Editing Digital elevation model

{{Short description|3D computer-generated imagery and measurements of terrain}}
[[File:Mtm-05277e 3d.png|thumb|upright=1.3|[[3D computer graphics|3D rendering]] of a DTM of [[Tithonium Chasma]] on [[Mars]]]]

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]], [[Natural satellite|moon]], or [[asteroid]]. A "global DEM" refers to a  [[discrete global grid]]. DEMs are used often in [[geographic information system]]s (GIS), and are the most common basis for digitally produced [[Relief mapping (computer graphics)|relief map]]s. 
A '''digital terrain model''' ('''DTM''') represents specifically the ground surface while DEM and DSM may represent tree top [[Canopy (biology)|canopy]] or [[building]] roofs.

While a DSM may be useful for [[Landscape planning|landscape modeling]], [[Urban planning|city modeling]] and visualization applications, a DTM is often required for flood or drainage modeling, [[Land-use planning|land-use studies]],<ref>[http://www.racurs.ru/www_download/articles/Balenovic.pdf 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.]</ref> geological applications, and other applications,<ref>{{cite book |chapter=Appendix A – Glossary and Acronyms |title=Severn Tidal Tributaries Catchment Flood Management Plan – Scoping Stage |chapter-url=http://www.environment-agency.gov.uk/commondata/acrobat/app_a_1243533.pdf |publisher=[[Environment Agency]] |location=UK |url-status=dead |archive-url=https://web.archive.org/web/20070710054700/http://www.environment-agency.gov.uk/commondata/acrobat/app_a_1243533.pdf |archive-date=2007-07-10 }}</ref> and in [[planetary science]].

== Terminology ==
[[File:DTM DSM.svg|thumb|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 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).<ref>{{cite web|title=Intermap Digital Surface Model: accurate, seamless, wide-area surface models |url=http://www.intermap.com/en-us/nextmap/digitalsurfacemodel.aspx |url-status=dead |archive-url=https://web.archive.org/web/20110928170504/http://www.intermap.com/en-us/nextmap/digitalsurfacemodel.aspx |archive-date=2011-09-28 }}</ref><ref>Li, Z., Zhu, Q. and Gold, C. (2005), ''Digital terrain modeling: principles and methodology,'' CRC Press, Boca Raton, FL.</ref>

DEM is often used as a generic term for DSMs and DTMs,<ref name=Hirt2015>{{cite book|last1=Hirt|first1=C.|title=Encyclopedia of Geodesy |chapter=Digital Terrain Models |pages=1–6|isbn=  978-3-319-01868-3|chapter-url= https://mediatum.ub.tum.de/doc/1375750/54500.pdf|access-date=October 14, 2024|doi=10.1007/978-3-319-02370-0_31-1|year=2014}}</ref> only representing height information without any further definition about the surface.<ref>Peckham, Robert Joseph; Jordan, Gyozo (Eds.)(2007):  Development and Applications in a Policy Support Environment Series: Lecture Notes in Geoinformation and Cartography.  Heidelberg.</ref> 
Other definitions equalise the terms DEM and DTM,<ref>{{cite journal |last=Podobnikar |first=Tomaz |year=2008 |title=Methods for visual quality assessment of a digital terrain model |journal=S.A.P.I.EN.S |volume=1 |issue=2 |url=http://sapiens.revues.org/index738.html }}</ref> equalise the terms DEM and DSM,<ref>Adrian W. Graham, Nicholas C. Kirkman, Peter M. Paul (2007): [https://books.google.com/books?id=j5ePLBWYAOgC Mobile radio network design in the VHF and UHF bands: a practical approach]. West Sussex.</ref> 
define the DEM as a subset of the DTM, which also represents other morphological elements,<ref>{{cite web|url=http://www.din.de/cmd?level=tpl-home&languageid=en|title=DIN Standard 18709-1|url-status=dead|archive-url=https://web.archive.org/web/20110111174038/http://www.din.de/cmd?level=tpl-home&languageid=en|archive-date=2011-01-11}}</ref> or define a DEM as a rectangular [[Grid (spatial index)|grid]] and a DTM as a three-dimensional model ([[triangulated irregular network|TIN]]).<ref>{{cite web|url=http://landslides.usgs.gov/learning/glossary.php#d |title=Landslide Glossary USGS |url-status=dead |archive-url=https://web.archive.org/web/20110516134523/http://landslides.usgs.gov/learning/glossary.php |archive-date=2011-05-16 }}</ref> 
Most of the data providers ([[USGS]], [[Advanced Spaceborne Thermal Emission and Reflection Radiometer|ERSDAC]], [[CGIAR]], [[Spot Image]]) use the term DEM as a generic term for DSMs and DTMs. Some datasets such as [[SRTM]] or the [[Advanced Spaceborne Thermal Emission and Reflection Radiometer|ASTER GDEM]] are 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".<ref>Li, Z., Zhu, Q. and Gold, C. (2005), ''Digital terrain modeling: principles and methodology,'' CRC Press, Boca Raton, FL.</ref><ref>{{cite web |title=Understanding Digital Surface Models, Digital Terrain Models and Digital Elevation Models: A Comprehensive Guide to Digital Models of the Earth's Surface |url=https://flyguys.com/understanding-dsm-dtm-dem/ |website=FlyGuys |access-date=7 September 2023}}</ref>
In the following, the term DEM is used as a generic term for DSMs and DTMs.

