Материал: part03

C.27.1.1 Surface Mesh Module Attribute Descriptions​

C.27.1.1.1 Surface Sequence​

Surface Sequence (0066,0002) describes individual surfaces. There is no requirement that a surface be contiguous. For example,​ both kidneys could be described as a single surface consisting of 2 non-contiguous areas.​

C.27.1.1.2 Surface Processing​

Surface Processing refers to methods of surface modification such as smoothing operations, which remove redundant vertices, or​ decimation, which will modify the resolution of the surface. If a surface has been subject to processing, a description of the process​ may be provided in Surface Processing Description (0066,000B).​

C.27.1.1.3 Recommended Presentation​

Recommended Presentation Opacity (0066,000C) is a fraction between 0.0 and 1.0 encoded as a float value representing the​ blendingproportionoftherenderingofthesurfacerelativetounderlyingfeatures.Avalueof0.0isinterpretedascompletetransparency,​ while a value of 1.0 is interpreted as fully opaque.​

The Recommended Presentation Type (0066,000D) Attribute provides guidance as to the default presentation of the Surface.​

Defined Terms:​

SURFACE​ Renderthesurfaceasasolid,applyingtheopacityasspecifiedintheRecommendedPresentationOpacity(0066,000C)​ Attribute.​

WIREFRAME​Represent the surface as a series of lines connecting the vertices to form the defined primitive faces.​ POINTS​ Represent the surface as a cloud of points.​

C.27.1.1.4 Finite Volume​

The Finite Volume (0066,000E) Attribute shall be YES when the surface mesh generated by the primitives is topologically closed and​ has an inside and an outside. A surface mesh is closed if it has no rim (every facet has a neighboring facet along each edge). Fig-​ ure C.27.1.1-1 shows a surface that is not closed on the left, and a closed and waterproof version of the same shape on the right:​

In the mesh on the left, the triangles on the front-side and the one on the bottom have no neighbors. The surface is topologically not closed.

Two possible solutions are shown on the right.

Figure C.27.1.1-1. Finite Volume Illustration​

Not all closed surfaces contain a finite volume, for example if the surface self-intersects. Such surfaces do not contain a finite volume.​ A surface is not required to be contiguous.​

A value of NO indicates that the surface is not closed.​

A value of UNKNOWN indicates that the transmitting application did not determine if the surface is closed.​

- Standard -​

C.27.1.1.5 Manifold​

The Manifold (0066,0010) Attribute shall be YES when the surface mesh is a manifold.​

A surface embedded into an n-dimensional vector space is called an n-1 manifold if it resembles an n-1 dimensional Euclidean space​ in a neighborhood of every point lying on the surface. This means that every point has a neighborhood for which there exists a​ homeomorphism mapping that neighborhood to the n-1 dimensional Euclidean space.​

A sphere in 3-space is a 2-dimensional manifold: Every point has a neighborhood that looks like a plane.​

Figure C.27.1.1-2 shows examples of a surface that is not a manifold is given below:​

The two tetrahedrons in the left image share one face and three edges (marked red). The points along the shared edges are non-manifold, since the edges belong to three triangles: The neighbors of each point on these edges are lying in three different planes.

The same shape can be modeled with a manifold surface by leaving out the triangle separating the tetrahedrons.

Doubled vertices spanning two topologically unconnected tetrahedrons would also result in manifold surfaces.

Figure C.27.1.1-2. Manifold Illustration​

A value of NO indicates that the surface is not a manifold.​

A value of UNKNOWN indicates that the transmitting application did not determine if the surface is a manifold.​

C.27.1.1.6 Surface Points Normals Sequence​

SurfacePointsNormalsSequence(0066,0012)providesanexplicitnormalvectorforeachpointinSurfacePointsSequence(0066,0011)​

in Point Coordinates Data (0066,0016).​

If an Item of Surface Points Normals Sequence (0066,0012) is present the normal for a primitive may be computed by combining the​ normals for each vertex making up the primitive.​

If an Item of Surface Points Normals Sequence (0066,0012) is not present the normal for a primitive shall be computed by computing​ the cross product of two segments of the primitive. The segments shall be formed using the primitive definitions as specified within​ the Surface Mesh Primitives Sequence (0066,0013). The primitive vertices are taken in the order specified within Long Primitive Point​ Index List (0066,0040). Figure C.27.1.1-3 shows the method to compute the normal:​

