This document defines and describes Digital Elevation Models (DEMs). It discusses that DEMs are 3D representations of land surface elevation from various data sources. There are two main types of DEMs - raster and vector (TIN). Data can be captured through remote sensing, photogrammetry, or land surveys. Free global DEMs are available from sources like SRTM, ASTER, and ALOS. DEMs have many applications including terrain analysis, hydrology, mapping, and more.
Digital Elevation Model (DEM) is the digital representation of the land surface elevation with respect to any reference datum. DEM is frequently used to refer to any digital representation of a topographic surface. DEM is the simplest form of digital representation of topography. GIS applications depend mainly on DEMs, today.
Digital Elevation Model (DEM) is the digital representation of the land surface elevation with respect to any reference datum. DEM is frequently used to refer to any digital representation of a topographic surface. DEM is the simplest form of digital representation of topography. GIS applications depend mainly on DEMs, today.
RS & GIS, Image Interpretation, Methods of Image interpretation, Types of interpretation, Factors governing image interpretation, Activities to interpret image, Sensors, Role of sensors in Image derivation, Aerial Photography, LISS-3, Image characteristics, Special characteristics, Shadow, Texture, Pattern, associated features in images
Iirs overview -Remote sensing and GIS application in Water Resources ManagementTushar Dholakia
Remote sensing and GIS application in Water Resources Management- By S.P. Aggarval spa@iirs.gov.in Indian Institute of Remote sensing ISRO, Department of space, Dehradun
Types of Platforms
1. Airbrone Platforms
2. Spacebrone Platforms
Platforms are Vital Role in remote sensing data acquisition
Necessary to correct the position the remote sensors that collect data from the objects of interest
DEFINITION :
GIS is a powerful set of tools for collecting, storing , retrieving at will, transforming and displaying spatial data from the real world for a particular set of purposes
APPLICATION AREAS OF GIS
Agriculture
Business
Electric/Gas utilities
Environment
Forestry
Geology
Hydrology
Land-use planning
Local government
Mapping
11. Military
12. Risk management
13. Site planning
14. Transportation
15. Water / Waste water industry
COMPONENTS OF GIS
DATA INPUT
SPATIAL DATA MODEL
Data Model:
It describes in an abstract way how the data is represented in an information system or in DBMS
Spatial Data Model :
The models or abstractions of reality that are intended to have some similarity with selected aspects of the real world
Creation of analogue and digital spatial data sets involves seven levels of model development and abstraction
SPATIAL DATA MODEL
Conceptual model : A view of reality
Analog model : Human conceptualization leads to analogue abstraction
Spatial data models : Formalization of analogue abstractions without any conventions
Database model : How the data are recorded in the computer
Physical computational model : Particular representation of the data structures in computer memory
Data manipulation model : Accepted axioms and rules for handling the data
SPATIAL DATA MODEL
SPATIAL DATA MODEL
Objects on the earth surface are shown as continuous and discrete objects in spatial data models
Types of data models
Raster data model
vector data models
RASTER DATA MODEL
Basic Elements :
Extent
Rows
Columns
Origin
Orientation
Resolution: pixel = grain = grid cell
Ex: Bit Map Image (BMP),Joint Photographic Expert Group (JPEG), Portable Network Graphics(PNG) etc
RASTER DATA MODEL
VECTOR DATA MODEL
Basic Elements:
Location (x,y) or (x,y,z)
Explicit, i.e. pegged to a coordinate system
Different coordinate system (and precision) require different values
o e.g. UTM as integer (but large)
o Lat, long as two floating point numbers +/-
Points are used to build more complex features
Ex: Auto CAD Drawing File(DWG), Data Interchange(exchange) File(DXF), Vector Product Format (VPF) etc
VECTOR DATA MODEL
RASTER vs VECTORRaster is faster but Vector is corrector
TESSELLATIONS OF CONTINUOUS FIELDS
Triangular Irregular Network: (TIN)
TIN is a vector data structure for representing geographical information that is continuous
Digital elevation model
TIN is generally used to create Digital Elevation Model (DEM)
DIGITAL ELEVATION MODEL
DATA STRUCTURES
Data structure tells about how the data is stored
Data organization in raster data structures
Each cell is referenced directly
Each overlay Is referenced directly
Each mapping unit is referenced directly
Each overlay is separate file with general header
International Journal of Modern Engineering Research (IJMER) is Peer reviewed, online Journal. It serves as an international archival forum of scholarly research related to engineering and science education.
