Definition

For any level-of-detail related organization instance L, whether an instance of <LOD Related Features> or <LOD Related Geometry>, the following apply:

1. The <Base LOD Data> link object for each branch of L shall match the class specified by L's lod_data_type field value.

2. For each pair of branches with <Distance LOD Data> or <Volume LOD Data> link objects that overlap, neither shall be a subset of the other, as follows:

   1. For <Distance LOD Data> link objects, neither interval shall be contained within the other. Specifically,

      1. The ranges may touch at their endpoints; that is, the minimum_range field value of one may equal the maximum_range field value of the other.

      2. If the ranges overlap by more than one endpoint, each <Distance LOD Data> link object shall specify at least one fade band, so that one branch is fading in while the other is fading out for the overlap range.

   2. For <Volume LOD Data> link objects,

      1. If the two branches both have outside = SE_FALSE, neither volume may be contained within the other.

      2. The volumes specified may be identical if the link objects specify different values for their outside fields, provided that L complies with the constraint specified in <<Distinct Link Objects>>.

3. If L inherits a <Base LOD Data> instance C as a component, such that C matches L's lod_data_type field value, the link objects of L shall fall within the scope specified by C:

   1. If C is a <Distance LOD Data> instance and L has an lod_data_type field value of SE_LODDATTYP_DISTANCE, each link object specified by L shall specify a range within the region covered by C.

   2. If C is a <Volume LOD Data> instance and L has an lod_data_type field value of SE_LODDATTYP_VOLUME, each link object specified by L shall specify a volume lying within that of C.

   3. No other classes of C permit a matching L to occur in their inheritance tree.

Rationale

1. The mechanism for switching between different levels of detail is defined only if the "type" of level of detail is homogeneous.

2. Different branches of a level-of-detail related organization can be active at the same time only if one is incoming and the other is outgoing.

3. The component tree of an item with level-of-detail information shall comply with that level-of-detail.

   1. If a hierarchy is visible only from viewing distance X to viewing distance Y, none of its components can be visible outside that range.

   2. If a hierarchy is visible only inside (or outside) a given viewing volume, all of its components are also inside (or outside) the given viewing volume.

   3. If a hierarchy is visible only at a specific index, map scale, or spatial resolution, none of its components can be visible at any conflicting value.

Example

1. It isn't defined for a data provider to switch between

   • "0-500 metres" for a <Distance LOD Data> instance and
   • "sphere with radius 5 metres centred at 0, 0, 0" for a <Volume LOD Data> instance.

2. Range-based components and index-based components will not be attached to the same <LOD Related Geometry> instance.

FAQs

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