==Types==
[[Image:srtm ramp2.world.21600x10800.jpg|thumb|Heightmap of Earth's surface (including water and ice), rendered as an [[equirectangular projection]] with elevations indicated as normalized 8-bit grayscale, where lighter values indicate higher elevation]]
A DEM can be represented as a [[Raster graphics|raster]] (a grid of squares, also known as a [[heightmap]] when representing elevation) or as a vector-based [[triangular irregular network]] (TIN).<ref>{{cite book |last1=DeMers |first1=Michael |title=GIS Modeling in Raster |date=2002 |publisher=Wiley |isbn=978-0-471-31965-8}}</ref> 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.<ref>RONALD TOPPE (1987): [http://hydrologie.org/redbooks/a162/iahs_162_0629.pdf Terrain models — A tool for natural hazard Mapping] {{Webarchive|url=https://web.archive.org/web/20200729221913/http://hydrologie.org/redbooks/a162/iahs_162_0629.pdf |date=2020-07-29 }}. In: Avalanche Formation, Movement and Effects (Proceedings of the Davos Symposium, September 1986). IAHS Publ. no. 162,1987</ref>  The DEM could be acquired through techniques such as [[photogrammetry]], [[lidar]], [[IFSAR|IfSAR]] or [[InSAR]], [[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===
[[File:Maps-for-free Sierra Nevada.png|thumb|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 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.<ref>[http://shadedrelief.com/3D_Terrain_Maps/3dterrainmapsver.html Making 3D Terrain Maps], ''Shaded Relief''. Retrieved 11 March 2019.</ref> Some scientists,<ref>David Morrison, "[https://doi.org/10.1029/91EO00076 "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.</ref>
<ref name="Simon2010">Robert Simmon. "[https://earthobservatory.nasa.gov/blogs/elegantfigures/2010/11/05/what-not-to-do-vertical-exaggeration/ Elegant Figures What Not To Do: Vertical Exaggeration]," ''NASA Earth Observatory,'' November 5, 2010. Retrieved 11 March 2019.</ref> 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 [[Surveying|survey]] data.