International Journal of Modern Engineering Research (IJMER) covers all the fields of engineering and science: Electrical Engineering, Mechanical Engineering, Civil Engineering, Chemical Engineering, Computer Engineering, Agricultural Engineering, Aerospace Engineering, Thermodynamics, Structural Engineering, Control Engineering, Robotics, Mechatronics, Fluid Mechanics, Nanotechnology, Simulators, Web-based Learning, Remote Laboratories, Engineering Design Methods, Education Research, Students' Satisfaction and Motivation, Global Projects, and Assessment…. And many more.
RS & GIS, Image Interpretation, Methods of Image interpretation, Types of interpretation, Factors governing image interpretation, Activities to interpret image, Sensors, Role of sensors in Image derivation, Aerial Photography, LISS-3, Image characteristics, Special characteristics, Shadow, Texture, Pattern, associated features in images
Iirs overview -Remote sensing and GIS application in Water Resources ManagementTushar Dholakia
Remote sensing and GIS application in Water Resources Management- By S.P. Aggarval spa@iirs.gov.in Indian Institute of Remote sensing ISRO, Department of space, Dehradun
Types of Platforms
1. Airbrone Platforms
2. Spacebrone Platforms
Platforms are Vital Role in remote sensing data acquisition
Necessary to correct the position the remote sensors that collect data from the objects of interest
DEFINITION :
GIS is a powerful set of tools for collecting, storing , retrieving at will, transforming and displaying spatial data from the real world for a particular set of purposes
APPLICATION AREAS OF GIS
Agriculture
Business
Electric/Gas utilities
Environment
Forestry
Geology
Hydrology
Land-use planning
Local government
Mapping
11. Military
12. Risk management
13. Site planning
14. Transportation
15. Water / Waste water industry
COMPONENTS OF GIS
DATA INPUT
SPATIAL DATA MODEL
Data Model:
It describes in an abstract way how the data is represented in an information system or in DBMS
Spatial Data Model :
The models or abstractions of reality that are intended to have some similarity with selected aspects of the real world
Creation of analogue and digital spatial data sets involves seven levels of model development and abstraction
SPATIAL DATA MODEL
Conceptual model : A view of reality
Analog model : Human conceptualization leads to analogue abstraction
Spatial data models : Formalization of analogue abstractions without any conventions
Database model : How the data are recorded in the computer
Physical computational model : Particular representation of the data structures in computer memory
Data manipulation model : Accepted axioms and rules for handling the data
SPATIAL DATA MODEL
SPATIAL DATA MODEL
Objects on the earth surface are shown as continuous and discrete objects in spatial data models
Types of data models
Raster data model
vector data models
RASTER DATA MODEL
Basic Elements :
Extent
Rows
Columns
Origin
Orientation
Resolution: pixel = grain = grid cell
Ex: Bit Map Image (BMP),Joint Photographic Expert Group (JPEG), Portable Network Graphics(PNG) etc
RASTER DATA MODEL
VECTOR DATA MODEL
Basic Elements:
Location (x,y) or (x,y,z)
Explicit, i.e. pegged to a coordinate system
Different coordinate system (and precision) require different values
o e.g. UTM as integer (but large)
o Lat, long as two floating point numbers +/-
Points are used to build more complex features
Ex: Auto CAD Drawing File(DWG), Data Interchange(exchange) File(DXF), Vector Product Format (VPF) etc
VECTOR DATA MODEL
RASTER vs VECTORRaster is faster but Vector is corrector
TESSELLATIONS OF CONTINUOUS FIELDS
Triangular Irregular Network: (TIN)
TIN is a vector data structure for representing geographical information that is continuous
Digital elevation model
TIN is generally used to create Digital Elevation Model (DEM)
DIGITAL ELEVATION MODEL
DATA STRUCTURES
Data structure tells about how the data is stored
Data organization in raster data structures
Each cell is referenced directly
Each overlay Is referenced directly
Each mapping unit is referenced directly
Each overlay is separate file with general header
International Journal of Modern Engineering Research (IJMER) is Peer reviewed, online Journal. It serves as an international archival forum of scholarly research related to engineering and science education.
