7 Linear Referencing System

Linear referencing is a natural and convenient means to associate attributes or events to locations or portions of a linear feature. It has been widely used in transportation applications (such as for highways, railroads, and transit routes) and utilities applications (such as for gas and oil pipelines).

The major advantage of linear referencing is its capability of locating attributes and events along a linear feature with only one parameter (usually known as measure) instead of two (such as longitude/latitude or x/y in Cartesian space). Sections of a linear feature can be referenced and created dynamically by indicating the start and end locations along the feature without explicitly storing them.

The linear referencing system (LRS) application programming interface (API) in Oracle Spatial provides server-side LRS capabilities at the cartographic level. The linear measure information is directly integrated into the Oracle Spatial geometry structure. The Oracle Spatial LRS API provides support for dynamic segmentation, and it serves as a groundwork for third-party or middle-tier application development for virtually any linear referencing methods and models in any coordinate system.

For an example of LRS, see Example of LRS Functions. However, you may want to read the rest of this chapter first, to understand the concepts that the example illustrates.

For reference information about LRS functions and procedures, see SDO_LRS Package (Linear Referencing System) .

• LRS Terms and Concepts
  This topic explains important terms and concepts related to linear referencing support in Oracle Spatial.
• LRS Data Model
  The Oracle Spatial LRS data model incorporates measure information into its geometry representation at the point level.
• Indexing of LRS Data
  If LRS data has four dimensions (three plus the M dimension) and if you need to index all three non-measure dimensions, you must use a spatial R-tree index to index the data.
• 3D Formats of LRS Functions
  Most LRS functions have formats that end in _3D: for example, DEFINE_GEOM_SEGMENT_3D, CLIP_GEOM_SEGMENT_3D, FIND_MEASURE_3D, and LOCATE_PT_3D. If a function has a 3D format, it is identified in the Usage Notes for the function’s reference topic.
• LRS Operations
  This topic describes several linear referencing operations supported by the Oracle Spatial LRS API.
• Tolerance Values with LRS Functions
  Many LRS functions require that you specify a tolerance value or one or more dimensional arrays.
• Example of LRS Functions
  This section presents a simplified example that uses LRS functions.