Digital elevation model
A digital elevation model (DEM) or digital surface model (DSM) is a 3D computer graphics representation of elevation data to represent terrain or overlaying objects, commonly of a planet, moon, or asteroid. A "global DEM" refers to a discrete global grid. DEMs are used often in geographic information systems (GIS), and are the most common basis for digitally produced relief maps. A digital terrain model (DTM) represents specifically the ground surface while DEM and DSM may represent tree top canopy or building roofs.
While a DSM may be useful for landscape modeling, city modeling and visualization applications, a DTM is often required for flood or drainage modeling, land-use studies,[1] geological applications, and other applications,[2] and in planetary science.
Terminology
There is no universal usage of the terms digital elevation model (DEM), digital terrain model (DTM) and digital surface model (DSM) in scientific literature. In most cases the term digital surface model represents the earth's surface and includes all objects on it. In contrast to a DSM, the digital terrain model (DTM) represents the bare ground surface without any objects like plants and buildings (see the figure on the right).[3][4]
DEM is often used as a generic term for DSMs and DTMs,[5] only representing height information without any further definition about the surface.[6] Other definitions equalise the terms DEM and DTM,[7] equalise the terms DEM and DSM,[8] define the DEM as a subset of the DTM, which also represents other morphological elements,[9] or define a DEM as a rectangular grid and a DTM as a three-dimensional model (TIN).[10] Most of the data providers (
Types
A DEM can be represented as a
DEMs are commonly built using data collected using remote sensing techniques, but they may also be built from land surveying.
Rendering
The digital elevation model itself consists of a matrix of numbers, but the data from a DEM is often rendered in visual form to make it understandable to humans. This visualization may be in the form of a contoured topographic map, or could use shading and false color assignment (or "pseudo-color") to render elevations as colors (for example, using green for the lowest elevations, shading to red, with white for the highest elevation.).
Visualizations are sometimes also done as oblique views, reconstructing a synthetic visual image of the terrain as it would appear looking down at an angle. In these oblique visualizations, elevations are sometimes scaled using "vertical exaggeration" in order to make subtle elevation differences more noticeable.[15] Some scientists,[16] [17] however, object to vertical exaggeration as misleading the viewer about the true landscape.
Production
Mappers may prepare digital elevation models in a number of ways, but they frequently use remote sensing rather than direct survey data.
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 interferometry 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. A DEM implies that elevation is available continuously at each location in the study area.
Satellite mapping
One powerful technique for generating digital elevation models is
The
The HRS instrument on SPOT 5 has acquired over 100 million square kilometers of stereo pairs.
Planetary mapping
A tool of increasing value in
Methods for obtaining elevation data used to create DEMs
- Lidar[25]
- Radar
- aerial surveys
- Structure from motion / Multi-view stereo applied to aerial photography[26]
- Block adjustment from optical satellite imagery
- Interferometry from radar data
- GPS
- Topographic maps
- Theodolite or total station
- Doppler radar
- Focus variation
- Inertial surveys
- Surveying and mapping drones
- Range imaging
Accuracy
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). Quality assessment of DEM can be performed by comparison of DEMs from different sources.[27] 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.
Uses
Common uses of DEMs include:
- Extracting terrain parameters for geomorphology
- Modeling )
- Modeling soils wetness with Cartographic Depth to Water Indexes (DTW-index)[25]
- Creation of relief maps
- Rendering of 3D visualizations.
- 3D flight planning and TERCOM
- Creation of physical models (including raised relief maps and 3D printed terrain models)[28]
- Rectification of aerial photography or satellite imagery
- Reduction (terrain correction) of gravity measurements (gravimetry, physical geodesy)
- 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
- Train simulation
- Surface analysis
- Intelligent transportation systems(ITS)
- Auto safety / advanced driver-assistance systems(ADAS)
- Archaeology
Sources
Global
Released at the beginning of 2022, FABDEM offers a bare earth simulation of the Earth's surface at 30 arc-second resolution. Adapted from GLO-30, the data removes all forests and buildings. The data is free to download non-commercially and through the developer's website at a cost commercially.
An alternative free global DEM is called
Submarine elevation (known as
The most common grid (raster) spacing is between 50 and 500 meters. In gravimetry e.g., the primary grid may be 50 m, but is switched to 100 or 500 meters in distances of about 5 or 10 kilometers.
Since 2002, the HRS instrument on SPOT 5 has acquired over 100 million square kilometers of stereo pairs used to produce a DTED2 format DEM (with a 30-meter posting) DEM format DTED2 over 50 million km2.
