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digital_elevation_models

Digital Elevation Model Support

The following web sites are repositories for digital elevation model data that can be used with TerreSculptor.

This page was last updated on October 03, 2011. The information regarding these sites should be current as of this date.

This list will be maintained and updated with information regarding the data file formats and their support with TerreSculptor.
Most DEM data is free for any use but be sure to check with each DEM site's data file usage policy before using any DEM data files for commercial purposes.

Unfortunately, many of the DEM data sites are operated by governments or organizations who are constantly changing their data file formats and changing their data sets and web site addresses.
Comments regarding DEM data site additions or corrections can be posted by registered users on the TerreSculptor forums.

Choosing the Proper DEM Resolution

Digital Elevation Model resolution is typically specified in arc-seconds or meters between sample points.
The resolution value is the spacing distance between each altitude sample point, which is the equivalent to each pixel in a heightmap or each vertex in a terrain mesh.
The spacing can also be thought of as the size of each terrain quad triangle-pair.
A 10 meter DEM file is therefore three times higher resolution than a 30 meter DEM file.
To obtain a satisfactory terrain resolution for use in video games a resolution between 1 and 10 meters is typically required.

Arc-seconds to Meters approximate conversion ratio for common resolutions:
30 arc-seconds = 900 meters (approximately 1 kilometer)
10 arc-seconds = 300 meters
3 arc-seconds = 90 meters
1 arc-second = 30 meters
1/3 arc-second = 10 meters
1/9 arc-second = 3 meters

Spacing as related to video game engine terrain meshes:

- A terrain mesh with an XY spacing of 128 and an engine unit of 1 unit = 1cm is a spacing of 128cm or a 1.28 meters DEM spacing.
- A terrain mesh with an XY spacing of 256 and an engine unit of 1 unit = 1cm is a spacing of 256cm or a 2.56 meters DEM spacing.
- A terrain mesh with an XY spacing of 512 and an engine unit of 1 unit = 1cm is a spacing of 512cm or a 5.12 meters DEM spacing.

- A terrain mesh with an XY spacing of 128 and an engine unit of 1 unit = 2cm (Epic UDK) is a spacing of 256cm or a 2.56 meters DEM spacing.
- A terrain mesh with an XY spacing of 256 and an engine unit of 1 unit = 2cm (Epic UDK) is a spacing of 512cm or a 5.12 meters DEM spacing.
- A terrain mesh with an XY spacing of 512 and an engine unit of 1 unit = 2cm (Epic UDK) is a spacing of 1024cm or a 10.24 meters DEM spacing.

- A DEM spacing of 1/9 arc second (3 meters) and an engine unit of 1 unit = 2cm (Epic UDK) is an XY spacing of 150 (128 is the closest power-of-two value).
- A DEM spacing of 1/3 arc second (10 meters) and an engine unit of 1 unit = 2cm (Epic UDK) is an XY spacing of 500 (512 is the closest power-of-two value).


DEM Data Sites

The following is a partial listing of DEM sites that host data files.


CGIAR - Consortium for Spatial Information

Main URL: http://srtm.csi.cgiar.org/
Resolutions: 3 arc-seconds (90 meter)
Formats: GeoTIFF, ArcInfo ASCII
TerreSculptor: currently not supported (ArcInfo ASCII support is currently under development)


Earth Explorer - USGS

Main URL: http://edcsns17.cr.usgs.gov/NewEarthExplorer/

Additional information will be added soon.


EROS - Earth Resources Observation and Science (EROS) Center

Main URL: http://eros.usgs.gov/#/Find_Data/Products_and_Data_Available/gtopo30_info
Resolutions: 30 arc-second (1 kilometer)
Formats: BIL (Motorola signed 16-bit integer with .hdr file)
TerreSculptor: import BIL with .hdr

Rename the .DEM file in the download to .bil and import it as BIL.
The .HDR text file contains the BIL file meta-information.

NOTE! Tests of the data files from this site show that they are incorrect and cannot be successfully loaded.
The .HDR file meta-information does not equal the data file contents.
This issue will be examined further and information posted here.


GeoBase - Canadian Digital Elevation Data

Main URL: http://www.geobase.ca/geobase/en/data/cded/index.html
Resolutions: vary from 0.75 arc-seconds (22 meter) to 12 arc-seconds (360 meter)
Formats: ASCII DEM
TerreSculptor: currently not supported (ASCII DEM support is currently under development)


NASA PDS Geosciences Node

MOLA - Mars Global Surveyor

Main URL: http://pds-geosciences.wustl.edu/missions/mgs/megdr.html
Resolutions: low
Formats: .img binary

The topography .img files can be manually loaded with the TerreSculptor Raw R16 importer.
Rename the .img file to .r16.
Proper .img file format support is coming soon.

Meg4 4 pixels per degree megt* is topology 1440×720 16-bit signed Mac
Meg16 16 pixels per degree megt* is topology 5760×2880 16-bit signed Mac
Meg32 32 pixels per degree megt* is topology 11520×5760 16-bit signed Mac
Meg64 64 pixels per degree megt* is topology 11520×5760 16-bit signed Mac
Meg128 128 pixels per degree megt* is topology 11520×5632 16-bit signed Mac

Polar 512 pixels per degree megt* is topology 12288×12288 16-bit signed Mac

Meg128 total 4×4 tile images for 46080×22528 x16bit = 2,076,180,480
The top and bottom strips are essentially useless as they are stretched due to projection so:
total 2×4 tile images for 46080×11264 = 519045120 x16bit = 1,038,090,240


NASA PDS Geosciences Node

Magellan - Venus Magellan GTDR Topographical Data records.

Main URL: http://pds-geosciences.wustl.edu/missions/magellan/gxdr/index.htm
Resolutions: low
Formats: .img binary

The topography .img files can be manually loaded with the TerreSculptor Raw R16 importer.
Rename the .img file to .r16.
Proper .img file support is coming soon.

Browse.img files are 512×512 with 2048 header.
f*.img files are 1024×1024 16-bit with 2048 header.


NED - USGS National Elevation Dataset.

Main URL: http://ned.usgs.gov/
Data viewer URL: http://seamless.usgs.gov/website/seamless/viewer.htm
Datasets: United States
Available resolutions:

NED 1 (1 arc-second = 30 meter)
Formats: ArcGrid, Bil, Bil_16 Integer, TIFF, GridFloat
TerreSculptor: import Bil 16-bit Integer and Gridfloat

NED 1/3 (1/3 arc-second = 10 meter)
Formats: ArcGrid, Bil, Bil_16 Integer, TIFF, GridFloat
TerreSculptor: import Bil 16-bit Integer and Gridfloat

NED 1/9 (1/9 arc-second = 3 meter)
Formats: ArcGrid, Bil, Bil_16 Integer, TIFF, GridFloat
TerreSculptor: import Bil 16-bit Integer and Gridfloat


SRTM - Shuttle Radar Topography Mission

Main URL: http://srtm.usgs.gov/

Requires onsite user account registration and login.
Additional information will be added soon.


Miscellaneous DEM URLs

digital_elevation_models.txt · Last modified: 2013/01/29 17:09 by dgreen

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