Digital elevation model: Difference between revisions

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== Introduction ==


{{quotation|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.}} ([http://en.wikipedia.org/wiki/Digital_terrain_model Wikipedia], retrieved 17:39, 12 May 2010 (UTC)).
{{quotation|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.}} ([http://en.wikipedia.org/wiki/Digital_terrain_model 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. ([http://en.wikipedia.org/wiki/Digital_terrain_model 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. ([http://en.wikipedia.org/wiki/Digital_terrain_model Wikipedia], retrieved 17:39, 12 May 2010 (UTC)).
See also:
* [[3D printing of digital elevation models]] (various methods)
* [[Maperitive for laser cutting and 3D printing]] (using OpenStreetMap)


== Models and file Formats ==
== Models and file Formats ==
-- This section badly needs revision and updating - [[User:Daniel K. Schneider|Daniel K. Schneider]] ([[User talk:Daniel K. Schneider|talk]]) 10:41, 21 March 2017 (CET)


Both digital elevation and surface models can either be represented as raster or vector graphics.
Both digital elevation and surface models can either be represented as raster or vector graphics.
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* [ftp://edcftp.cr.usgs.gov/pub/data/gtopo30/global/ GTOPO30 FTP Server]
* [ftp://edcftp.cr.usgs.gov/pub/data/gtopo30/global/ GTOPO30 FTP Server]
* [http://eros.usgs.gov/#/Find_Data/Products_and_Data_Available/gtopo30/README Documentation about the formats]
* [http://eros.usgs.gov/#/Find_Data/Products_and_Data_Available/gtopo30/README Documentation about the formats]
; Other
* [http://www.viewfinderpanoramas.org/ Viewfinder Panoramas] (many selected area tiles of the world)


== Links ==
== Links ==
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; Multipurpose
; Multipurpose
* [http://en.wikipedia.org/wiki/ArcGIS_Desktop ArcGIS] (Wikipedia) Commercial group of geographic information system (GIS) software products produced by ESRI.
* [http://en.wikipedia.org/wiki/ArcGIS_Desktop ArcGIS] (Wikipedia) Commercial group of geographic information system (GIS) software products produced by ESRI.
=== Other kinds of 3D representations of 2D pictures ===
* [https://www.thingiverse.com/thing:74322 Customizable Lithopane] (but followup other projects referred to)