- Standard -​

k

i

j

n = ij x jk

Figure C.27.1.1-3. Triangle Normal Computation​

The computed normal shall point in the direction of the outside of the surface.​

ForTriangleStriporTriangleFanprimitives(seeSectionC.27.4),thenormaldirectionisdeterminedbytheorderofthepointsreferenced​ by the first triangle in the strip or fan. When constructing a list of triangles from a triangle strip, the order of the points must be flipped​ for every second triangle to maintain consistency in the normal directions for the triangle.​

C.27.2 Points Macro​

Table C.27-2 specifies the Attributes of the Points Macro.​

Table C.27-2. Points Macro Attributes​

C.27.2.1 Points Macro Attribute Descriptions​

All Attributes within this Module containing points or vectors are in x-y-z order. If multiple elements are encoded, the ordering is​ x1,y1,z1,…,xn,yn,zn.​

ThepointsareinthecoordinatesystemidentifiedbytheFrameofReferenceUID(0020,0052).Tomapthesepointsintothecoordinate​ system of another SOP Instance a Spatial Registration Instance can be used.​

- Standard -​

C.27.2.1.1 Point Coordinates Data​

When referencing individual points the index of the first point shall be 1.​

C.27.3 Vectors Macro​

Table C.27-3 specifies the Attributes of the Vectors Macro.​

Table C.27-3. Vectors Macro Attributes​

C.27.3.1 Vectors Macro Attribute Descriptions​

AllAttributeswithinthisModulecontainingpointsorvectorsareencodedasmulti-valuedfloatsinanx-y-zordering.Ifmultipleelements​ are encoded, the ordering is x1,y1,z1,…,xn,yn,zn.​

The vectors encoded in this Macro can be anything from 1D to nD objects. The vectors are encoded as a stream of values in the​ Vector Coordinate Data (0066,0021) Attribute. Vector Dimensionality (0066,001F) defines how many subsequent entries in Vector​ Coordinate Data (0066,0021) describe one element. Vector Coordinate Data (0066,0021) shall have (Number of Vectors) x (Vector​ Dimensionality) values.​

For measured vectors, Vector Accuracy (0066,0020) describes the error per dimension in a multi-valued float Attribute.​

Note​

The vectors are located at the points specified by the table including this Macro.​

C.27.4 Surface Mesh Primitives Macro​

Table C.27-4 specifies the Attributes of the Surface Mesh Primitives Macro.​

Table C.27-4. Surface Mesh Primitives Macro Attributes​

See Section C.27.4.1.​

- Standard -​

C.27.4.1 Surface Mesh Primitives Macro Attribute Descriptions​

TheSurfaceMeshPrimitivesMacrouses32-bitlongintegerpointindicestoreferencethepointratherthanrepeatingpointcoordinates.​ All of the point coordinates used are specified within the Surface Points Sequence (0066,0011) of the same Surface Sequence​ (0066,0002) Item. Point indices are described in Section C.27.2.1.1.​

Note​

Inapreviousedition,otherAttributeswereusedthathadanOWVRandalimitationtonomorethan65535pointspersurface.​ These have been retired and replaced with new Attributes. See PS 3.3 2014a.​

A Surface Mesh shall contain one or more of the following primitive types:​

If the Surface Points Normals Sequence (0066,0012) is not present, the default normals can be derived from the Surface Mesh​ Primitives.​

For the Triangle Strip, Triangle Fan and Facet the Long Primitive Point Index List (0066,0040) the ordering of the point references​ implies the direction of the primitive's normal: The normal points in the direction from which the referenced points are specified in a​ counterclockwise order. For finite volumes this shall be the outward direction.​

For the Line primitive, the ordering of the point references defines a directed path, starting with the first point and ending with the last​ point referenced in each Long Primitive Point Index List (0066,0040).​

ForPrimitivesoftypeTriangleStriporTriangleFan,theorientationofthenormalsisgivenbytheorderofthepointsinthefirsttriangle.​

- Standard -​