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The way in which you import elevation models into LandSerf will depend on the location and resolution of the surface you wish to model.
In the UK, the most widely used DEM coverage is provided by the Ordnance Survey (www.ordnancesurvey.gov.uk).
They provide DEMs at 50m ('Panorama') and 10m ('Profile') resolutions for Britain. DEMs from
the Ordnance Survey are usually provided in National Transfer Format (NTF V.2). Data in this format can be immediately
imported into LandSerf by selecting the Import->NTF option. LandSerf cannot currently import data in DXF format
(also used by Ordnance Survey for distributing some of their data).
The UK Environment Agency (www.environment-agency.gov.uk) provide 2m resolution LiDAR DEMs for many coastal and inland areas in England and Wales, especially for areas susceptible to flooding. These are usually provided in ArcGIS ASCII raster format and so can be directly imported into LandSerf.
The LandMap project, (www.landmap.ac.uk) provides a free 30m DEM of the British Isles to UK higher educational institutions. It is based on multiple passes of the ERS SAR sensor. Data can be downloaded in ArcGIS ASCII raster format, so can therefore be imported directly into LandSerf.
Alternative providers of elevation data for the UK include EDX (www.edx.com)
who provide a comprehensive 50m resolution coverage. To import EDX data, you will first need to convert their proprietary
binary format into ASCII. This can be done using their supplied converter GBCNV.EXE. The result should be a
file called something.asc which can be imported into LandSerf using the Import->EDX
option.
The main provider of elevation data for the US is the United States Geological Survey (USGS), who provide DEMs (and other digital spatial data) at a variety of scales and resolutions. Many of these data can be downloaded over the internet via their Geodata web site. Here you will find DEMs at 30m resolution for most of the continental US.
The USGS now distribute their National Elevation Dataset (NED) - a
continually updated seamless 30m DEM of the United States. The NED web site allows you to navigate graphically around the
dataset selecting any arbitrary region using the mouse. Details can also be found in an article in the January 2002
edition of
Photogrammetric Engineering and Remote Sensing. The easiest way to import data from NED into LandSerf is to select the
BIL format (binary integer) from the USGS pages and import as 'ArcGIS binary image' in LandSerf. However, note that these
data use geographical coordinates (latitude/longitude). To perform meaningful analysis on the DEMs, they should be reprojected
onto a planar coordinate system in metres. For small areas (or for areas where absolute georeferencing is not crucial),
the boundary of the DEM can be converted into UTM coordinates and the grid resolution set to 30m (see for example
www.ngs.noaa.gov/cgi-bin/utm_getut.prl for an
online converter).
Alternatively, if you have access to ArcGIS, you can reproject the entire DEM into UTM coordinates before exporting as
as an ASCII raster for direct import into LandSerf.
The USGS also provided their older '7.5 minute' DEMs in SDTS format. These can be found by selecting the '1:24k DEM' option from the Geodata web site. If you download data in this format you will next need to convert these files into a form readable by LandSerf. The easiest way to do this is to use one of the utilities provided by the USGS to convert SDTS into ArcGIS raster format (e.g. see software.geocomm.com/translators/sdts for some downloadable converters, or download directly the DOS program sdts2arc.exe from ftp://ftp.blm.gov/pub/gis/sdts/dem.
Data for other areas of the world are likely to be provided in a range of formats. You may wish to consult the details on file formats to see how they may be imported. Another very useful source of information is the excellent Virtual Terrain Project site, which includes a list of international elevation model sources.
If you wish to see instructions on how to import elevation data for your own region of interest, please email me (jwo@soi.city.ac.uk) with details of file formats, data availability etc.