International Journal of Modern Engineering Research (IJMER) covers all the fields of engineering and science: Electrical Engineering, Mechanical Engineering, Civil Engineering, Chemical Engineering, Computer Engineering, Agricultural Engineering, Aerospace Engineering, Thermodynamics, Structural Engineering, Control Engineering, Robotics, Mechatronics, Fluid Mechanics, Nanotechnology, Simulators, Web-based Learning, Remote Laboratories, Engineering Design Methods, Education Research, Students' Satisfaction and Motivation, Global Projects, and Assessment…. And many more.
A geographic information system (GIS) is a computer-based tool for mapping and analyzing features and events on earth. On the other hand, remote sensing is the science of collecting data regarding an object or a phenomenon without any physical contact with the object
Surveying for Civil engineering is a
particular type of surveying known as "land surveying", it is the
detailed study or inspection, as by gathering information through
observations, measurements in the field, questionnaires, or
research of legal instruments, and data analysis in the support of
planning, designing, and establishing of property boundaries.
Land surveying can include associated services such as mapping
and related data accumulation, construction layout surveys,
precision measurements of length, angle, elevation, area, and
volume, as well as horizontal and vertical control surveys, and
the analysis and utilization of land survey data. Surveyors use
various tools to do their work successfully and accurately, such
as total stations, robotic total stations, GPS receivers, prisms, 3D
scanners, radio communicators, handheld tablets, digital levels,
and surveying software.
Survey data can be directly entered into a GIS from digital
data collection systems on survey instruments. When data is
captured, the user should consider if the data should be captured
with either a relative accuracy or absolute accuracy, since this
could not only influence how information will be interpreted but
also the cost of data captured.
In this paper GIS maps were developed depending on the
field surveying data made for a two traverses. First one has ribs
less than 50m length and the other larger than 50m. Each
traverse is holding five times using five equipments and
instruments: Tape, Level, Digital level, Digital theodolite and
Laser tape. Also those maps were drawn by using both of ACAD
and ArcView softwares. Then a detail surveying map was
produced. The precision was computed for both traverses in each
method. Its value is range from 1/140 to 1/10000.
Laser ScanningLaser scanning is an emerging data acquisition techn.pdfanjaniar7gallery
Laser Scanning
Laser scanning is an emerging data acquisition technology that has remarkably broadened its
application field and has been a serious competitor to other surveying techniques. Due to rapid
technological development, the increased accuracy of global positioning systems and improving
demands to even more accurate digital surface models, airborne laser scanning showed
significant development in the 1990s.
Somewhat later terrestrial laser scanning became a reasonable alternative method in many kinds
of applications that previously by ground based surveying or close-range photogrammetry.
1 Airborne laser scanning
Airborne laser scanning is an active remote sensing technology that is able to rapidly collect data
from huge areas. The resulted dataset can be the base of digital surface and elevation models.
Airborne laser scanning is often coupled with airborne imagery, therefore the point clouds and
images can be fused resulting enhanced quality 3D product.
The basic principle is as follows: the sensor emits a laser pulse through the terrain in a
predefined direction and receives the reflected laser beam. Knowing the speed of light, the
distance of the object can be calculated, see Figure 1.
Figure 1.: Time of flight laser range measurement [2]
Airborne LiDAR systems are composed by the following subsystems:
The components are shown in Figure 2
Figure 2.: Principle of airborne LiDAR [2]
2. Sensors, equipment
Sensors can be distinguished based on the scanning method, i.e. how the laser beam is directed
through the surface. The four most widely used sensor types are shown in Figure 4.2.3.
Figure .3: Scanning mechanisms [1]
As it is clearly seen in Figure 3, different kinds of mechanisms are applied by the different types
of sensors; each has its advantages and shortcomings, e.g. number of moving parts, type of
rotation etc. that lead to different kinds of error sources.
