Digital elevation models

Doing some research on Digital Elevation Models, for making terrain maps.

SRTM

(Wikipedia, OSM Wiki) sourced from a space shuttle overflight in 2000. Comes in several flavours and sources.

Sources:

  • NASA source (download link). Original data. Version 2.1 is their latest, cleaned up by NGA. The NASA has some data voids, particularly at mountains and lakes. Documentation of the dataset.
    License: Data said to be fully open for any use; don’t have a specific reference.
  • CGIAR-CSI Data processed to remove voids. SRTM3 only. They publish it as “version 4.1”, version number reflects their data cleaning. Also available as an Amazon EBS volume.
    License: non-commercial with attribution.
  • HydroSHEDS. SRTM data with voids filled, SRTM3 only. Also vector data on watersheds. Technical documentation.
    License: “free for non-commercial use”
Details on NASA source:
SRTM1:
  • Resolution: 1 arc second, roughly 30m, z=12
  • Format: .HGT files, 3601×3601 per one degree square file. Each sample is 16 bits, height in meters (-32768 for no data). GDAL supports this format.
  • Coverage: Continental US, a bit of Alaska, and various US territories. Coverage map.
  • Size: 1117 files of 25 megs each, or 27 GB uncompressed. 2:1 compression with gzip.
SRTM3:
  • Resolution: 3 arc seconds, roughly 90m, z=10
  • Format: .HGT files as SRTM, 1201×1201 per one degree square file.
  • Coverage: global land mass from 60N to 56S. (Missing Antarctica, significant Northern parts of North America, Europe and Asia).  Coverage map.
  • Size: 14546 files of 2.8 megs each, or 39 GB. 2:1 compression with gzip.
SRTM30:
  • Resolution: 30 arc seconds, roughly 1km, z=7
  • Coverage: global from 90N to 60S. (Missing Antarctica). Coverage map. See also GTOPO30.

National Elevation Dataset

Wikipedia. Also NED FAQ. USGS data from various sources.
  • Resolution: 1 arc-second (z=12), 1/3 arc-second (z=14), and 1/9 arc-second (z=15).
  • Format: accessible via WMS. Data downloads provided in ArcGrid format and “float format”, looks like 32 bits / sample.
  • Coverage: United States and Mexico only. 1/3 for the 48 states, 1/9 in some detailed places. Coverage maps: 1 arcsecond1/31/9
  • Size: files appear to be double the size of equivalent SRTM data. Rough guess: 50GB for 1 arc-second, 450GB for 1/3 arc-second.

Viewfinder Panoramas

Eclectic collection of more detailed / patched data than SRTM in certain spots. Unclear licensing.

ASTER GDEM

Joint NASA/Japan METI project, produces a 30m DEM. (Wikipedia, OSM Wiki) Has coverage between 83N to 83S and some holes filled compared to SRTM. Some question on quality; the data comes with a “quality assessment file”. May be free to use, but some concern on the OSM Wiki that its license is not consistent.

OpenDEM

Well intentioned but small project to provide better DEM data. Some useful notes.

GMTED2010

USGS project. Global data: 90S to 83N. 7.5 arc second (30m). Looks to be a combination of SRTM data and other sources. License is presumably public domainish. The metadata page says “Metadata access constraints: No restrictions, All GMTED2010 data products and associated metadata are publically available”.