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'), 10m ('Profile') and 2m ('Profile-plus') 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 Ordnance Survey NTF Raster DEM format from the Open file dialogue.
Contour data are also distributed by the Ordnance Survey derived from their 1:50k maps ('panorama') and 1:10k maps ('profile').
These are also distributed in NTF format and may be imported into LandSerf by selecting the Ordnance Survey NTF Vector file
format.
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 25m DEM of the British Isles to UK higher educational institutions along with some selected LiDAR DEMs. The 25m DEM 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.
There are also various providers of global elevation data including the UK (see below). In many cases these data will be
referenced using global latitude/longitude coordinates. Such data should be reprojected onto the UK National Grid by selecting
the appropriate option from from LandSerf's Transform->Reproject menu.
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. The USGS now distribute their National Elevation Dataset (NED) - a continually updated seamless 30m DEM of the United States. Details can also be found in an article in the January 2002 edition of Photogrammetric Engineering and Remote Sensing.
Additionally available from the USGS are parts of the global Shuttle Radar Topography Mission (SRTM) dataset (see srtm.usgs.gov and www2.jpl.nasa.gov/srtm). Elevation products from this mission include 90m resolution DEM of the American continent and a 30m resolution coverage of the US.
The easiest way to download these data is to use the USGS's seamless.usgs.gov
website that allows arbitrary regions to be selected from the US and some other global sites. Also available from the same
site are selected landcover, vector and orthophoto coverages of the US. To import raster data from this site into LandSerf,
select the BIL (for integer data), GridFloat (for floating point data) or TIFF (for images) format from the USGS pages and
import using the relevant format in LandSerf. Note that all data are georeferenced using global latitude/longitude coordinates, and
should therefore be reprojected onto a planar UTM coordinate system using the appropriate option from the
Transform->Reproject menu.
The USGS also provided their older tiled '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 or 'USGS Native DEM'
format (e.g. see www.cs.arizona.edu/topovista/sdts2dem/
for some downloadable converters.
The principal advantage of these older data is that being tiled they correspond to other datasets produced by the USGS
such as their Digital Raster Scanned topographic maps.
One of the most useful global coverages of elevation data is provided by the Shuttle Radar Topography Mission (SRTM) dataset
(see www2.jpl.nasa.gov/srtm). Elevation data at 3 arc-second resolution
(about 90m E-W at the equator) are available for the Americas, Europe, parts of Asia, Africa and Australia from
ftp://e0srp01u.ecs.nasa.gov/srtm/version2/. These can be imported
directly into LandSerf by selecting the SRTM format when opening a raster. Note that as with other global datasets, after import, the
data should be reprojected into some planar projection such as UTM (select the appropriate option from the
Transform->Reproject menu). Additionally, SRTM data are likely to contain several 'voids' where the sensor was unable
to record an accurate elevation. These can be removed by selecting Void removal from the Transform menu.
See the guide how to import SRTM data for further details.
Coarser resolution global elevation at approximately 1km resolution are available from the freely available
GTOPO30 dataset. These data are compiled from a variety
of sources and include the entire global landmass (bathymetric data are not included in this dataset, but see below for alternatives).
To import GTOPO30 data, extract the files from the compressed tar file (Windows users make sure that if you are using WinZip to do this, that 'TAR file smart
CR/LF conversion' is not set). Select GTOPO30 as the file format in LandSerf to import the .dem file.
Bathymetric (see floor) data at a 2 minute resolution are freely available in the form of the ETOPO2 V.2 dataset. Data are distributed in ArcGIS ASCII grid format so can be directly imported into LandSerf.
The SRTM30Plus global dataset provides an integration of SRTM data covering global landmasses, bathymetic data for sea floor surfaces and GTOPO30 data for latitudes above +-80 degrees. Data are tiled into 33 regions of the globe at a resolution of 30 arc-seconds (~1km) and are stored in the same format as SRTM data so can be imported directly into LandSerf.
A number of freely available sources of landcover and remote sensing are available for much of the globe. For both, http://glcfapp.umiacs.umd.edu:8080/esdi provides a good start and can be used to provide data as georeferenced GeoTiff files that can be imported directly into LandSerf.
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 useful source of information is the 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 'at' city.ac.uk) with details of file formats, data availability etc.