The capabilities (repetition rate, scan frequency, scan angle, point density) of the above scanners
are very similar; the main difference lies in the scanning pattern, as seen in Figure 4. The most
widely used oscillating mirror scanners produce the zigzag pattern. Spacing along the line
depends on the pulse rate and scanning frequency, while spacing along the flight direction
depends on the flying speed. To avoid too wide spacing of points along flight direction, LiDAR
flights are usually slower (e.g. at 60-80 m/sec) compared to that of photogrammetric flights
(even 120-160 m/sec). Careful planning of the measurement results in rather homogenous
density, however, due to technical and microelectronic reasons (regarding the operating
mechanism of the mirror, especially in case of oscillating mirrors), higher point density can be
observed at the edges of the scan swath. Previously, critics were addressed to the fixed optic
scanners, i.e. the parallel scan lines along the flight direction can miss sizeable objects, but
vendors successfully responded and modified the mechanis.
Introduction to Data Science, Prerequisites (tidyverse), Import Data (readr), Data Tyding (tidyr),
pivot_longer(), pivot_wider(), separate(), unite(), Data Transformation (dplyr - Grammar of Manipulation): arrange(), filter(),
select(), mutate(), summarise()m
Data Visualization (ggplot - Grammar of Graphics): Column Chart, Stacked Column Graph, Bar Graph, Line Graph, Dual Axis Chart, Area Chart, Pie Chart, Heat Map, Scatter Chart, Bubble Chart
Overview and about R, R Studio Installation, Fundamentals of R Programming: Data Structures and Data Types, Operators, Control Statements, Loop Statements, Functions,
Descriptive Analysis using R: Maximum, Minimum, Range, Mean, Median and Mode, Variance, Standard Deviation, Quantiles, IQR, Summary
Introduction to Statistics -
Sampling Techniques, Types of Statistics, Descriptive Statistics,
Inferential Statistics,
Variables and Types of Data: Qualitative, Quantitative, Discrete,
Continuous, Organizing and Graphing Data: Qualitative Data, Quantitative Data
1. Angular Components:
Component Configuration, Building a Template, Using Constructors, Using External Templates, Angular Routing to Single Page Application (SPA)
2. Data Binding:
Introduction, Interpolation, Property Binding, Attribute Binding, Class Binding, Style Binding, Event Binding, Two-way Binding.
Topics:
1. Introduction to GIS
2. Components of GIS
3. Types of Data
4. Spatial Data
5. Non-Spatial Data
6. GIS Operations
7. Coordinate Systems
8. Datum
9. Map Projections
10. Raster Data Compression Techniques
11. GIS Software
12. Free GIS Data Resources
Topics:
1. Mapping Concepts
2. Analysis with paper based Maps
3. Limitations of Paper based Maps
4. Computer Aided Cartography History and Development
5. GIS Definition
6. Advantage of Digital Maps
Topics:
1. Introduction to Fluid Dynamics
2. Surface and Body Forces
3. Equations of Motion
- Reynold’s Equation
- Navier-Stokes Equation
- Euler’s Equation
- Bernoulli’s Equation
- Bernoulli’s Equation for Real Fluid
4. Applications of Bernoulli’s Equation
5. The Momentum Equation
6. Application of Momentum Equations
- Force exerted by flowing fluid on pipe bend
- Force exerted by the nozzle on the water
7. Measurement of Flow Rate
a). Venturimeter
b). Orifice Meter
c). Pitot Tube
8. Measurement of Flow Rate in Open Channels
a) Notches
b) Weirs
1. Introduction to Kinematics
2. Methods of Describing Fluid Motion
a). Lagrangian Method
b). Eulerian Method
3. Flow Patterns
- Stream Line
- Path Line
- Streak Line
- Streak Tube
4. Classification of Fluid Flow
a). Steady and Unsteady Flow
b). Uniform and Non-Uniform Flow
c). Laminar and Turbulent Flow
d). Rotational and Irrotational Flow
e). Compressible and Incompressible Flow
f). Ideal and Real Flow
g). One, Two and Three Dimensional Flow
5. Rate of Flow (Discharge) and Continuity Equation
6. Continuity Equation in Three Dimensions
7. Velocity and Acceleration
8. Stream and Velocity Potential Functions
E-Waste or Electronic Waste may be defined as discarded computers, office electronic equipment, entertainment device electronics, mobile phones, television sets and refrigerators. This definition includes used electronics which are destined for reuse, resale, salvage, recycling, or disposal.
