Georeferencing services

1. SBL GSS Division
Georeferencing Service
By
Venugopalan Nair

2. Georeferencing
SBL through its varied geo spatial services is in forefront to full fill the
requirements of all of its clients. Geo referencing is one such service SBL
provides. Geo referencing means bringing maps and images in to a real world
coordinate system. Satellite and other kinds of images and scanned maps are
devoid of any coordinate information in its raw form and hence cannot used for
any of the geo spatial purpose. Some of the satellite images are loosely geo
referenced when it is procured. Here also positional accuracy is a big issue.
So geo referencing is the primary pre requisite for the creation of any kind of
geo spatial data base creation. For scanned maps geo referencing means
bringing to the geo spatial frame work. For satellite images geo referencing
means applying geometric correction to the images. Assigning a suitable
project is always an associated activity in geo referencing. So geo referencing
is not only bringing the maps and images to the coordinate framework, it also
involves with assigning a suitable projection so that maps and images will be of
real world coordinates. A geo referenced map or image will open in its correct
spatial location and can be used with similar other geo referenced maps for
various overlay analysis. Hence geo referencing is a positional correction
applied in x, y direction of the maps and images. Ortho rectification is a refined
form of geo referencing where relief displacement will also be taken care so
that images will be correct with respect to x, y and z planes.

3. Geo referencing is a basic function available in almost all geo spatial software platforms. The major
activities involved are incorporation of ground control points, re projection and re sampling.
Ground control points are those points whose coordinate information (latitude and longitude
values) were known prior hand and is identifiable in maps and images. Ground control points can
be taken from printed graticule values on maps, or can be surveyed using precision instruments
such as DGPS and can be taken from a pre geo referenced map or image. A minimum number of 5
GCP values are required for geo referencing. Based on the accuracy requirement number of GCPs
and type of GCPs can be determined. Once the ground control points are placed, using the
software algorithms we can re project and re sample the maps or images. Various complex
statistical methods and transformational equations were used for the re sampling the images to its
real world coordinates. During the process each and every pixel of the maps and images will be re
positioned with respect to the GCP and methods used for the purpose and finally a geo referenced
maps or image can be generated. Accuracy of the geo referencing can always be obtained through
RMSE error for the GCPs used in the process. Hence it is very much a quality controlled activity
where very high positional accuracy can be obtained.SBL is capable of handling images and maps
in huge numbers for geo referencing and allied acidities.
Georeferencing

4. Georeferencing

5. Georeferencing

6. Carnival Infopark - Phase II
Kakkanad, Cochin,
India – 682030

7. Carnival Infopark - Phase II
Kakkanad, Cochin,
India – 682030