49
© 2016 Open Geospatial Consortium
2.5.1.1 Base Material Table BMT
A Base Material Table BMT is provided for run-time access by client applications. See section 5.1.3, Base Material Table for more details on the file format.
2.5.2 Composite Materials
This section provides additional description and details regarding the layered substrate structure to Base Materials, aka Composite Materials.
Each Composite Material consists of a primary substrate component, an optional surface component and one or more optional secondary substrate components. Each of these
components is in turn composed of one or more Base Materials described in the previous section. Components that are composed of two or more Base Materials are aggregates. Each Composite
Material has a primary substrate as a minimum. The primary and secondary substrates can be optionally assigned a thickness in meters. By definition, the surface substrate corresponds to
the first micrometer µm to millimeter mm of a Composite Material. The surface substrate does not change the nature of the primary substrate; its purpose is to differentiate the objects
primary substrate from its coating.
Each substrate is defined by a variable-size structure that references one or more Base Materials. Each Base Material is assigned a weight ranging from 1 to 100. The sum of the weights
assigned to the Base Materials of each component SHALL sum to 100
17
. For example, a
mixture aggregate of 75 sand and 25 soil, would be constructed as a Composite Material with a primary substrate component with Base Materials BM_SAND 75 weight and
BM_SOIL 25 weight. In this example, there is no surface substrate and no secondary substrates.
2.5.2.1 Composite Material Substrates
A substrate provides a means to describe the material composition of “hidden” materials located beneath or inside the surface of a feature. This information is not explicitly modeled using for
instance polygons; instead it is an essential characteristic of the material that makes up the modeled feature.
Consider a seabed consisting of a silt deposit Figure 2-6: Seabed Composite Material. Such a deposit might have a thickness of a few centimeters. In our model, it is considered too thick to
be considered the surface substrate of the seabed. In fact, below this silt deposit, there can be sand with a thickness of a few dozen centimeters, followed by rock of essentially infinite
thickness. A sonar device can use the thickness information provided by the Seabed Composite Material, to generate multiple echoes, corresponding to each substrate.
17
This is a requirement. The editor missed this requirement in Version 1 of the standard. This sentence will be restated in the next version as an official requirement.
50
© 2016 Open Geospatial Consortium
Figure 2- 6: Seabed Composite Material
As a second example, consider a half-filled refinery oil tank see Figure 2-7: Oil Tank Composite Materials.
Figure 2- 7: Oil Tank Composite Materials
In order to capture different thermal signatures for the top and bottom portions of the tank, a modeler uses two different Composite Materials:
For the top half of the tank, the modeler uses a Composite Material consisting of paint surface substrate, metal primary substrate and air secondary substrate.
51
© 2016 Open Geospatial Consortium
For the bottom half of the tank, the modeler uses a Composite Material consisting of paint surface substrate, metal primary substrate and oil secondary substrate.
Thermal Infrared Visible
Figure 2- 8: Thermal Simulation of Oil Tank Composite Materials
Note that since the metal substrate is several centimeters thick, it is not considered to be the surface substrate of the oil. Figure 2-8: Thermal Simulation of Oil Tank Composite Materials,
illustrates the different simulation responses for a FLIR and an OTW CDB client device for this particular example.
2.5.2.2 Composite Material Tables CMT
Kategori