Biomedical Waste is any kind of waste that contains infectious material (or material that’s potentially infectious). This definition includes waste generated by healthcare facilities like physician’s offices, hospitals, dental practices, laboratories, medical research facilities, and veterinary clinics
Palestine last event orientationfvgnh .pptxRaedMohamed3
An EFL lesson about the current events in Palestine. It is intended to be for intermediate students who wish to increase their listening skills through a short lesson in power point.
Students, digital devices and success - Andreas Schleicher - 27 May 2024..pptxEduSkills OECD
Andreas Schleicher presents at the OECD webinar ‘Digital devices in schools: detrimental distraction or secret to success?’ on 27 May 2024. The presentation was based on findings from PISA 2022 results and the webinar helped launch the PISA in Focus ‘Managing screen time: How to protect and equip students against distraction’ https://www.oecd-ilibrary.org/education/managing-screen-time_7c225af4-en and the OECD Education Policy Perspective ‘Students, digital devices and success’ can be found here - https://oe.cd/il/5yV
The Indian economy is classified into different sectors to simplify the analysis and understanding of economic activities. For Class 10, it's essential to grasp the sectors of the Indian economy, understand their characteristics, and recognize their importance. This guide will provide detailed notes on the Sectors of the Indian Economy Class 10, using specific long-tail keywords to enhance comprehension.
For more information, visit-www.vavaclasses.com
Ethnobotany and Ethnopharmacology:
Ethnobotany in herbal drug evaluation,
Impact of Ethnobotany in traditional medicine,
New development in herbals,
Bio-prospecting tools for drug discovery,
Role of Ethnopharmacology in drug evaluation,
Reverse Pharmacology.
This is a presentation by Dada Robert in a Your Skill Boost masterclass organised by the Excellence Foundation for South Sudan (EFSS) on Saturday, the 25th and Sunday, the 26th of May 2024.
He discussed the concept of quality improvement, emphasizing its applicability to various aspects of life, including personal, project, and program improvements. He defined quality as doing the right thing at the right time in the right way to achieve the best possible results and discussed the concept of the "gap" between what we know and what we do, and how this gap represents the areas we need to improve. He explained the scientific approach to quality improvement, which involves systematic performance analysis, testing and learning, and implementing change ideas. He also highlighted the importance of client focus and a team approach to quality improvement.
How to Split Bills in the Odoo 17 POS ModuleCeline George
Bills have a main role in point of sale procedure. It will help to track sales, handling payments and giving receipts to customers. Bill splitting also has an important role in POS. For example, If some friends come together for dinner and if they want to divide the bill then it is possible by POS bill splitting. This slide will show how to split bills in odoo 17 POS.
The Roman Empire A Historical Colossus.pdfkaushalkr1407
The Roman Empire, a vast and enduring power, stands as one of history's most remarkable civilizations, leaving an indelible imprint on the world. It emerged from the Roman Republic, transitioning into an imperial powerhouse under the leadership of Augustus Caesar in 27 BCE. This transformation marked the beginning of an era defined by unprecedented territorial expansion, architectural marvels, and profound cultural influence.
The empire's roots lie in the city of Rome, founded, according to legend, by Romulus in 753 BCE. Over centuries, Rome evolved from a small settlement to a formidable republic, characterized by a complex political system with elected officials and checks on power. However, internal strife, class conflicts, and military ambitions paved the way for the end of the Republic. Julius Caesar’s dictatorship and subsequent assassination in 44 BCE created a power vacuum, leading to a civil war. Octavian, later Augustus, emerged victorious, heralding the Roman Empire’s birth.
Under Augustus, the empire experienced the Pax Romana, a 200-year period of relative peace and stability. Augustus reformed the military, established efficient administrative systems, and initiated grand construction projects. The empire's borders expanded, encompassing territories from Britain to Egypt and from Spain to the Euphrates. Roman legions, renowned for their discipline and engineering prowess, secured and maintained these vast territories, building roads, fortifications, and cities that facilitated control and integration.
The Roman Empire’s society was hierarchical, with a rigid class system. At the top were the patricians, wealthy elites who held significant political power. Below them were the plebeians, free citizens with limited political influence, and the vast numbers of slaves who formed the backbone of the economy. The family unit was central, governed by the paterfamilias, the male head who held absolute authority.
