Definition

For any level-of-detail related organization instance LRO, whether an <LOD Related Features> instance or an <LOD Related Geometry> instance,

1. The <Base LOD Data> instance for each branch of LRO shall match the class specified by LRO's lod_data_type field.

2. For each pair of branches, if the <Base LOD Data> instances overlap, neither shall be a subset of the other.

   2.1	For two <Distance LOD Data> instances, neither interval shall be contained within the other. Specifically,
   	2.1.1 The ranges may touch at their endpoints; that is, the minimum_range of one may equal the maximum_range of the other. 2.1.2 If the ranges overlap by more than one endpoint, each shall have at least one fade band, so that one is fading in while the other is fading out for the overlap range.
   2.2	For two <Volume LOD Data> instances,
   	2.2.1 If the two branches both have outside = SE_FALSE, neither volume may be contained within the other. 2.2.2 The volumes specified may be identical if the link objects specify different values for their outside fields, provided that LRO complies with <<Distinct Link Objects>>.

3. If LRO inherited a <Base LOD Data> instance C as a component, such that C matches its lod_data_type, LRO's link objects shall fall within the scope specified by C.

   3.1	If C is a <Distance LOD Data> instance and LRO is SE_LOD_DATA_TYP_DISTANCE, each link object specified by LRO shall specify a range within the region covered by C.
   3.2	If C is a <Volume LOD Data> instance and LRO is SE_LOD_DATA_TYP_VOLUME, each link object specified by LRO shall specify a volume lying within that of C.
   3.3	No other classes of C permit a matching LRO 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.

   3.1	If a hierarchy is visible only from viewing distance X to viewing distance Y, none of its components can be visible outside that range.
   3.2	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.
   3.3	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 <Distance LOD Data> and
   • "sphere with radius 5 metres centred at 0, 0, 0" for <Volume LOD Data>.

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

FAQs

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