180
(DMT), whose basic data structure is in the form of grid and TIN (triangular irregular network) (Li et al. 2005).
And the third way to represent the surface of the terrain is to use a volumetric
model, where the objects of space are represented by volumetric elements. One of
the typical examples is the use of voxels (volume elements, most often cubes or
prisms) of sufficiently small dimensions. This is analogous to the representation of
phenomena in digital raster images (or raster GIS), with the difference that digital
images are 2D displays. Namely, in these models, the terrain is presented as a body
composed of a set of interconnected voxels. Using this data model, tunnels, caves,
buildings and structures, settlements, etc. can be presented very easily. Another type
of volumetric models are models based on the representation of bodies in space
using the division of space into non-overlapping tetrahedra. This is analogous to
using TIN to represent phenomena in 2.5D models with functions of two variables.
Finally, it should be said that volumetric models are mainly represented in the presentation of infrastructure facilities and settlements, especially communications and
traffic. They are also used in geophysics, but are very rarely used for modelling terrain surfaces (Li et al. 2005).
6.6.1.1 Digital Terrain Modelling in Grid Form
Digital terrain modelling in the form of a grid implies the methodology and
technology of displaying the terrain over a set of points with known heights arranged
in a regular grid – a grid. In this way, the surface of the terrain is actually represented
by a 3D model called the digital elevation model (DEM) (Li et al. 2005). The
advantage of digital terrain modelling in the form of grid is reflected in:
• Application of simple algorithms for handling and analysis of height models
• Savings in terms of archiving, i.e. only the heights of points (pixels) are stored,
while their planimetric coordinates are implicitly given through the position of
the initial network element, network orientation in space, dimensions and position of the observed network element in the height matrix
• Use of algorithms, software tools and formats for archiving and data exchange
that are standardly used for raster GIS analysis and digital image processing
• Realization of simple algebraic operations on grid elements, the combination of
which can perform very complex analyses, including advanced data compression
and record pyramids for representing the terrain in other (different) resolutions
6.6.1.2 Digital Terrain Modelling in the Form of TIN
Digital data modelling in the form of TIN is represented in many practical solutions
and software tools for the formation and analysis of 3D terrain models. When modelling terrain in the form of TIN, the vertices (nodes) of triangles are points with
known heights (Li et al. 2005). The triangles are interconnected so that they better
R. Šajn et al.
(DMT), whose basic data structure is in the form of grid and TIN (triangular irregular network) (Li et al. 2005).
And the third way to represent the surface of the terrain is to use a volumetric
model, where the objects of space are represented by volumetric elements. One of
the typical examples is the use of voxels (volume elements, most often cubes or
prisms) of sufficiently small dimensions. This is analogous to the representation of
phenomena in digital raster images (or raster GIS), with the difference that digital
images are 2D displays. Namely, in these models, the terrain is presented as a body
composed of a set of interconnected voxels. Using this data model, tunnels, caves,
buildings and structures, settlements, etc. can be presented very easily. Another type
of volumetric models are models based on the representation of bodies in space
using the division of space into non-overlapping tetrahedra. This is analogous to
using TIN to represent phenomena in 2.5D models with functions of two variables.
Finally, it should be said that volumetric models are mainly represented in the presentation of infrastructure facilities and settlements, especially communications and
traffic. They are also used in geophysics, but are very rarely used for modelling terrain surfaces (Li et al. 2005).
6.6.1.1 Digital Terrain Modelling in Grid Form
Digital terrain modelling in the form of a grid implies the methodology and
technology of displaying the terrain over a set of points with known heights arranged
in a regular grid – a grid. In this way, the surface of the terrain is actually represented
by a 3D model called the digital elevation model (DEM) (Li et al. 2005). The
advantage of digital terrain modelling in the form of grid is reflected in:
• Application of simple algorithms for handling and analysis of height models
• Savings in terms of archiving, i.e. only the heights of points (pixels) are stored,
while their planimetric coordinates are implicitly given through the position of
the initial network element, network orientation in space, dimensions and position of the observed network element in the height matrix
• Use of algorithms, software tools and formats for archiving and data exchange
that are standardly used for raster GIS analysis and digital image processing
• Realization of simple algebraic operations on grid elements, the combination of
which can perform very complex analyses, including advanced data compression
and record pyramids for representing the terrain in other (different) resolutions
6.6.1.2 Digital Terrain Modelling in the Form of TIN
Digital data modelling in the form of TIN is represented in many practical solutions
and software tools for the formation and analysis of 3D terrain models. When modelling terrain in the form of TIN, the vertices (nodes) of triangles are points with
known heights (Li et al. 2005). The triangles are interconnected so that they better
R. Šajn et al.