Digital elevation model

Draft

“A digital elevation model (DEM) is a digital representation of ground surface topography or terrain. It is also widely known as a digital terrain model(DTM). A DEM can be represented as a raster (a grid of squares) or as a triangular irregular network.” (Wikipedia, retrieved 17:39, 12 May 2010 (UTC)).

A digital surface model (DSM) on the other hand includes buildings, vegetation, and roads, as well as natural terrain features. The DEM provides a so-called bare-earth model, devoid of landscape features. While a DSM may be useful for landscape modeling, city modeling and visualization applications, a DEM is often required for flood or drainage modeling, land-use studies, geological applications, and much more. (Wikipedia, retrieved 17:39, 12 May 2010 (UTC)).

Models and file Formats

Both digital elevation and surface models can either be represented as raster or vector graphics.

• Raster data can present either just images (as in any image format like *.jpg*) or include specific data about a cell.
• Vector data either can be points (locations), lines or polylines (e.g. for topographics lines or roads), or polygons.

“Additional non-spatial data can also be stored along with the spatial data represented by the coordinates of a vector geometry or the position of a raster cell. In vector data, the additional data contains attributes of the feature. For example, a forest inventory polygon may also have an identifier value and information about tree species. In raster data the cell value can store attribute information, but it can also be used as an identifier that can relate to records in another table.” (Wikipedia, retrieved 17:39, 12 May 2010 (UTC)).

Digital elevation models

USGS DEM

“The USGS DEM standard is a geospatial file format developed by the United States Geological Survey for storing a raster-based digital elevation model. It is an open standard, and is used throughout the world. It has been superseded by the USGS's own SDTS format but the format remains popular due to large numbers of legacy files, self-containment, relatively simple field structure and broad, mature software support.” (Wikipedia, retrieved 17:39, 12 May 2010 (UTC))

SDTS

“The The Spatial Data Transfer Standard (SDTS) is a robust way of transferring earth-referenced spatial data between dissimilar computer systems with the potential for no information loss. It is a transfer standard that embraces the philosophy of self-contained transfers, i.e. spatial data, attribute, georeferencing, data quality report, data dictionary, and other supporting metadata all included in the transfer.” (USGS, retrieved 17:39, 12 May 2010 (UTC))

DTED

“DTED (or Digital Terrain Elevation Data) is a standard of digital datasets which consists of a matrix of terrain elevation values. This standard was originally developed in the 1970s to support aircraft radar simulation and prediction.” (DTED (Wikipedia, retrieved 17:39, 12 May 2010 (UTC))

Other/combined models

SRTM

“The Shuttle Radar Topography Mission (SRTM) is a partnership between NASA and the National Geospatial-Intelligence Agency (NGA). Flown aboard the NASA Space Shuttle Endeavour (11-22 February 2000), SRTM fulfilled its mission to map the world in three dimensions.” (EORS.usgs.gov)

Advanced Spaceborne Thermal Emission and Reflection Radiometer

• Advanced Spaceborne Thermal Emission and Reflection Radiometer. “ASTER provides high-resolution images of the Earth in 15 different bands of the electromagnetic spectrum, ranging from visible to thermal infrared light. The resolution of images ranges between 15 to 90 meters. ASTER data are used to create detailed maps of surface temperature of land, emissivity, reflectance, and elevation.” (http://en.wikipedia.org/wiki/Advanced_Spaceborne_Thermal_Emission_and_Reflection_Radiometer[ Wikipedia], retrieved 17:39, 12 May 2010 (UTC))

General pupose 3D formats

• See 3D file formats

Available terrain maps

STRM

The Shuttle Radar Topography Mission (SRTM) Maps.

Download links:

• directory. Read What_are_these.pdf first. Can be imported to ARCInfo with a little work (not tested)

GTOPO30

GTOPO30 is a global digital elevation model (DEM) of the whole world with a horizontal grid spacing of 30 arc seconds (approximately 1 kilometer). GTOPO30 was derived from several raster and vector sources of topographic information.

• GTOPO30 (Wikipedia)

Download links:

• GTOPO30 (US Geological survey EROS Data Center)
• GTOPO30 FTP Server
• Documentation about the formats

Links

Overviews

• Digital terrain model (Wikipedia)

Visualization and GIS

(these are related subjects)

• Geovisualization (Wikipedia)
• Geographic information system (GIS).
• Geographic information science
  • Geoinformatics
  • GeoComputation
• Web map server

Overviews and indexes of File formats

• GIS file formats (Wikipedia)
• GISDataDepot - GIS Data Formats
• Everything You Want To Know About SDTS! (Geo community)

Actors

• Open Geospatial Consortium
  • OpenGis.net repository of schemas and formats, etc.
  • Open Geospatial Consortium (Wikipedia)
• ISO/TC 211 Geographic information/Geomatics

Online maps to look at

(some can show relief).

• Web Map Services

• Maps-For-Free.com. Allows to display various Layers on either satellite, terrain, relief or OSM view. Allows to take a picture (jpg).

• GloVis (USGS Global Visualization) is an online search and order tool for selected satellite data. It includes

• WIST (Warehouse Inventory Search Tool) is a web-based client to search and order earth science data from various NASA and affiliated centers, e.g. GloVis.

• MRTWeb combines familiar capabilities of the USGS Global Visualization Viewer (GloVis) and the downloadable MODIS Reprojection Tool (MRT)

Software

Viewing

• TerraLook (Wikipedia) a free satellite image viewing tool, developed by Sujoy Chaudhuri of Ecollage, India.
• Google Earth (Wikipedia)

Multipurpose

• ArcGIS (Wikipedia) Commercial group of geographic information system (GIS) software products produced by ESRI.

To sort out

• Geo-Spatial Data Acquisition Homepage
• SRTM Homepage
• SRTM30 Plus Homepage
• Terrainmap Homepage
• More information about available DEM data
• More information about DEM by Spot Image
• http://emrl.byu.edu/gsda/data_dem_obtain.html
• http://www.webgis.com/srtm30.html
• NASA World Wind

Printing elevation models

The outline of the workflow is the following:

1. Get a model
2. Translate it to STL (this may need passing through an intermediary format)
3. Make the model manyfolded with a flat bottom
4. Slice and print it

Creating STL from elevation maps with gdal

Installation under Ubuntu 16x

Install the gdal library

sudo apt-get install libgdal-dev
sudo apt-get install gdal-bin

Test if something is there:

ogrinfo

Install the python interface (?)

sudo apt-get install python-gdal

Install the gdal python library

sudo easy_install gdal