Digital Terrain Modeling
(PBW 5024)
AHMED, Wael (PhD)
Spring 2024
Contact Information
• Instructor: Dr. Wael AHMED
• Office: 32404
• Mobile: (+2)01118670361
• Email: dief_wael@eng.cu.edu.eg
• Lectures: Saturday (2:00 pm- 3:30 pm)
• Office Hours: Flexible
PBW 5024
Course Objectives
• Understand key principles of DTM creation, analysis, and
application,
• Evaluate and compare methods to create accurate and detailed
DTMs,
• Explain fundamentals of LIDAR and data collection procedures,
• Process LIDAR datasets, including data geo-referencing,
filtering, and modeling,
• Perform evaluation through error analysis.
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Grading System
• Credit hours: 3
• Course work: 40%
• Assignments, Presentation
• Final Exam: 60%
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Terminology
• Digital Terrain Model (DTM).
• Digital Elevation Model (DEM).
• Digital Height Model (DHM).
• Digital Ground Model (DGM).
• Digital Terrain Elevation Data (DTED).
• Digital Surface Model (DSM).
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Digital Elevation Models (DEMs)
A digital elevation model (DEM) is a 3D computer
graphics representation of elevation data to represent features.
In some references, it is called Digital Height Models (DHMs).
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Digital Terrain Model (DTM)
A digital terrain model is a bare-earth raster grid referenced
to a vertical datum
The built (power lines, buildings and towers) and
natural (trees and other types of vegetation)
aren’t included in a DTM
When you filter out non-ground points such as bridges and
roads, you get a smooth digital elevation model
A bare-earth elevation model is particularly useful in
hydrology, soils and land use planning
© GIS Geography 2018 PBW 5024
Digital Terrain Model (DTM)
➢Digital Terrain Models (DTMs) are a type of raster GIS layer
➢In a DTM, each cell of raster GIS layer has a value corresponding to its
elevation (z-values at regularly spaced intervals)
➢DTM data files contain the elevation of the terrain over a specified area,
usually at a fixed grid interval over the “Bare Earth”
➢The intervals between each of the grid points will always be referenced to
some geographical coordinate system (latitude and longitude or UTM
(Universal Transverse Mercator) coordinate systems (Easting and Northing)
➢For more detailed the information in DTM data file, it is necessary that grid
points are closer together
➢The details of the peaks and valleys in the terrain will be better modeled
with small grid spacing than when the grid intervals are very large
© GIS Recourses 2016 PBW 5024
Digital Surface Model (DSM)
➢Digital Surface Model (DSM) represents
the elevations of the reflective surfaces of trees,
buildings, and other features elevated
above the “Bare Earth”
➢A DSM is useful in:
➢ 3D modeling for telecommunications,
➢Runway approach zone encroachment: In aviation, DSMs can
determine runway obstructions in the approach zone
➢Vegetation management: Along a transmission line, DSMs can see
where and how much vegetation is encroaching
➢View obstruction: Urban planners use DSM to check how a
proposed building would affect the view
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DSM vs DTM
DTM
DSM
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DTM Application Domains
❑Civil Engineering:
• Cut-and-fill problems involved with road design.
• Site planning.
• Volumetric calculations in building dams and reservoirs
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DTM Application Domains
➢ Road design
Horizontal alignment Vertical alignment
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DTM Application Domains
➢ Road design
Ref: Digital Terrain Models by M. Varshosaz
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DTM Application Domains
❑Earth Sciences:
• Drainage basin network development and delineation.
• Hydrological run-off modeling.
• Geo-morphological simulation and classification.
• Geological mapping.
• Generating slope and aspect maps.
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DTM Application Domains
• Analysis and interpretation of terrain morphology
• 3D visualization and Flight simulation
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DTM Application Domains
❑Planning and Resource Management:
• The management of natural resources.
• Site location.
• Support of image classification in remote sensing by DTM derivatives.
• Geometric and radiometric correction of remote sensing images
• Wind flow and pollution dispersion models
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❑Terrain Mapping
➢ Contouring is most common method for terrain mapping.
➢Contour lines connect points of equal elevation (isolines).
➢Arrangement of contour lines reflect topography.
➢Vertical profile shows changes in elevation along a line.
❑Terrain Analysis
➢Slope measures the rate of change of elevation at a surface location.
➢Aspect is the directional measure of the slope.
➢Terrain Analysis is important for analyzing and visualizing landform
➢characteristics and rock-mass properties.
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Digital Elevation Modeling (DEM)
vs.
Digital Terrain Modeling (DTM)
• DEM is the digital representation of ACTUAL topographic relief. It
accounts the height of the buildings or vegetation canopy. It is
generated from stereoscopic image pair or interferometric data.
• DTM is the digital representation of TERRAIN height. It does not
account the height of the buildings or vegetation canopy rather the
height of the terrain. It is generated from topographic maps.
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Representation of DTM
➢Vector Mode.
Contour Lines.
➢TIN Mode.
Triangulated Irregular Network.
➢Raster Mode.
Regular Grid.
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Relief Representation in TIN Mode
➢The only method capable of physically modelling the terrain surface.
➢The modelling is correct only if it takes into account terrain break lines and spot
heights.
➢A regular grid or contour lines can be easily derived from triangulation.
▪ Series of non-overlapping triangles.
• Elevation values are stored at nodes.
• Irregular distribution.
Borders are a problem …
Go beyond study area and clip to make the best.
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Relief Representation in Raster Mode
➢The rectangular or square grid can not model the terrain surface.
➢Since there are no links, the shape can not be described
e.g., where the river flows or how the crest aligns.
➢Hides low reliefs; gives an incomplete description of relief.
➢Easy for processing and handling in computers.
Grid interval must be compatible with project requirements and the original data accuracy.
DTM represents a single altitude value for each cell.
DTM should be compatible with the application. For example, in case of drainage line mapping,
minimum cell altitude and in case of ridge-line mapping maximum altitude should be taken in the
DTM. PBW 5024
Grid vs TIN
➢Different algorithms and type of output.
➢Can be converted from TIN to grid or grid to TIN.
➢TIN has flexibility of input sources: DEM, break lines, contour lines.
GPS data and survey data as well as user added elevation points.
➢Elevation grid is fixed with a given cell size.
➢Computational efficiency is more in grid method than in TIN method.
➢TIN gives sharper image as it physically models the terrain than that
in grid method.
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DEMs and TINs
DEM with sample points TINs based on same sample points
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Advantages/disadvantages
DEMs:
• accept data direct from digital altitude matrices
• must be resampled if irregular data used
• may miss complex topographic features
• may include redundant data in low relief areas
• less complex and CPU intensive
TINs:
• accept randomly sampled data without resampling
• accept linear features such as contours and break lines (ridges and troughs)
• accept point features (spot heights and peaks)
• vary density of sample points according to terrain complexity
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Assignment 1
• Describe in detail the difference between:
• DSM and DTM,
• DEM and TIN.
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