Wikipedia

Digital elevation model

Adigital elevation model(DEM) ordigital surface model(DSM) is a3D computer graphicsrepresentation ofelevationdata to representterrainor overlaying objects, commonly of aplanet,moon,orasteroid.A "global DEM" refers to adiscrete global grid.DEMs are used often ingeographic information systems(GIS), and are the most common basis for digitally producedrelief maps. Adigital terrain model(DTM) represents specifically the ground surface while DEM and DSM may represent tree topcanopyorbuildingroofs.

3D renderingof a DEM ofTithonium ChasmaonMars

While a DSM may be useful forlandscape modeling,city modelingand visualization applications, a DTM is often required for flood or drainage modeling,land-use studies,[1]geological applications, and other applications,[2]and inplanetary science.

Terminology

edit
Surfaces represented by a Digital Surface Model include buildings and other objects. Digital Terrain Models represent the bare ground.

There is no universal usage of the termsdigital elevation model(DEM),digital terrain model(DTM) anddigital surface model(DSM) in scientific literature. In most cases the termdigital surface modelrepresents the earth's surface and includes all objects on it. In contrast to a DSM, thedigital 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 rectangulargridand a DTM as a three-dimensional model (TIN).[10] Most of the data providers (USGS,ERSDAC,CGIAR,Spot Image) use the term DEM as a generic term for DSMs and DTMs. Some datasets such asSRTMor theASTER GDEMare originally DSMs, although in forested areas, SRTM reaches into the tree canopy giving readings somewhere between a DSM and a DTM). DTMs are created from high resolution DSM datasets using complex algorithms to filter out buildings and other objects, a process known as "bare-earth extraction".[11][12] In the following, the term DEM is used as a generic term for DSMs and DTMs.

Types

edit
Heightmap of Earth's surface (including water and ice), rendered as anequirectangular projectionwith elevations indicated as normalized 8-bit grayscale, where lighter values indicate higher elevation

A DEM can be represented as araster(a grid of squares, also known as aheightmapwhen representing elevation) or as a vector-basedtriangular irregular network(TIN).[13]The TIN DEM dataset is also referred to as a primary (measured) DEM, whereas the Raster DEM is referred to as a secondary (computed) DEM.[14]The DEM could be acquired through techniques such asphotogrammetry,lidar,IfSARorInSAR,land surveying,etc. (Li et al. 2005).

DEMs are commonly built using data collected using remote sensing techniques, but they may also be built from land surveying.

Rendering

edit
Relief map of Spain's Sierra Nevada, showing use of both shading and false color as visualization tools to indicate elevation

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 contouredtopographic map,or could use shading andfalse colorassignment (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

edit

Mappers may prepare digital elevation models in a number of ways, but they frequently useremote sensingrather than directsurveydata.

Older methods of generating DEMs often involveinterpolatingdigital contour maps that may have been produced by direct survey of the land surface. This method is still used inmountainareas, whereinterferometryis not always satisfactory. Note thatcontour linedata 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

edit

One powerful technique for generating digital elevation models isinterferometric synthetic aperture radarwhere two passes of a radar satellite (such asRADARSAT-1orTerraSAR-XorCosmo SkyMed), or a single pass if the satellite is equipped with two antennas (like theSRTMinstrumentation), collect sufficient data to generate a digital elevation map tens of kilometers on a side with a resolution of around ten meters.[18]Other kinds ofstereoscopicpairs can be employed using thedigital image correlationmethod, where two optical images are acquired with different angles taken from the same pass of an airplane or anEarth Observation Satellite(such as the HRS instrument ofSPOT5or theVNIRband ofASTER).[19]

TheSPOT 1 satellite(1986) provided the first usable elevation data for a sizeable portion of the planet's landmass, using two-pass stereoscopic correlation. Later, further data were provided by theEuropean Remote-Sensing Satellite(ERS, 1991) using the same method, theShuttle Radar Topography Mission(SRTM, 2000) using single-pass SAR and theAdvanced Spaceborne Thermal Emission and Reflection Radiometer(ASTER, 2000) instrumentation on theTerra satelliteusing double-pass stereo pairs.[19]

The HRS instrument on SPOT 5 has acquired over 100 million square kilometers of stereo pairs.