In 2014, acquisitions from radar satellites TerraSAR-X and TanDEM-X will be available in the form of a uniform global coverage with a resolution of 12 meters.[34]
ALOS provides since 2016 a global 1-arc second DSM free of charge,[35] and a commercial 5 meter DSM/DTM.[36]
Local
Many national mapping agencies produce their own DEMs, often of a higher resolution and quality, but frequently these have to be purchased, and the cost is usually prohibitive to all except public authorities and large corporations. DEMs are often a product of national lidar dataset programs.
Free DEMs are also available for Mars: the MEGDR, or Mission Experiment Gridded Data Record, from the Mars Global Surveyor's Mars Orbiter Laser Altimeter (MOLA) instrument; and NASA's Mars Digital Terrain Model (DTM).[37]
Websites
OpenTopography[38] is a web based community resource for access to high-resolution, Earth science-oriented, topography data (lidar and DEM data), and processing tools running on commodity and high performance compute system along with educational resources.[39] OpenTopography is based at the San Diego Supercomputer Center[40] at the University of California San Diego and is operated in collaboration with colleagues in the School of Earth and Space Exploration at Arizona State University and UNAVCO.[41] Core operational support for OpenTopography comes from the National Science Foundation, Division of Earth Sciences.
The OpenDemSearcher is a Mapclient with a visualization of regions with free available middle and high resolution DEMs.[42]
See also
- Ground slope and aspect (ground spatial gradient)
- Digital outcrop model
- Global Relief Model
- Physical terrain model
- Terrain cartography
- Terrain rendering
DEM file formats
References
- ^ I. Balenovic, H. Marjanovic, D. Vuletic, etc. Quality assessment of high density digital surface model over different land cover classes. PERIODICUM BIOLOGORUM. VOL. 117, No 4, 459–470, 2015.
- ^ "Appendix A – Glossary and Acronyms" (PDF). Severn Tidal Tributaries Catchment Flood Management Plan – Scoping Stage. UK: Environment Agency. Archived from the original (PDF) on 2007-07-10.
- ^ "Intermap Digital Surface Model: accurate, seamless, wide-area surface models". Archived from the original on 2011-09-28.
- ^ Li, Z., Zhu, Q. and Gold, C. (2005), Digital terrain modeling: principles and methodology, CRC Press, Boca Raton, FL.
- ISBN 978-3-319-01868-3. Retrieved February 10, 2016.
- ^ Peckham, Robert Joseph; Jordan, Gyozo (Eds.)(2007): Development and Applications in a Policy Support Environment Series: Lecture Notes in Geoinformation and Cartography. Heidelberg.
- ^ Podobnikar, Tomaz (2008). "Methods for visual quality assessment of a digital terrain model". S.A.P.I.EN.S. 1 (2).
- ^ Adrian W. Graham, Nicholas C. Kirkman, Peter M. Paul (2007): Mobile radio network design in the VHF and UHF bands: a practical approach. West Sussex.
- ^ "DIN Standard 18709-1". Archived from the original on 2011-01-11.
- ^ "Landslide Glossary USGS". Archived from the original on 2011-05-16.
- ^ Li, Z., Zhu, Q. and Gold, C. (2005), Digital terrain modeling: principles and methodology, CRC Press, Boca Raton, FL.
- ^ "Understanding Digital Surface Models, Digital Terrain Models and Digital Elevation Models: A Comprehensive Guide to Digital Models of the Earth's Surface". FlyGuys. Retrieved 7 September 2023.
- ISBN 978-0-471-31965-8.
- ^ RONALD TOPPE (1987): Terrain models — A tool for natural hazard Mapping Archived 2020-07-29 at the Wayback Machine. In: Avalanche Formation, Movement and Effects (Proceedings of the Davos Symposium, September 1986). IAHS Publ. no. 162,1987
- ^ Making 3D Terrain Maps, Shaded Relief. Retrieved 11 March 2019.
- ^ David Morrison, ""Flat-Venus Society" organizes", EOS, Volume 73, Issue 9, American Geophysical Union, 3 March 1992, p. 99. https://doi.org/10.1029/91EO00076. Retrieved 11 March 2019.
- ^ Robert Simmon. "Elegant Figures What Not To Do: Vertical Exaggeration," NASA Earth Observatory, November 5, 2010. Retrieved 11 March 2019.
