Geo-referencing, Ground Control Point
&
Monumentation
Coordinate Systems
A geographical coordinate system uses a three-dimensional spherical
surface to define locations on the earth.
Divides space into orderly structure of locations.
Two types: cartesian and angular (spherical)
© Paul Bolstad, GIS Fundamentals
Parallels and Meridians
Meridians are great circles of constant
longitude
Example is the prime meridian
Parallels are circles of constant latitude
Example is the equator
latitude (φ): angular distance from
equator
longitude (λ): angular distance from
standard meridian
New Delhi
Cuttack
Bhubaneswar
28°38' 7.1088” N 77°13' 29.856” E
20°27' 45.0756” N 85°52' 58.7622” E
20°17' 45.81132”N 85°49‘’ 28.34328” E
Setting up the Ground Control Network
The Survey of India is undertaking the task of establishing a ground control
point library (GCPL) for the entire country. In the first phase, 300 points of GCPs
have been established at a spacing of 200 to 300 km apart. 2200 points, at a
spacing of 30 to 40 km apart are to be established in the second phase of their
project. In the third phase of GCPL development, control points are planned to
be established at a distance of about 8 to 10 kms. GCPs at a distance of 8 to 10
km are likely to be of help in ground-truthing. States/UTs can consider
coordinating the establishment of ground control points for ground-truthing in
coordination with the Survey of India, in order to avoid duplication of efforts.
However, this need not hold up the work of survey and ground-truthing of
States/UTs.
Observation data of Control Points
Horizontal Datum: WGS-84 (i.e., the latest version of the
World Geodetic System standard for use in cartography)
Vertical Datum: MSL, i.e., the Mean Sea Level.
GROUND CONTROL POINT
An accurately surveyed coordinate location for a physical
feature that can be identified on the ground. Control points
are used in least-squares adjustments as the basis for
improving the spatial accuracy of all other points to which
they are connected.
One of various locations on a paper or digital map that has
known coordinates and is used to transform another
dataset—spatially coincident but in a different coordinate
system—into the coordinate system of the control point.
Control points are used in digitizing data from paper maps,
in geo-referencing both raster and vector data, and in
performing spatial adjustment operations such as rubber
sheeting.
Importance of Ground Control Points
•Reference Point
•Used for acquisition of Aerial Photography/
Satellite Imagery.
•Used for Survey of the Villages for digital and GIS
Mapping during Cadastral Survey.
•Used for Survey & Demarcation at post mapping
stage.
•Used for forest mining and other demarcations.
GROUND CONTROL POINT
GEOREFERENCING
Positioning of GCPs on the field : The GCPs are placed at every 16 KM x 16 KM and 4 Km X 4 KM called
as Primary Control Points (PCP) and Secondary Control Points (SCP) where DGPS observations are taken 12 hours at
PCPs and 2 hours at SCPs. There are also Tertiary Control Points (TCP), which are placed at every 1 KM x 1 KM and
Auxiliary Control Points (ACP), that are being placed as per requirement.
16KM.
PCP-1
SCP-1
PCP-2
4KM
4KM
SCP-2
SCP-3
SCP-4
SCP-5
PCP-4
PCP-3
GROUND CONTROL POINT (GCP)
ESTABLISHMENT - MONUMENTATION
MONUMENTATION PLANNING
OF
PRIMARY/
SECONDARY GROUND CONTROL POINTS (GCPs)
PRIMARY (16 km x 16 km grid)
SECONDARY( 4 Km x 4km grid )
MONUMENTATION OF GCPs
The monumentation of GCPs are intended to establish permanent markings
on the earth surface and to fix the corner positions so that the locations of
the surveyed lands may always be definitely known.
WHITE PAINT IS
TO BE APPLIED
AT 1.5 X 1.5 MT
STRIP
GCP MONUMENTATION
0.3mt
1.5 MT.
1.5 MT.
DGPS OBSERVATION OF GCP
SIMULTANEOUS GCP
OBSERVATIONS WITH SOI
BENCH MARK POINTS
Primary
Control Points
Secondary
Control Points
Ganjam District