazing rays.

3.2 Differential measurement is explained in terms potential errors.

Range error types – systematic, gross, random;

potential errors include but are not limited to – collimation, misidentification, misreading, recording, instrument, parallax, estimating the reading, staff, grazing rays.

3.3 The importance of using independent checks to find and remove errors in angular and differential measurement is explained, and methods for finding them are demonstrated in accordance with instrument manufacturer’s instructions.

Range three errors.

3.4 Reductions on differences in height are explained in terms of adapting raw measurements to refined data.

Range reductions relating to – sea level, close, mean.

Outcome 4

Prepare to determine vertical heights for surveying using conventional surveying instruments.

Performance criteria

4.1 Conventional surveying instruments are selected for determining vertical heights to achieve the degree of accuracy in accordance with job specifications.

Range a job specifying third (or numerically lower) Order spirit levelling with a maximum closure error of ±7 mm sqrt(k), where k is the distance in kilometres;

instruments include but are not limited to – optical or digital level, theodolite, total station, laser level.

4.2 A method for determining vertical height is selected in accordance with job specifications.

Range may include but is not limited to – differential levelling, vertical angles.

4.3 The selected surveying instruments are checked for calibration requirements in accordance with instrument manufacturer’s instructions.

Range two peg test, vertical circle index;

may include supplier or service centre documentation.

Outcome 5

Record and reduce field observations for differences in height.

Performance criteria

5.1 Differential measurements and field data are recorded in accordance with job specifications.

Range field book, or data recorder.

5.2 Recorded measurements for trigonometrical levelling are verified and reduced in accordance with workplace procedures.

Range verification – summing of vertical angles, mean of left face and right face observations, mean of all observations;

reductions – calculate ∆H.

5.3 Recorded measurements for differential levelling are verified and reduced in accordance with workplace procedures.

Range verification – backsights minus foresights = rises minus falls = last reduced level minus first reduced level, or ΣIS + ΣFS + ΣRLs except first = Σ (each HPC x number of applications);

reductions – rise and fall, height of plane of collimation.

5.4 Reduced trigonometric and differential measurements are verified as correct in relation to a known height difference in accordance with a precision standard of third (or numerically lower) Vertical Order of Height as defined by Land Information New Zealand.

Outcome 6

Determine height differences and reduce levels for different topography.

Range topography – flat, undulating, steep.

Performance criteria

6.1 Field observations for vertical height are sighted and recorded in accordance with job specifications.

Range < 100 m, < 500 m.

6.2 All determinations are checked in accordance with workplace procedures.

6.3 Closing errors are calculated and distributed in accordance with job specifications.

|Replacement information |This unit standard replaced unit standard 8777. |

This unit standard is expiring. Assessment against the standard must take place by the last date for assessment set out below.

Status information and last date for assessment for superseded versions

|Process |Version |Date |Last Date for Assessment |

|Registration |1 |25 February 2008 |31 December 2021 |

|Review |2 |28 November 2019 |31 December 2021 |

|Consent and Moderation Requirements (CMR) reference |0101 |

This CMR can be accessed at .

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