- ^ "WorldDEM(TM): Airbus Defence and Space". www.intelligence-airbusds.com. Archived from the original on 2018-06-04. Retrieved 2018-01-05.
- ^ S2CID 1939968. Archived from the original(PDF) on July 21, 2011. Retrieved June 22, 2010.
- S2CID 133855780
- ^ Bruce Banerdt, Orbital Laser Altimeter, The Martian Chronicle, Volume 1, No. 3, NASA. Retrieved 11 March 2019.
- ^ NASA, LOLA. Retrieved 11 March 2019.
- ^ John F. Cavanaugh, et al., "The Mercury Laser Altimeter Instrument for the MESSENGER Mission", Space Sci Rev, DOI 10.1007/s11214-007-9273-4, 24 August 2007. Retrieved 11 March 2019.
- S2CID 133867607
- ^ ISSN 0022-4561.
- .
- S2CID 208868204.
- ^ Adams, Aaron (2019). A Comparative Usability Assessment of Augmented Reality 3-D Printed Terrain Models and 2-D Topographic Maps. NMSU. Retrieved 11 March 2022 – via ProQuest.
{{cite book}}
: CS1 maint: location missing publisher (link) - ^ "I. Balenović, A. Seletković, R. Pernar, A. Jazbec. Estimation of the mean tree height of forest stands by photogrammetric measurement using digital aerial images of high spatial resolution. ANNALS OF FOREST RESEARCH. 58(1), P. 125-143, 2015".
- ^ "Martin Gamache's paper on free sources of global data" (PDF).
- . Retrieved February 20, 2016.
- ^ "GEO Elevation Services : Airbus Defence and Space". www.astrium-geo.com. Archived from the original on 2014-06-26. Retrieved 2012-01-11.
- ^ "International - Geospatial". gs.mdacorporation.com. Archived from the original on 2016-03-04. Retrieved 2012-02-02.
- ^ "TerraSAR-X : Airbus Defence and Space". www.astrium-geo.com. Archived from the original on 2014-08-12. Retrieved 2012-01-11.
- ^ "ALOS World 3D - 30m". www.eorc.jaxa.jp. Archived from the original on 2020-05-04. Retrieved 2017-09-09.
- ^ "ALOS World 3D". www.aw3d.jp.
- ^ "A basic guide for using Digital Elevation Models with Terragen". Archived from the original on 2007-05-19.
- ^ "OpenTopography". www.opentopography.org.
- ^ "About OpenTopography".
- ^ "San Diego Supercomputer Center". www.sdsc.edu. Retrieved 2018-08-16.
- ^ "Home | UNAVCO". www.unavco.org. Retrieved 2018-08-16.
- ^ OpenDemSearcher
Further reading
- Wilson, J.P.; Gallant, J.C. (2000). "Chapter 1" (PDF). In Wilson, J.P.; Gallant, J.C. (eds.). Terrain Analysis: Principles and Applications. New York: Wiley. pp. 1–27. ISBN 978-0-471-32188-0. Retrieved 2007-02-16.
- Hirt, C.; Filmer, M.S.; Featherstone, W.E. (2010). "Comparison and validation of recent freely-available ASTER-GDEM ver1, SRTM ver4.1 and GEODATA DEM-9S ver3 digital elevation models over Australia". Australian Journal of Earth Sciences. 57 (3): 337–347. S2CID 140651372. Retrieved May 5, 2012.
- Rexer, M.; Hirt, C. (2014). "Comparison of free high-resolution digital elevation data sets (ASTER GDEM2, SRTM v2.1/v4.1) and validation against accurate heights from the Australian National Gravity Database" (PDF). Australian Journal of Earth Sciences. 61 (2): 213–226. S2CID 3783826. Archived from the original(PDF) on June 7, 2016. Retrieved April 24, 2014.
External links
- DEM Quality Comparison
- Terrainmap.com
- Maps-for-free.com
- Geo-Spatial Data Acquisition Archived 2013-08-22 at the Wayback Machine
- Elevation Mapper, Create geo-referenced elevation maps
- Data products
- Satellite Geodesy by Scripps Institution of Oceanography
- Shuttle Radar Topography Mission by NASA/JPL
- Global 30 Arc-Second Elevation (GTOPO30) by the U.S. Geological Survey
- Global Multi-resolution Terrain Elevation Data 2010 (GMTED2010) by the U.S. Geological Survey
- Earth2014 by Technische Universität München
- Sonny's LiDAR Digital Terrain Models of European countries