Older methods of generating DEMs often involve [[interpolation|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 [[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 [[Shuttle Radar Topography Mission|SRTM]] instrumentation), collect sufficient data to generate a digital elevation map tens of kilometers on a side with a resolution of around ten meters.<ref>{{cite web|url=http://www.intelligence-airbusds.com/worlddem/|title=WorldDEM(TM): Airbus Defence and Space|website=www.intelligence-airbusds.com|access-date=2018-01-05|archive-date=2018-06-04|archive-url=https://web.archive.org/web/20180604103046/http://www.intelligence-airbusds.com/worlddem/|url-status=dead}}</ref> 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 [[SPOT (satellites)|SPOT5]] or the [[VNIR]] band of [[Advanced Spaceborne Thermal Emission and Reflection Radiometer|ASTER]]).<ref name=Nikolakopoulous>{{cite journal|last1=Nikolakopoulos |first1=K. G. |last2=Kamaratakis |first2=E. K |last3=Chrysoulakis |first3=N. |date=10 November 2006 |title=SRTM vs ASTER elevation products. Comparison for two regions in Crete, Greece |journal=International Journal of Remote Sensing |volume=27 |issue=21 |pages=4819–4838 |issn=0143-1161 |url=http://www.iacm.forth.gr/_docs/pubs/4/Nikolakopoulos_et_al_2006.pdf |access-date=June 22, 2010 |doi=10.1080/01431160600835853 |bibcode=2006IJRS...27.4819N |s2cid=1939968 |url-status=dead |archive-url=https://web.archive.org/web/20110721081314/http://www.iacm.forth.gr/_docs/pubs/4/Nikolakopoulos_et_al_2006.pdf |archive-date=July 21, 2011 }}</ref>

The [[SPOT (satellites)|SPOT 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 the [[European Remote-Sensing Satellite]] (ERS, 1991) using the same method, the [[Shuttle Radar Topography Mission]] (SRTM, 2000) using single-pass SAR and the [[Advanced Spaceborne Thermal Emission and Reflection Radiometer]] (ASTER, 2000) instrumentation on the [[Terra satellite]] using double-pass stereo pairs.<ref name=Nikolakopoulous/>

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

===Planetary mapping===
[[image:PIA02040 Martian hemispheres by MOLA.jpg|upright=1.2|thumb|MOLA digital elevation model showing the two hemispheres of Mars. This image appeared on the cover of ''Science'' magazine in May 1999.]]
A tool of increasing value in [[planetary science]] has been use of orbital altimetry used to make digital elevation map of planets.  A primary tool for this is [[Lidar|laser altimetry]] but radar altimetry is also used.<ref>{{Citation|last1=Hargitai|first1=Henrik|title=Methods in Planetary Topographic Mapping: A Review|date=2019|work=Planetary Cartography and GIS|pages=147–174|editor-last=Hargitai|editor-first=Henrik|publisher=Springer International Publishing|language=en|doi=10.1007/978-3-319-62849-3_6|isbn=978-3-319-62848-6|last2=Willner|first2=Konrad|last3=Buchroithner|first3=Manfred|series=Lecture Notes in Geoinformation and Cartography |s2cid=133855780}}</ref> Planetary digital elevation maps made using laser altimetry include the [[Mars Orbiter Laser Altimeter]] (MOLA) mapping of Mars,<ref name=" Banerdt">Bruce Banerdt, [https://mars.nasa.gov/MPF/martianchronicle/martianchron3/marschro35.html Orbital Laser Altimeter], ''The Martian Chronicle, Volume 1'', No. 3, NASA.  Retrieved 11 March 2019.</ref> the [[Lunar Orbital Laser Altimeter]] (LOLA)<ref>NASA, [https://lola.gsfc.nasa.gov LOLA].  Retrieved 11 March 2019.</ref> and Lunar Altimeter (LALT) mapping of the Moon, and the Mercury Laser Altimeter (MLA) mapping of Mercury.<ref>John F. Cavanaugh, ''et al.,'' "[http://www-geodyn.mit.edu/cavanaugh.mla.ssr07.pdf 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.</ref> In planetary mapping, each planetary body has a unique reference surface.<ref>{{Citation|last1=Hargitai|first1=Henrik|title=Fundamental Frameworks in Planetary Mapping: A Review|date=2019|work=Planetary Cartography and GIS|pages=75–101|editor-last=Hargitai|editor-first=Henrik|publisher=Springer International Publishing|language=en|doi=10.1007/978-3-319-62849-3_4|isbn=978-3-319-62848-6|last2=Willner|first2=Konrad|last3=Hare|first3=Trent|series=Lecture Notes in Geoinformation and Cartography |s2cid=133867607}}</ref> [[New Horizons|New Horizons']] Long Range Reconnaissance Imager used stereo photogrammetry to produce partial surface elevation maps of [[Pluto]] and [[486958 Arrokoth]].<ref>{{cite web |title=Astropedia - Pluto New Horizons LORRI - MVIC Global DEM 300m |url=https://astrogeology.usgs.gov/search/map/pluto_new_horizons_lorri_mvic_global_dem_300m |website=astrogeology.usgs.gov}}</ref><ref>{{cite journal |last1=Schenk |first1=Paul |last2=Singer |first2=Kelsi |last3=Beyer |first3=Ross |last4=Beddingfield |first4=Chloe |last5=Robbins |first5=Stuart J. |last6=McKinnon |first6=William B. |last7=Lauer |first7=Tod R. |last8=Verbiscer |first8=Anne J. |last9=Keane |first9=James. T. |last10=Dhingra |first10=Rajani D. |last11=Moore |first11=Jeffrey |last12=Parker |first12=Joel W. |last13=Olkin |first13=Cathy |last14=Spencer |first14=John |last15=Weaver |first15=Hal |last16=Stern |first16=S. Alan |title=Origins of pits and troughs and degradation on a small primitive planetesimal in the Kuiper Belt: high-resolution topography of (486958) Arrokoth (aka 2014 MU69) from New Horizons |journal=Icarus |date=1 March 2021 |volume=356 |pages=113834 |doi=10.1016/j.icarus.2020.113834 |issn=0019-1035}}</ref>