=== To sort out ===
=== To sort out ===
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* http://www.webgis.com/srtm30.html
* http://www.webgis.com/srtm30.html
* [http://en.wikipedia.org/wiki/NASA_World_Wind NASA World Wind]
* [http://en.wikipedia.org/wiki/NASA_World_Wind NASA World Wind]
== Printing elevation models ==
The outline of the workflow is the following:
# Get a model
# Translate it to STL (this may need passing through an intermediary format)
# Make the model manyfolded with a flat bottom
# Slice and print it
=== Creating STL from elevation maps with gdal and phstl.py ===
==== 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
Download the phstl.py script
* Either take the package from https://github.com/anoved/phstl , or
git clone https://github.com/anoved/phstl.git
Copy the script to some place that is in the PATH,e .g. ~/bin or /usr/local/bin
==== Transforming a geoTIFF to STL ====
Get an example file, e.g. from [http://srtm.csi.cgiar.org/ CGIAR-CSI]<ref>Quote: "The CGIAR is a global partnership dedicated to reducing rural poverty, increasing food security, improving human health and nutrition, and ensuring more sustainable management of natural resources. The '''Consortium for Spatial Information''', CSI, is the CGIAR community of geo-spatial scientists that promotes and practices the application of spatial science to achieving these goals most effectively." http://www.cgiar-csi.org/ Feb 2017</ref> that provide elevation models for the whole world.
You can select a square in an area of interest. However this will create huge files. Most of Sicily sits in a square that is represented by a 72 GB tiff file. Translated this produced a 565 GB (!) STL File, which will be very difficult to handle.
'''Transform the tif into a non printable STL with phstl.py'''
Example:
phstl.py srtm_39_05.tif sicily.stl
Since the STL was too huge I did not pursue this. Maybe cropping the tif file before translating could be a solution, but which program can do it without deleting the height information data ?
=== Using Terrain2STL ===
Terrain2STL is an online service that allows selecting a square on Google maps. From the coordinates it then will extract a region from the Nasa/cgiar-csi data and produce the STL. Quote:  {{quotation|Terrain2STL is a free-to-use service, but if you want to help support the site, donations are welcome. Terrain2STL creates STL files using the SRTM3 dataset from 2000, which has a resolution of about 90 meters on the equator.}} ([http://jthatch.com/Terrain2STL/ Terrain2STL home page], feb 2017)
It only will need some cropping and a little repair, e.g. something that Netfabb Studio can handle very well.
* http://jthatch.com/Terrain2STL/
I tested this service and it works really well, e.g. I printed the Teide and Caldera Blanca volcanoes. The only caveat is the 90m resolution of the SRTM3 data set. The Caldera Blanca is a small 300m mountain on Lanzarote and did not come out in a very interesting way. The Teide (including the old huge caldera) created a fine enough model.
=== Hills ===
Hills is another package that can generate 3D models of areas in STL format of the earth's surface using SRTM 90m elevation data from CGIAR-CSI w(see http://srtm.csi.cgiar.org/).
This command line tool is programmed in Haskel and requires some installation. It's advantage with respect to phstl.py is that it can directly extract the right squares before doing the STL translation.
==== Installation under Ubuntu ====
To install Haskel and cabal
sudo apt install cabal-install
To install hills:
cabal update
cabal install hills
I found the program in ~/.cabal/bin/ so you might add this to your path:
* Edit ~/.bashrc
* Prepend ''/home/your_login/.cabal/bin'' to :$PATH, e.g.
export PATH=/home/_____/.cabal/bin:$PATH
==== Using hills ====
Get a data file from CGIAR-CSI. The earth is divided into squares.
[[File:SRTM_Data_Search_-_2017-03-03_11.49.33.png|thumb|800px|SRTM Data Search allows to identify squares that you then can dowload]
* Either use the website where you can select the squares (see figure above)
* Or write down the square number and change the URL below. 38_03 represents parts of Western Switzerland, French Haut-Savoie etc. (are where University of Geneva is located)
wget http://srtm.csi.cgiar.org/SRT-ZIP/SRTM_v41/SRTM_Data_ArcASCII/srtm_38_03.zip
unzip srtm_36_01.zip
You now should have the following 150 GB file
150147952 Nov 24  2008 srtm_38_03.asc
From there you can extract rectangles that will be translated to STL models. You need the following information
* Coordinates of the center, defined as decimal latitudes and longitudes. North of the equator is positive, south is negative. East from Greenwich is positive, west is negative. A good trick is to ask Google. E.g. ''longitude Geneva'' gives:
46.2044° N, 6.1432° E
Exactly what we need to extract terrain around geneva. If you cannot retrieve this directly from google search, consider


== Bibliography, links and footnotes ==
== Bibliography, links and footnotes ==
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[[Category:3D]]
[[Category:3D]]
[[Category: 3D printing]]
[[Category:Cartography]]
[[Category:Cartography]]

Latest revision as of 14:34, 18 January 2018

Draft

Introduction

“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)).

See also:

Models and file Formats

-- This section badly needs revision and updating - Daniel K. Schneider (talk) 10:41, 21 March 2017 (CET)

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

General pupose 3D formats

Available terrain maps

STRM

The Shuttle Radar Topography Mission (SRTM) Maps.

Download links:

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.

Download links:

Other

Links

Overviews

Visualization and GIS

(these are related subjects)

Overviews and indexes of File formats

Actors

Online maps to look at

(some can show relief).

  • 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.

Other kinds of 3D representations of 2D pictures

To sort out

Bibliography, links and footnotes

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