Planetary mapping

edit
MOLA digital elevation model showing the two hemispheres of Mars. This image appeared on the cover ofSciencemagazine in May 1999.

A tool of increasing value inplanetary sciencehas been use of orbital altimetry used to make digital elevation map of planets. A primary tool for this islaser altimetrybut radar altimetry is also used.[20]Planetary digital elevation maps made using laser altimetry include theMars Orbiter Laser Altimeter(MOLA) mapping of Mars,[21]theLunar Orbital Laser Altimeter(LOLA)[22]and Lunar Altimeter (LALT) mapping of the Moon, and the Mercury Laser Altimeter (MLA) mapping of Mercury.[23]In planetary mapping, each planetary body has a unique reference surface.[24]

Methods for obtaining elevation data used to create DEMs

edit
Gatewing X100unmanned aerial vehicle

Accuracy

edit

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 orpixelsize;
  • interpolationalgorithm;
  • vertical resolution;
  • terrain analysis algorithm;
  • Reference 3D products include quality masks that give information on the coastline, lake, snow, clouds, correlation etc.

Uses

edit
Digital Elevation Model - Red Rocks Amphitheater, Colorado obtained using a UAV
Bezmiechowa airfield 3D Digital Surface Model obtained usingPteryx UAVflying 200 m above hilltop
Digital Surface Model ofmotorwayinterchangeconstruction site.Note that tunnels are closed.
Example DEM flown with the Gatewing X100 in Assenede
Digital Terrain Model Generator + Textures(Maps) + Vectors

Common uses of DEMs include:

Sources

edit

Global

edit

Released at the beginning of 2022,FABDEMoffers 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 thedeveloper's websiteat a cost commercially.

An alternative free global DEM is calledGTOPO30(30arcsecondresolution,c. 1kmalong the equator) is available, but its quality is variable and in some areas it is very poor. A much higher quality DEM from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument of theTerra satelliteis also freely available for 99% of the globe, and represents elevation at 30meterresolution. A similarly high resolution was previously only available for theUnited States territoryunder the Shuttle Radar Topography Mission (SRTM) data, while most of the rest of the planet was only covered in a 3 arc-second resolution (around 90 meters along the equator). SRTM does not cover the polar regions and has mountain and desert no data (void) areas. SRTM data, being derived from radar, represents the elevation of the first-reflected surface—quite often tree tops. So, the data are not necessarily representative of the ground surface, but the top of whatever is first encountered by the radar.

Submarine elevation (known asbathymetry) data is generated using ship-mounteddepth soundings.When land topography and bathymetry is combined, a trulyglobal relief modelis obtained. The SRTM30Plus dataset (used inNASA World Wind) attempts to combine GTOPO30, SRTM and bathymetric data to produce a truly global elevation model.[30]The Earth2014 global topography and relief model[31]provides layered topography grids at 1 arc-minute resolution. Other than SRTM30plus, Earth2014 provides information on ice-sheet heights and bedrock (that is, topography below the ice) over Antarctica and Greenland. Another global model is Global Multi-resolution Terrain Elevation Data 2010 (GMTED2010) with 7.5 arc second resolution. It is based on SRTM data and combines other data outside SRTM coverage. A novel global DEM of postings lower than 12 m and a height accuracy of less than 2 m is expected from theTanDEM-Xsatellite mission which started in July 2010.

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.[32]The radar satelliteRADARSAT-2has been used byMacDonald, Dettwiler and Associates Ltd.to provide DEMs for commercial and military customers.[33]

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

edit

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 ofnational lidar datasetprograms.