===Methods for obtaining elevation data used to create DEMs===

[[File:GatewingX100.jpg|thumb|Gatewing X100 [[unmanned aerial vehicle]]]]

* [[Lidar]]<ref name="Campbell"/>
* [[Radar]]
* [[Stereo photogrammetry]] from [[aerial surveys]]
** [[Structure from motion]] / Multi-view stereo applied to aerial photography<ref>{{Cite journal | doi=10.1029/2011JF002289| title=Straightforward reconstruction of 3D surfaces and topography with a camera: Accuracy and geoscience application| journal=Journal of Geophysical Research: Earth Surface| volume=117| year=2012| last1=James| first1=M. R.| last2=Robson| first2=S.| issue=F3| pages=n/a| bibcode=2012JGRF..117.3017J| url=https://eprints.lancs.ac.uk/id/eprint/56018/1/James_and_Robson_2012_SfM_MVS.pdf| doi-access=free}}</ref>
* Block adjustment from optical satellite imagery
* Interferometry from radar data
* [[Real Time Kinematic]] [[GPS]]
* [[Topographic map]]s
* [[Theodolite]] or [[total station]]
* [[Doppler radar]]
* [[Focus variation]]
* Inertial surveys
* Surveying and mapping [[UAV|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.<ref>{{cite journal |last1=Szypuła |first1=Bartłomiej |title=Quality assessment of DEM derived from topographic maps for geomorphometric purposes |journal=Open Geosciences |date=1 January 2019 |volume=11 |issue=1 |pages=843–865 |doi=10.1515/geo-2019-0066 |bibcode=2019OGeo...11...66S |url=https://doi.org/10.1515/geo-2019-0066 |language=en |issn=2391-5447|hdl=20.500.12128/11742 |s2cid=208868204 |hdl-access=free }}</ref> 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==
[[File:Digital Elevation Model - Red Rocks Amphitheater, Colorado.jpg|thumb|Digital Elevation Model - Red Rocks Amphitheater, Colorado obtained using a UAV]]

[[File:Bezmiechowa DSM 3D 2010-05-29 Pteryx UAV.jpg|thumb|Bezmiechowa airfield 3D Digital Surface Model obtained using [[Pteryx UAV]] flying 200&nbsp;m above hilltop]]

[[File:DSM construction site.jpg|thumb|Digital Surface Model of [[motorway]] interchange [[construction site]]. Note that tunnels are closed.]]

