(Under construction)
| Two types of terrain data
are commonly used in wireless communications system design: terrain
elevation data and land use/land cover data.
Terrain elevation data are also referred to as digital terrain models (DTM's) and digital elevation models (DEM's). They are typically delivered in raster (grid) format. Terrain elevation data generally indicate the elevation of the bald or bare earth. Supplementary data are used to indicate the height of foliage and man-made structures in the region of interest. Low resolution versions of such supplementary data often take the form of clutter property models which are referred to particular land use/land cover types (see below). High resolution forms of such data take the form of canopy models and building databases, which are referred to either geodetic coordinates or the postings used for the terrain elevation data. In the past, wireless system planners often obtained low resolution terrain elevation data for wide areas by scanning or digitizing government topographic maps. More recently, planners have been able to obtain such data through direct access to government cartographic databases. Although such access is essentially free of charge in the United States, other jurisdictions typically charge a substantial fee. When existing terrain elevation databases lack the required accuracy and resolution, terrain elevation data can be obtained by applying photogrammetric methods or related processes to stereo pairs produced using either spaceborne or airborne cameras or imagers. Very high resolution terrain data can be obtained using either advanced photogrammetric methods or airborne sensors such as LIDAR. The cost of terrain elevation data rises very rapidly as the accuracy and resolution increase, however. As one might expect, production of terrain elevation data for urban environments is typically much more challenging than for either suburban or rural environments. Land Use/Land Cover (LULC) data, are also referred to as thematic maps. In the past, wireless system planners often obtained low resolution LULC for wide areas by scanning or digitizing government topographic maps. Because such data is often rendered obsolete by the rapid pace of development, planners have sought more current sources. In recent years, Landsat, SPOT, and IRS-1C panchromatic and/or multispectral satellite imagery has been used to provide a cost-effective solution. The first step in the classification process is to identify the LULC classes to be distinguished in the imagery. Typically, this may range between 6 and 20 classes. Low resolution multispectral imagery is useful for distinguishing between rural land cover types (bare earth, vegetation, snow/ice, water, etc.) while high resolution panchromatic imagery is useful for distinguishing between urban land use classes. While automated classification methods are employed where possible, accuracy requirements often demand that a sizeable proportion of the classification process be conducted manually. Although LULC data is sometimes delivered as raster (grid) data, it is more typically delivered as vector data which describe a set of polygons which enclose homogeneous regions. In practice, only polygons above a particular size (the minimal mapping unit) are included in the LULC database. Road and transportation network data are a third
class of data which is often included in terrain data packages.
Such data is typically delivered as vector data. USGS DLG (Digital
Line Graph) data includes waterways (streams, lakes, etc), and political
boundaries, as well.
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Some Terrain Data Providers General Information Bruce Gittings's Digital Elevation Data Catalogue Index
of Available Digital Terrain Data for GIS
Some Sources of Government Terrain Data USGS National Mapping Information (USA) National Imagery and Mapping Agency (USA) Natural Resources Canada (Canada) Australian Surveying
and Land Information Group (AUSLIG) (Australia)
Some Commercial Data Providers Intermap (Canada) Radarsat International (Canada) Space Imaging Corp. (Colorado) i3 (Colorado) Vexcel Corp. (Colorado) Marconi (Canada) ISTAR (France) BKS Aerial Surveys (UK) Infoterra (UK) Infoterra - Geostore (UK) DMTI Spatial (Canada) Computamaps (South Africa) Siradel (France)
Some LIDAR Data Providers (under construction)
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If you have comments, suggestions, corrections, or contributions, please email me at dmichelson@ieee.org
http://members.shaw.ca/propagation/terrain.html
Last updated: 20 May 2002