Culturally, the Romans were eclectic, absorbing and adapting elements from the civilizations they encountered, particularly the Greeks. Roman art, literature, and philosophy reflected this synthesis, creating a rich cultural tapestry. Latin, the Roman language, became the lingua franca of the Western world, influencing numerous modern languages.
Roman architecture and engineering achievements were monumental. They perfected the arch, vault, and dome, constructing enduring structures like the Colosseum, Pantheon, and aqueducts. These engineering marvels not only showcased Roman ingenuity but also served practical purposes, from public entertainment to water supply.
Instructions for Submissions thorugh G- Classroom.pptxJheel Barad
This presentation provides a briefing on how to upload submissions and documents in Google Classroom. It was prepared as part of an orientation for new Sainik School in-service teacher trainees. As a training officer, my goal is to ensure that you are comfortable and proficient with this essential tool for managing assignments and fostering student engagement.
The Art Pastor's Guide to Sabbath | Steve ThomasonSteve Thomason
What is the purpose of the Sabbath Law in the Torah. It is interesting to compare how the context of the law shifts from Exodus to Deuteronomy. Who gets to rest, and why?
2. Topics
1. What is DEM?
2. Use of DEM
3. Types of DEM
a) Raster DEM
b) Vector DEM – Triangular Irregular networks (TIN)
4. Data Capture Methods
a) Remote Sensing
b) Aerial Photogrammetry
c) Land Surveying and Contour Maps
5. Generation of DEM/ Source of DEM
a) SRTM
b) ASTER
c) JAXA’s Global ALOS 3D World
d) NRSA Bhuvan’s CartoDEM
6. Application of DEM
3. What is DEM?
A Digital Elevation Model (DEM), also referred to as the Digital Terrain
Model (DTM) is a digital model or three dimensional (3D)
representation of the land surface elevation with respect to any
reference datum.
Technically a DEM contains only the elevation information of the
surface, free of vegetation, buildings and other non ground objects
with reference to a datum such as Mean Sea Level (MSL).
Reference: http://charim.net/datamanagement/32
4. Uses of DEM?
The following are most useful Parameters in depicting geological information using DEM:
1. Slope: Displays the grade of steepness expressed in degrees or as percent slope. This image can
reveal structural lineaments, fault scarps, fluvial terrace scarps, etc.
2. Aspect: Identifies the down-slope direction. Aspect images may enhance landforms such as
fluvial networks, alluvial fans, faceted fault related scarps, etc.
3. Shaded topographic relief or hill-shading: This image depicts relief by simulating the effect of
the sun's illumination on the terrain. The direction and the altitude of the illumination can be changed
in order to emphasize faults, lineaments, etc.
4. Flow direction: Shows the direction of flow by finding the direction of the steepest descent or
maximum drop. This DEM derived surface depicts the drainage.
5. Basin/ Watershed: Function that uses a grid of flow direction (output of flow direction) to
determine the contributing area.
5.
6.
7.
8. Types of DEM
DEMs are generated by using the elevation information from several points
spaced at regular or irregular intervals.
The DEM could be acquired through techniques such as photogrammetry,
LiDAR, land surveying, etc. DEMs are commonly built using data collected
using remote sensing techniques, but they may also be built from land
surveying.
DEMs use different structures to acquire or store the elevation
information from various sources. Three main type of structures used are
the following:
1. Raster DEM - Regular square grids
2. Vector DEM - Triangular irregular networks (TIN)
9.
10. Triangular Irregular Network (TIN)
Triangular irregular networks (TIN) are a form of vector-based digital
geographic data and are constructed by triangulating a set of vertices (points).
The vertices are connected with a series of edges to form a network of
triangles. There are different methods of interpolation to form these triangles,
such as Delaunay triangulation or distance ordering.
11. Data Capture
1. Data Capture through Remote Sensing:
One powerful technique for generating DEM is interferometric synthetic
aperture radar where two passes of a radar satellite (such as RADARSAT-1 or
TerraSAR-X or Cosmo SkyMed), or a single pass if the satellite is equipped
with two antennas (like the SRTM instrumentation), collect sufficient data to
generate a digital elevation map.