[[File:DEM Assenede1.PNG|thumb|Example DEM flown with the Gatewing X100 in Assenede]]

[[Image:geabios3d.jpg|thumb|Digital Terrain Model Generator + Textures(Maps) + Vectors]]

Common uses of DEMs include:
* Extracting terrain parameters for [[geomorphology]]
* Modeling [[water flow]] for [[hydrology]] or mass movement (for example [[avalanche]]s and [[landslide]]s)
* Modeling soils wetness with Cartographic Depth to Water Indexes (DTW-index)<ref name="Campbell">{{Cite journal|last1=Campbell|first1=D. M. H.|last2=White|first2=B.|last3=Arp|first3=P. A.|date=2013-11-01|title=Modeling and mapping soil resistance to penetration and rutting using LiDAR-derived digital elevation data|journal=Journal of Soil and Water Conservation|language=en|volume=68|issue=6|pages=460–473|doi=10.2489/jswc.68.6.460|issn=0022-4561|doi-access=free}}</ref>
* Creation of relief maps
* Rendering of [[Visualization (computer graphics)|3D visualizations]].
* [[Flight planning|3D flight planning]] and [[TERCOM]]
* Creation of physical models (including [[raised relief map]]s and 3D printed terrain models)<ref>{{cite book |last1=Adams |first1=Aaron |title=A Comparative Usability Assessment of Augmented Reality 3-D Printed Terrain Models and 2-D Topographic Maps |date=2019 |location=NMSU |url=https://www.proquest.com/openview/2d2ba6f6f378dab8c217440f2d608e96/1?pq-origsite=gscholar&cbl=18750&diss=y |access-date=11 March 2022|via=ProQuest }}</ref>
* 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 system]]s (GIS)
* [[Engineering]] and [[infrastructure]] design
* [[Satellite navigation]] (for example [[Global Positioning System|GPS]] and [[GLONASS]])
* Line-of-sight analysis
* Base mapping
* [[Flight simulation]]
* [[Train simulation]]
* [[Precision farming]] and [[forestry]]<ref>{{cite web|url=http://afrjournal.org/index.php/afr/article/viewFile/300/416|title=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.}}</ref>
* [[Surface analysis]]
* [[Intelligent transportation systems]] (ITS)
* Auto safety / [[advanced driver-assistance systems]] (ADAS)
* [[Archaeology]]

==Sources==

=== Global ===
Released at the beginning of 2022, [https://www.fathom.global/academic-papers/a-30-m-global-map-of-elevation-with-forests-and-buildings-removed/ 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 [https://www.fathom.global/product/fabdem/ developer's website] at a cost commercially.

An alternative free global DEM is called [[GTOPO30]] (30 [[arcsecond]] [[Angular resolution|resolution]], c. 1&nbsp;[[km]]  along 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 the [[Terra satellite]] is also freely available for 99% of the globe, and represents elevation at 30 [[meter]] resolution. A similarly high resolution was previously only available for the [[United States territory]] under the Shuttle Radar Topography Mission (SRTM) data, while most of the rest of the planet was only covered in a 3&nbsp;arc-second resolution (around 90&nbsp;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&mdash;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 as [[bathymetry]]) data is generated using ship-mounted [[depth sounding]]s. When land topography and bathymetry is combined, a truly [[global relief model]]  is obtained.   The SRTM30Plus dataset (used in [[NASA World Wind]]) attempts to combine GTOPO30, SRTM and bathymetric data to produce a truly global elevation model.<ref>{{cite web|url=http://www.terrainmap.com/downloads/Gamache_final_web.pdf|title=Martin Gamache's paper on free sources of global data}}</ref>  The Earth2014 global topography and relief model<ref name=HirtRexer2015>{{cite journal|last1=Hirt|first1=C.|last2=Rexer|first2=M.|title=Earth2014: 1 arc-min shape, topography, bedrock and ice-sheet models - available as gridded data and degree-10,800 spherical harmonics|journal=International Journal of Applied Earth Observation and Geoinformation|volume=39|pages=103–112|url=http://ddfe.curtin.edu.au/models/Earth2014/Hirt_Rexer2015_Earth2014.pdf|access-date=February 20, 2016|doi=10.1016/j.jag.2015.03.001|year=2015|bibcode=2015IJAEO..39..103H|hdl=20.500.11937/25468|hdl-access=free}}</ref> 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&nbsp;m and a height accuracy of less than 2&nbsp;m is expected from the [[TanDEM-X]] satellite mission which started in July 2010.

