1Surveying technique to determine relative
positions of widely spaced points, lengths, and directions which
require the consideration of the size and shape of the earth. (Takes
the earth’s curvature into account.)
used to provide control points to which small
surveys can be connected.
Geodetic Surveying
2 Use to established a horizontal control system for a country
process of a measuring
system comprised of connected triangles
Triangulation
3Precisely measured line in triangulation is called
base line
4Vertices of the individual triangles are known
triangulation stations
5measured at suitable intervals to minimize
accumulation of errors in lengths
Subsidiary bases
6are made at intermediate stations to
control the error in azimuth
Astronomical observations
7Those triangulation stations are called
Laplace Stations.
8Purpose of Triangulation
• To establish the accurate control points for plane and geodetic
surveys of large areas
• To establish the accurate control points for photogrammetric surveys
• Accurate location of engineering works
9 • The triangulation survey is classified into three types:
Primary triangulation or First order triangulation
Secondary triangulation or Second order triangulation
Tertiary triangulation or Third order triangulation
10 • Highest grade of
triangulation system
• To determine the shape
and size of the earth's
surface
• Stations are generally
selected 16 km to 150 km
apart
Primary Triangulation
11• To connect two primary
triangulations to provide
control points closer
together than those of
primary triangulation
• For the densification of
horizontal control net
work
Secondary Triangulation
12 • To provide control
points between stations
of primary and second
order triangulation
• For the densification of
horizontal control for
topographical surveys
on various scales.
Tertiary Triangulation
13 The arrangement of the various triangles of a triangulation series
Layout of Triangulation
14 Three types of layout
(1) Simple triangles in chain
(2) Braced quadrilaterals in chain
(3) Centred triangles and polygons
15Used when control points are
provided in a narrow strip of
terrain such as a valley between
two ridges.
simple triangles in chain
16• Consists of figures containing
four corner stations and
observed diagonals
-the best
arrangement of triangles as it
provides a means of computing
the lengths of the sides using
different combination of the
sides and angles
Braced Quadrilaterals in chain
17Consists of figures containing
centered polygons and centered
triangles
generally are
quadrilaterals, pentagons, or
hexagons with central stations.
Centred Triangles and Polygons
18Factors to be consider in selecting a figure:
• Simple triangles - equilateral
• Braced quadrilaterals - squares
• Centered polygons - regular
• No angle of the figure, opposite a known side should be small
• angles of simple triangles - not be less than 45°
• quadrilaterals - no angle should be less than 30°.
• centered polygons - no angle should be less than 40°
• sides of the figures - should be of comparable length
19 Two methods of Layout for Primary Triangulation
Grid iron system
Centered system
20Usually run roughly along the meridians
(north-south) and along the
perpendiculars to the meridians (east
west) throughout the country
Adopted in India, Austria, Spain and
France
distance bet 2 chains - 150 km to 250 km
Grid iron system
21Whole area of the survey is
covered by a net work of
primary triangulation extending
outwards in all directions from
the initial base line
base line - laid at the centre of the country
Adopted in United Kingdom
Centered system
22 to provide a
surface mark with a permanent mark
buried below the surface on which a
target or instruments is to centred
over it
Should be bronze or copper marks
cemented into rock or concrete
surface
station marks