Free DEMs are also available forMars:the MEGDR, or Mission Experiment Gridded Data Record, from theMars Global Surveyor's Mars Orbiter Laser Altimeter (MOLA) instrument; and NASA's Mars Digital Terrain Model (DTM).[37]

Websites

edit

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]

STL 3D modelof theMoonwith 10× elevation exaggeration rendered with data from theLunar Orbiter Laser Altimeterof theLunar Reconnaissance Orbiter

See also

edit

DEM file formats

edit

References

edit
  1. ^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.
  2. ^"Appendix A – Glossary and Acronyms"(PDF).Severn Tidal Tributaries Catchment Flood Management Plan – Scoping Stage.UK:Environment Agency.Archived fromthe original(PDF)on 2007-07-10.
  3. ^"Intermap Digital Surface Model: accurate, seamless, wide-area surface models".Archived fromthe originalon 2011-09-28.
  4. ^Li, Z., Zhu, Q. and Gold, C. (2005),Digital terrain modeling: principles and methodology,CRC Press, Boca Raton, FL.
  5. ^Hirt, C. (2014)."Digital Terrain Models"(PDF).Encyclopedia of Geodesy.pp. 1–6.doi:10.1007/978-3-319-02370-0_31-1.ISBN978-3-319-01868-3.RetrievedOctober 14,2024.
  6. ^Peckham, Robert Joseph; Jordan, Gyozo (Eds.)(2007): Development and Applications in a Policy Support Environment Series: Lecture Notes in Geoinformation and Cartography. Heidelberg.
  7. ^Podobnikar, Tomaz (2008)."Methods for visual quality assessment of a digital terrain model".S.A.P.I.EN.S.1(2).
  8. ^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.
  9. ^"DIN Standard 18709-1".Archived fromthe originalon 2011-01-11.
  10. ^"Landslide Glossary USGS".Archived fromthe originalon 2011-05-16.
  11. ^Li, Z., Zhu, Q. and Gold, C. (2005),Digital terrain modeling: principles and methodology,CRC Press, Boca Raton, FL.
  12. ^"Understanding Digital Surface Models, Digital Terrain Models and Digital Elevation Models: A Comprehensive Guide to Digital Models of the Earth's Surface".FlyGuys.Retrieved7 September2023.
  13. ^DeMers, Michael (2002).GIS Modeling in Raster.Wiley.ISBN978-0-471-31965-8.
  14. ^RONALD TOPPE (1987):Terrain models — A tool for natural hazard MappingArchived2020-07-29 at theWayback Machine.In: Avalanche Formation, Movement and Effects (Proceedings of the Davos Symposium, September 1986). IAHS Publ. no. 162,1987
  15. ^Making 3D Terrain Maps,Shaded Relief.Retrieved 11 March 2019.
  16. ^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.
  17. ^Robert Simmon. "Elegant Figures What Not To Do: Vertical Exaggeration,"NASA Earth Observatory,November 5, 2010. Retrieved 11 March 2019.
  18. ^"WorldDEM(TM): Airbus Defence and Space".intelligence-airbusds.Archived fromthe originalon 2018-06-04.Retrieved2018-01-05.
  19. ^abNikolakopoulos, K. G.; Kamaratakis, E. K; Chrysoulakis, N. (10 November 2006)."SRTM vs ASTER elevation products. Comparison for two regions in Crete, Greece"(PDF).International Journal of Remote Sensing.27(21): 4819–4838.Bibcode:2006IJRS...27.4819N.doi:10.1080/01431160600835853.ISSN0143-1161.S2CID1939968.Archived fromthe original(PDF)on July 21, 2011.RetrievedJune 22,2010.