The most common grid (raster) spacing is between 50 and 500&nbsp;meters. In gravimetry e.g., the primary grid may be 50&nbsp;m, but is switched to 100 or 500&nbsp;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 km<sup>2</sup>.<ref>{{cite web|url=http://www.astrium-geo.com/en/66-geo-elevation-and-dem|title=GEO Elevation Services : Airbus Defence and Space|website=www.astrium-geo.com|access-date=2012-01-11|archive-date=2014-06-26|archive-url=https://web.archive.org/web/20140626025812/http://www.astrium-geo.com/en/66-geo-elevation-and-dem|url-status=dead}}</ref> The radar satellite [[RADARSAT-2]] has been used by [[MacDonald, Dettwiler and Associates Ltd.]] to provide DEMs for commercial and military customers.<ref>{{cite web|url=http://gs.mdacorporation.com/Mapping/DigitalElevationModels.aspx|title=International - Geospatial|website=gs.mdacorporation.com|access-date=2012-02-02|archive-date=2016-03-04|archive-url=https://web.archive.org/web/20160304121452/http://gs.mdacorporation.com/Mapping/DigitalElevationModels.aspx|url-status=dead}}</ref>

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&nbsp;meters.<ref>{{cite web|url=http://www.astrium-geo.com/terrasar-x/|title=TerraSAR-X : Airbus Defence and Space|website=www.astrium-geo.com|access-date=2012-01-11|archive-date=2014-08-12|archive-url=https://web.archive.org/web/20140812160313/http://www.astrium-geo.com/terrasar-x/|url-status=dead}}</ref>

ALOS provides since 2016 a global 1-arc second DSM free of charge,<ref>{{cite web|url=http://www.eorc.jaxa.jp/ALOS/en/aw3d30/|title=ALOS World 3D - 30m|website=www.eorc.jaxa.jp|access-date=2017-09-09|archive-date=2020-05-04|archive-url=https://web.archive.org/web/20200504132807/https://www.eorc.jaxa.jp/ALOS/en/aw3d30/|url-status=dead}}</ref> and a commercial 5 meter DSM/DTM.<ref>{{cite web|url=http://www.aw3d.jp/en/products/|title=ALOS World 3D|website=www.aw3d.jp}}</ref>

=== 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).<ref>{{cite web|url=http://www2.cs.uh.edu/~somalley/DemTutorial/#DEM|title=A basic guide for using Digital Elevation Models with Terragen|url-status=dead|archive-url=https://web.archive.org/web/20070519135415/http://www2.cs.uh.edu/~somalley/DemTutorial/#DEM|archive-date=2007-05-19}}</ref>

=== Websites ===
OpenTopography<ref name="OpenTopography">{{cite web|url=http://www.opentopography.org/|title=OpenTopography|website=www.opentopography.org}}</ref> 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.<ref name="opentopography.org">{{cite web|url=http://www.opentopography.org/about/|title=About OpenTopography}}</ref> OpenTopography is based at the San Diego Supercomputer Center<ref>{{Cite web|url=http://www.sdsc.edu|title=San Diego Supercomputer Center|website=www.sdsc.edu|access-date=2018-08-16}}</ref> 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.<ref>{{Cite web|url=http://www.unavco.org|title=Home {{!}} UNAVCO|website=www.unavco.org|language=en-US|access-date=2018-08-16}}</ref> 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.<ref>[http://www.opendem.info/opendemsearcher.html  OpenDemSearcher]</ref>
[[File:Moon_elevation.stl|thumb|[[STL (file format)|STL 3D model]] of the [[Moon]] with 10× elevation exaggeration rendered with data from the [[Lunar Orbiter Laser Altimeter]] of the [[Lunar Reconnaissance Orbiter]] ]]

