Oracle Spatial User's Guide and Reference - InfoLab

Figure 7–7 Creating a Geometric Segment
Indexing of LRS Data
In Figure 7–7, the geometric segment has the following definition (with measure
values underlined):
SDO_GEOMETRY(3302, NULL, NULL,
SDO_ELEM_INFO_ARRAY(1,2,1),
SDO_ORDINATE_ARRAY(5,10,0, 20,5,NULL, 35,10,NULL, 55,10,100))
Whenever a geometric segment is defined, its start and end measures must be
defined or derived from some existing geometric segment. The unsigned measures
of all shape points on a geometric segment will be automatically populated.
The LRS API works with geometries in formats of Oracle Spatial before release
8.1.6, but the resulting geometries will be converted to the Oracle Spatial release
8.1.6 or higher format, specifically with 4-digit SDO_GTYPE and SDO_ETYPE
values. For example, in Oracle Spatial release 8.1.6 and higher, the geometry type
(SDO_GTYPE) of a spatial object includes the number of dimensions of the object as
the first digit of the SDO_GTYPE value. Thus, the SDO_GTYPE value of a point is 1
in the pre-release 8.1.6 format but 2001 in the release 8.1.6 format (the number of
dimensions of the point is 2). However, an LRS point (which includes measure
information) has three dimensions, and thus the SDO_GTYPE of any point
geometry used with an LRS function must be 3301.
7.3 Indexing of LRS Data
Start Measure
(5, 10, 0) (35, 10, NULL)
End Measure
(55, 10, 100)
Start Point End Point
(20, 5, NULL)
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, and you must specify PARAMETERS('sdo_indx_dims=3') in the
CREATE INDEX statement to ensure that the first three dimensions are indexed.
Note, however, that if you specify an sdo_indx_dims value of 3 or higher, the
only Spatial operator that can be used on the indexed geometries is SDO_FILTER;
the other operators described in Chapter 12 cannot be used. (The default value for
the sdo_indx_dims keyword is 2, which would cause only the first two
dimensions to be indexed.) For example, if the dimensions are X, Y, Z, and M,
specify sdo_indx_dims=3 to index the X, Y, and Z dimensions, but not the measure
Linear Referencing System 7-9