2. Data Capture through Phogrammetry:
Other kinds of stereoscopic pairs can be employed using the digital image
correlation method, where two optical images are acquired with different
angles taken from the same pass of an airplane or an Earth Observation
Satellite (such as the HRS instrument of SPOT5 or the VNIR band of ASTER).
12. Data Capture
3. Data Capture through Land Surveying:
Older methods of generating DEMs often involve interpolating digital contour
maps that may have been produced by direct survey of the land surface. This
method is still used in mountain areas, where inter-ferometry is not always
satisfactory.
Note that contour line data or any other sampled elevation datasets (by GPS
or ground survey) are not DEMs, but may be considered digital terrain models
(DSM). A DEM implies that elevation is available continuously at each location
in the study area.
13. Data Collection Methods
Methods for obtaining elevation data used to create DEMs
Lidar
Stereo photogrammetry from aerial surveys
Structure from motion/ Multi-view stereo applied to aerial photography
Block adjustment from optical satellite imagery
Interferometry from radar data
Real Time Kinematic GPS
Topographic maps
Theodolite or total station
Doppler radar
Surveying and mapping drones
14. Quality of DEM
The quality of a DEM is a measure of how accurate elevation is at each pixel
(absolute accuracy) and how accurately is the morphology presented (relative
accuracy). Several factors play an important role for quality of DEM-derived
products:
• terrain roughness;
• sampling density (elevation data collection method);
• grid resolution or pixel size;
• Interpolation algorithm;
• vertical resolution;
• terrain analysis algorithm;
• Reference 3D products include quality masks that give information on the
coastline, lake, snow, clouds, correlation etc.
15. A DEM created from the same source data at 3 different post spacings (30 meters, 10 meters, and 3 meters
16. Free Data Sources
1. Space Shuttle Radar Topography Mission (SRTM)
This 1-arc second global digital elevation model has a spatial resolution of about 30 meters covering most of the world
with absolute vertical height accuracy of less than 16m. SRTM DEM data is being housed on the USGS Earth
Explorer server.
2. ASTER Global Digital Elevation Model
A joint operation between NASA and Japan was the birth of Advanced Spaceborne Thermal Emission and Reflection
Radiometer (ASTER). ASTER GDEM boasted a global resolution of 90 meters with a resolution of 30 meters in the
United States. You can download the ASTER DEM data for free from the “USGS Earth Explorer”.
3. JAXA’s Global ALOS 3D World
The ALOS World 3d is a 30-meter spatial resolution digital surface model (DSM) constructed by the Japan Aerospace
Exploration Agency’s (JAXA). It is the most precise global-scale elevation data at this time using the Advanced Land
Observing Satellite “DAICHI” (ALOS). The DSM was generated using stereo mapping (PRISM) for worldwide
topographic data with its optical stereoscopic observation. In order to obtain this highly accurate DSM, you’ll have to
register online through the “JAXA Global ALOS portal” to download it.
4. Indian Portal Bhuvan
CARTOSAT 1 and 2 derived stereo DEM, available for entire India freely. For specification and other details go
through Bhuvan website at http://bhuvan.nrsc.gov.in/data/download/index.php
17. Application of DEM
Common uses of DEMs include:
Extracting terrain parameters for geomorphology
Modeling water flow for hydrology or mass movement (for example
avalanches and landslides)
Modeling soils wetness with Cartographic Depth to Water Indexes (DTW-
index)
Creation of relief maps
Rendering of 3D visualizations.
3D flight planning and TERCOM
Creation of physical models (including raised relief maps)
Rectification of aerial photography or satellite imagery
Reduction (terrain correction) of gravity measurements (gravimetry,
physical geodesy)
18. Application of DEM
Common uses of DEMs include:
Terrain analysis in geomorphology and physical geography
Geographic Information Systems(GIS)
Engineering and infrastructure design
Satellite navigation(for example GPS and GLONASS)
Line-of-sight analysis
Base mapping
Flight simulation
Precision farming and forestry
Surface analysis
Intelligent transportation systems(ITS)
Auto safety / Advanced Driver Assistance Systems(ADAS)
Archaeology
20. • WorldDEM: Source of DEM
Video References:
• Digital Globe: Source of DEM (Must Watch!)
• Terrain Modelling using DEM & DTM
• Triangular Irregular Network (TIN)