High Resolution 1:10,000 scale Mapping Strategy of Multi ... - NDMA

3. Block Adjustment
As it has been proposed to use digital photogrammetry techniques in
generation of the large scale maps, Survey of India will carry out block adjustment for
mapping and generate digital terrain model. Block adjustment is done to reference
the satellite imageries with the ground and bring all the satellite imageries in the
same national reference frame. Digital Terrain Model is created to remove the
distortion due to height variation from the satellite imageries and to create orthoimages.
DEM is a different product which can be subsequently used for terrain
analysis and it can also be used as an input in GIS data in unrestricted zone. The
fundamental concepts involved in block triangulation, DEM generation and ortho
rectification are detailed below:
Block Triangulation
Block triangulation is the process of establishing a mathematical relationship
between the imageries contained in a project, the sensor model, and the ground.
Once the relationship has been defined, accurate imagery and geographic
information concerning the Earth’s surface can be created.
The information resulting from block triangulation is required as input for the
orthorectification, DEM creation, and stereopair creation processes.
With the advent of digital photogrammetry, classic aerial triangulation has been
extended to provide greater functionality. Mathematical technique known as block
adjustment provides three primary functions:
• Block adjustment determines the position and orientation sensor model in a
project as they existed at the time of image exposure. The resulting
parameters are referred to as exterior orientation parameters. Block
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