==See also==
* [[Ground slope]] and [[Aspect (geography)|aspect]] (ground [[spatial gradient]])
* [[Digital outcrop model]]
* [[Global Relief Model]]
* [[Physical terrain model]]
* [[Terrain cartography]]
* [[Terrain rendering]]

===DEM file formats===

* [[Bathymetric Attributed Grid]] (BAG)
* [[DTED]]
* DIMAP Sentinel 1 ESA data base
* [[Spatial Data Transfer Standard|SDTS]] DEM
* [[USGS DEM]]

==References==
{{Reflist}}

==Further reading==
*{{cite book |last=Wilson |first=J.P. |author2=Gallant, J.C. |editor=Wilson, J.P. |editor2=Gallant, J.C. |title=Terrain Analysis: Principles and Applications |access-date=2007-02-16 |year=2000 |publisher= Wiley|location= New York|isbn=978-0-471-32188-0 |pages=1–27 |chapter=Chapter 1 |chapter-url=http://media.wiley.com/product_data/excerpt/85/04713218/0471321885.pdf }}
* {{cite journal|last1=Hirt|first1=C.|last2=Filmer|first2=M.S. |last3=Featherstone|first3=W.E.|year=2010|title=Comparison and validation of recent freely-available ASTER-GDEM ver1, SRTM ver4.1 and GEODATA DEM-9S ver3 digital elevation models over Australia.|journal=Australian Journal of Earth Sciences|volume=57|issue=3|pages=337–347|url=http://espace.library.curtin.edu.au:80/R?func=dbin-jump-full&local_base=gen01-era02&object_id=137777|access-date=May 5, 2012|doi=10.1080/08120091003677553|bibcode=2010AuJES..57..337H|hdl=20.500.11937/43846|s2cid=140651372|hdl-access=free}}
* {{cite journal|last1=Rexer|first1=M.|last2=Hirt|first2=C.|year=2014|title=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.|journal=Australian Journal of Earth Sciences|volume=61|issue=2|pages=213–226|url=http://geodesy.curtin.edu.au:80/local/docs/Rexer_Hirt_2014_DEM_AJES_av.pdf|archive-url=https://web.archive.org/web/20160607102637/http://geodesy.curtin.edu.au/local/docs/Rexer_Hirt_2014_DEM_AJES_av.pdf|url-status=dead|archive-date=June 7, 2016|access-date=April 24, 2014|doi=10.1080/08120099.2014.884983|bibcode=2014AuJES..61..213R|hdl=20.500.11937/38264|s2cid=3783826|hdl-access=free}}

==External links==
* [https://www.loxcel.com/news-2023.html#2023-Mar-2 DEM Quality Comparison]
* [http://www.terrainmap.com/ Terrainmap.com]
* [http://www.maps-for-free.com Maps-for-free.com]
* [http://www.xmswiki.com/xms/GSDA:GSDA Geo-Spatial Data Acquisition] {{Webarchive|url=https://web.archive.org/web/20130822115452/http://www.xmswiki.com/xms/GSDA:GSDA |date=2013-08-22 }}
* [http://sites.google.com/site/elevationmapcreator Elevation Mapper, Create geo-referenced elevation maps]
;Data products
* [http://topex.ucsd.edu/ Satellite Geodesy] by [[Scripps Institution of Oceanography]]
* [http://www.jpl.nasa.gov/srtm/ Shuttle Radar Topography Mission] by NASA/JPL
* [https://web.archive.org/web/20170710005530/https://lta.cr.usgs.gov/gtopo30 Global 30 Arc-Second Elevation (GTOPO30)] by the U.S. Geological Survey
* [http://topotools.cr.usgs.gov/gmted_viewer/ Global Multi-resolution Terrain Elevation Data 2010 (GMTED2010)] by the U.S. Geological Survey
* [https://web.archive.org/web/20160304055004/http://www.iapg.bgu.tum.de/9321785--~iapg~forschung~Topographie~Earth2014.html Earth2014] by [[Technische Universität München]]
* [https://sonny.4lima.de/ Sonny's LiDAR Digital Terrain Models of Europe]

{{DEFAULTSORT:Digital Elevation Model}}
[[Category:Digital elevation models| ]]