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Although the user
interface is simple, the algorithms behind the software are very detailed. The
following components are involved and explained briefly:
TERRAIN
MODELING
The terrain
model incorporates the full effects of solar shadowing, multiple reflections, and
re-radiation of geometric features. Each triangular element (or facet) of the terrain
has a view factor to background, sky, and other elements. The view factors are
calculated by a voxel-based ray-tracing technique which casts rays from each element. Rays
which do not encounter another model element "see" default background or sky
surfaces. The total radiation on each element will be the net result of emitted radiant
energy, incoming solar radiance, and incoming radiant energy (reflected or emitted from
other elements).
| Starting with a
mesh of the area to be modeled, elements of similar terrain are grouped into parts and
assigned to the correct terrain type. For example all the elements representing the
road are assigned to a road part.
Available
terrains and subcategories are:
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Asphalt-
Country road, highway bridge, interstate road, parking lot, runway.
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Concrete-
Heavy pad, highway bridge, interstate road, parking lot, runway, sidewalk
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Foliage-
Grass (tall/ short), trees (coniferous, deciduous, mixed). These all have adjustable
degrees of coverage, moisture, and growth factor settings.
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Snow- Fresh,
old-dry, rained upon, surface melted, driven on, late in season, tundra, undisturbed.
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Swamp- The
swamp model has adjustable dew mass, growth factor, and cover factor.
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Layered- For
example: top layer is snow and bottom layer is asphalt.
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Soil-
Average, clay, desert sand, gravel, loam, peat, sandy, rocky field. The soil has
adjustable moisture settings.
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Water- Clear,
turbid. The depth can be adjusted for water.
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| Each terrain
element is treated as a one-dimensional heat and mass transfer nodal model consisting of 1
to 26 nodes. The temperature of each layer of terrain is computed using a nodal energy
balance. The captured physical processes include convection between the air and ground;
conduction through the soil layers; mass transfer of moisture in soil; residual mass
and flow rates of dew on foliage. The example shows approximately how this works. |
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