Geodetic Surveying

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Lecture 4

• Geodetic Surveying

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Role and Aims

• 3D coords for surveying and mapping on a
  national, regional or continental basis.
• provides the control framework for less precise
  surveys for topographic, cadastral and
  engineering, mapping and LIS, GIS systems
• determination of the size and shape of the earth
• research and development
• crustal and tectonic motion studies

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History of Australian Geodetic Surveys
Use notes from last year for vertical and
horizontal history
4
Class and Order of Geodetic Surveys
Include Back ground from Selbys notes and
definitions of order from last years notes
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Class and Order of Geodetic Surveys
The surveying and mapping of Australia at the
national level is a co-operative enterprise
shared between a number of Commonwealth and State
agencies. Such an enterprise demands a high
degree of co-operation between the
participating agencies and in the past this has
been facilitated by coordination through the
National Mapping Council (NMC). The NMC was
replaced in 1988 by the Inter-Governmental
Committee on Surveying and Mapping (ICSM) which
has, as one of its functions, the requirement to
maintain and develop technical standards and
specifications. This document defines the
standards and specifications relevant to control
surveys. Fundamental geodetic networks of
horizontal and vertical control provide Australia
with a national asset in the form of
fixed homogeneous coordinate reference systems.
These systems are inherent to the national
technological infrastructure as they form the
basis of all spatially related information.
Control surveys which are tied to the coordinate
reference system are to be assigned a CLASS
commensurate with their designed and achieved
precision and an ORDER commensurate with
the assigned CLASS and their fit to the fixed
coordinate reference system. CLASS and ORDER are
to be assigned by the Authority undertaking the
survey or by appropriate Commonwealth or State
Authorities where surveys are specifically
designed to provide densification of the
fundamental geodetic network. A guide to the
application of CLASS and ORDER is given in Part
A, Annex B. Control surveys which are tied to the
coordinate reference system are to be adjusted
using approved computer programs. A National
Geodetic Data Base (NGDB) is held and maintained
on behalf of ICSM by the Australian Surveying and
Land Information Group (AUSLIG). Recognising that
technological developments may well lead to an
increase in the contribution by non-ICSM members
to the densification of the fundamental geodetic
networks, it is considered desirable that
Government authorities responsible for the
geodetic survey in their State or Territory
endeavour to acquire information on surveys
carried out by non-ICSM members which may assist
in the densification of the geodetic network
Information acquired be assessed by the
appropriate authority to determine its
suitability for inclusion in the NGDB
Information in the NGDB be available to all users
concerned with the planning and conduct of
surveying or mapping projects or with the
development of spatially based information
systems. Although SP1 this publication was not
designed to cover specific issues of cadastral
surveys, some Authorities or States may choose to
refer to it for that purpose.
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Class and Order of Geodetic Surveys

• Specification Design the level of accuracy and
  precision which need to be achieved to meet a
  prescribed class or order of survey
• ICSM document available on the web
  http//www.anzlic.org.au/icsm/sp1/sp1.htm
• CLASS is a function of the planned and achieved
  precision of a survey network and is dependent on
  the following
• the network design
• the survey practices adopted
• the equipment and instruments used
• the reduction techniques employed
• ORDER is a function of the class of the survey,
  the conformity of the new survey data with an
  existing network coordinate set and the precision
  of any transformation process required to convert
  results from one datum to the next - accuracy.

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Class of Survey

• planned precision
• minimally constrained least squares solution
• stats related purely to the new survey
• achieved precision can never exceed planned
  precision - lower class can be assigned
• Adherence to the recommended practices described
  in Part B is not mandatory in order to achieve a
  given CLASS. However, if not used the onus is on
  the user to prove that the practices used will
  achieve the desired level of precision

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Order of Survey

• order assigned cannot be higher than the order of
  the existing stations constraining the network
• order cannot be higher than the class assigned to
  that survey
• numerically increasing order implies decreasing
  accuracy

.
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Relationship between Class and Order
Highest order which may be assigned to a station
from a survey of given class is shown
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Relationship between Class and Order

• class is an attribute of the survey observation
  and order is an attribute of a specific
  coordinate value

An observation carried out to establish a new
point could be to Class A precision, its GDA94
coordinates could be classified as 1st Order,
but its AGD84 coordinates may be to 3rd Order
standards. ie the AGD84 network constraining the
the new point may have had significant
distortions which have been resolved in the
GDA94 readjustment.
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Determining Class and Order

• The allocation of Class to a survey on the basis
  of the results of a successful minimally
  constrained lest squares adjustment may generally
  achieved by assessing whether the semi-major axis
  of each relative error ellipse is less than or
  equal to the length of the maximum allowable
  semi-major axis r using the following formula

r c ( d 0.2 )
r maximum allowable semi-major axis in mm c
empirically derived factor represented by
historically accepted precision for a
particular standard of survey d distance to any
station in km
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Example of the application of Class and Order
Use ICSM example and include vertical class and
order comparisons
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Terrestrial Geodetic Measurements

• Geodetic measurements require separate
  consideration to typical survey measurements
• the longer ranges of geodetic measurements
  (10-150km) require more attention to field
  procedures, precision and accuracy
• 4 essential types of conventional terrestrial
  measurements level differences, horizontal
  angles, vertical angles and distances

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Recommended Survey and Reduction Practices
Page from ICSM
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Level Differences
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Horizontal Angles
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Distances
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Vertical Angles