  20. ^Hargitai, Henrik; Willner, Konrad; Buchroithner, Manfred (2019), Hargitai, Henrik (ed.), "Methods in Planetary Topographic Mapping: A Review",Planetary Cartography and GIS,Lecture Notes in Geoinformation and Cartography, Springer International Publishing, pp. 147–174,doi:10.1007/978-3-319-62849-3_6,ISBN978-3-319-62848-6,S2CID133855780
  21. ^Bruce Banerdt,Orbital Laser Altimeter,The Martian Chronicle, Volume 1,No. 3, NASA. Retrieved 11 March 2019.
  22. ^NASA,LOLA.Retrieved 11 March 2019.
  23. ^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.
  24. ^Hargitai, Henrik; Willner, Konrad; Hare, Trent (2019), Hargitai, Henrik (ed.), "Fundamental Frameworks in Planetary Mapping: A Review",Planetary Cartography and GIS,Lecture Notes in Geoinformation and Cartography, Springer International Publishing, pp. 75–101,doi:10.1007/978-3-319-62849-3_4,ISBN978-3-319-62848-6,S2CID133867607
  25. ^abCampbell, D. M. H.; White, B.; Arp, P. A. (2013-11-01)."Modeling and mapping soil resistance to penetration and rutting using LiDAR-derived digital elevation data".Journal of Soil and Water Conservation.68(6): 460–473.doi:10.2489/jswc.68.6.460.ISSN0022-4561.
  26. ^James, M. R.; Robson, S. (2012)."Straightforward reconstruction of 3D surfaces and topography with a camera: Accuracy and geoscience application"(PDF).Journal of Geophysical Research: Earth Surface.117(F3): n/a.Bibcode:2012JGRF..117.3017J.doi:10.1029/2011JF002289.
  27. ^Szypuła, Bartłomiej (1 January 2019)."Quality assessment of DEM derived from topographic maps for geomorphometric purposes".Open Geosciences.11(1): 843–865.Bibcode:2019OGeo...11...66S.doi:10.1515/geo-2019-0066.hdl:20.500.12128/11742.ISSN2391-5447.S2CID208868204.
  28. ^Adams, Aaron (2019).A Comparative Usability Assessment of Augmented Reality 3-D Printed Terrain Models and 2-D Topographic Maps.NMSU.Retrieved11 March2022– via ProQuest.{{cite book}}:CS1 maint: location missing publisher (link)
  29. ^"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".
  30. ^"Martin Gamache's paper on free sources of global data"(PDF).
  31. ^Hirt, C.; Rexer, M. (2015)."Earth2014: 1 arc-min shape, topography, bedrock and ice-sheet models - available as gridded data and degree-10,800 spherical harmonics"(PDF).International Journal of Applied Earth Observation and Geoinformation.39:103–112.Bibcode:2015IJAEO..39..103H.doi:10.1016/j.jag.2015.03.001.hdl:20.500.11937/25468.RetrievedFebruary 20,2016.
  32. ^"GEO Elevation Services: Airbus Defence and Space".astrium-geo.Archived fromthe originalon 2014-06-26.Retrieved2012-01-11.
  33. ^"International - Geospatial".gs.mdacorporation.Archived fromthe originalon 2016-03-04.Retrieved2012-02-02.
  34. ^"TerraSAR-X: Airbus Defence and Space".astrium-geo.Archived fromthe originalon 2014-08-12.Retrieved2012-01-11.
  35. ^"ALOS World 3D - 30m".eorc.jaxa.jp.Archived fromthe originalon 2020-05-04.Retrieved2017-09-09.
  36. ^"ALOS World 3D".aw3d.jp.
  37. ^"A basic guide for using Digital Elevation Models with Terragen".Archived fromthe originalon 2007-05-19.
  38. ^"OpenTopography".opentopography.org.
  39. ^"About OpenTopography".
  40. ^"San Diego Supercomputer Center".sdsc.edu.Retrieved2018-08-16.
  41. ^"Home | UNAVCO".unavco.org.Retrieved2018-08-16.
  42. ^OpenDemSearcher

Further reading

edit
edit
Data products
Retrieved from "https://en.wikipedia.org/w/index.php?title=Digital_elevation_model&oldid=1251068948"