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The SEDRIS Data Representation Model
APPENDIX A - Classes Geometry Model Instance |
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An instance of this DRM class specifies a single case of the existence of a <Geometry Model> within a given transmittal, including variations or specialization unique to that case. In particular, a <Geometry Model Instance> is used to transform a <Geometry Model> into the spatial reference frame of another <Geometry Model> or that of an <Environment Root>.
Consider a <Model> of a building, consisting of a <Geometry Model> describing its geometric representation, where the <Model> is described in an LSR 3D spatial reference frame.
To instance this <Model> into an <Environment Root>, the spatial reference frame of which is 3D geodetic, the data provider constructs a <Geometry Model Instance> with a <World Transformation> component, and incorporates it into the <Geometry Hierarchy> of that <Environment Root>. The <World Transformation> specifies the <GD Location 3D> at which the <Model>'s 0, 0, 0 coordinate will be instanced, together with any other transformation information required to orient and scale the <Model> properly.
Consider a <Geometry Model> describing the rotor of a helicopter, and intended for use within a larger <Geometry Model> of the entire helicopter. Both are defined in 3D LSR spatial reference frames.
The helicopter model will contain a <Geometry Model Instance> of the rotor model, with an <LSR Transformation> component containing a <Rotation> instance with a <Rotation Control Link>. The <LSR Transformation> specifies both the transformation required to position the rotor within the helicopter model, and the <Variable> within the larger helicopter <Model> that will be plugged into the rotor <Model>'s internal <Variable> for angle of rotation.
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An association between a <Geometry Hierarchy> instance and a <Feature> instance indicates that the <Geometry Hierarchy> and the <Feature> are alternate representations of the same environmental object.
An association between two <Geometry Hierarchy> instances indicates that they are alternate representations of the same environmental object.
An association from a <Hierarchy Summary Item> instance to a <Geometry Hierarchy> indicates that the <Hierarchy Summary Item> summarizes that <Geometry Hierarchy>.
An association from a <Reference Surface> instance to a <Geometry Hierarchy> indicates that the <Geometry Hierarchy> organizes the geometric objects that specify the resolution surface of the <Reference Surface>.
An association from a <Geometry Model Instance> instance to a <Geometry Model> indicates that the <Geometry Model Instance> instances that particular <Geometry Model>.
This allows a <Geometry Model Instance> to be conformal. If present, the <Conformal Behaviour> component is applied after any <Transformation> that is present.
This positions and orients the given <Geometry Model Instance> in the target spatial reference frame.
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