The SEDRIS Data Representation Model
APPENDIX B - Constraints
Linear Geometry Structure

Definition

For a <Linear Geometry> instance G, the following conditions shall hold.

  1. Each <Vertex> component of G shall appear exactly once as a component of G.

  2. No two <Vertex> components of G shall occupy the same position in space.

  3. If G is an <Arc> instance, the <Location> component of G shall not occupy the same position in space as any of the <Vertex> components of G.

  4. Let L be a <Linear Geometry> instance that is associated with n ordered <Geometry Edge> instances E1, ..., En through the use of n <Edge Direction> link objects D1, ..., Dn, where n ≥ 1.

    1. If D1 has a forwards field value of SE_TRUE, the start <Geometry Node> instance of E1 shall be associated with the first <Vertex> component of L. Otherwise, the end <Geometry Node> instance of E1 shall be associated with the first <Vertex> component of L.

    2. If Dn has a forwards field value of SE_TRUE, the end <Geometry Node> instance of En shall be associated with the last <Vertex> component of L. Otherwise, the start <Geometry Node> instance of En shall be associated with the last <Vertex> component of L.

    3. If n > 1, for each Ei, Ei+1, where i = 1, ..., n-1, Ei and Ei+1 shall associate to a common <Geometry Node> instance. For each consecutive <Geometry Edge> instance Ei within the sequence, Di shall be consistent with the starting and ending nodes of the edge.

      1. Consider the case where L is a <Line> instance. L shall have exactly n+1 <Vertex> components Vi, each of which has an associated <Geometry Node> instance Gi, which shall be the common <Geometry Node> instance for Ei and Ei+1.

      2. Consider the case where L is an <Arc> instance expressed by a sequence of edges.The <Geometry Node> instances forming the ends of the edges shall all be intersected by the circle for which the <Arc> instance is specifying a subsection.

Rationale

The <Location> information of a <Linear Geometry> instance is required to be distinct in order to form geometrically valid <Linear Geometry> instance.

Example

  1. An <Arc> instance, in order to specify a geometric arc, is required to have distinct endpoints, and the <Location> instance about which it is symmetric is required to be distinct from those endpoints for the same reason.

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