I need some clarification on oracle sdo_gtype 4402. I understand that sdo_gtype is codded as DLTT. D: Dimension L : linear reference T T: TT identifies the geometry type. It's clear to me that first 4 indicated that the feature is 4-D. I am not sure about the second "4" and linear reference term. I need to create a spatial table using sdo_gtype 4402 that's why seeking some clarification on it.
By reading the documentation of Oracle 12c https://docs.oracle.com/database/121/SPATL/sdo_geometry-object-type.htm#SPATL490 GTYPE=4402 is a 4-dimensional geometry where the measure is given with the 4th coordinate. The geometry itself is a line.
The SDO_GTYPE value is 4 digits in the format DLTT, where:
D identifies the number of dimensions (2, 3, or 4)
L identifies the linear referencing measure dimension for a three-dimensional linear referencing system (LRS) geometry, that is, which dimension (3 or 4) contains the measure value. For a non-LRS geometry, or to accept the Spatial and Graph default of the last dimension as the measure for an LRS geometry, specify 0. For information about the linear referencing system (LRS), see Linear Referencing System.
TT identifies the geometry type (00 through 09, with 10 through 99 reserved for future use).
02: Geometry contains one line string that can contain straight or circular arc segments, or both. (LINE and CURVE are synonymous in this context.)
Typically these geometries are used for roads. X, Y, and Z coordinates define the road geometry and M as a fourth coordinate gives the distance from the start point of the line. Pipelines and cable networks are other use cases.
This type describes a 3D line with measures.
The first 4 indicates the number of values that describe each vertex: X, Y, Z, M
The second 4 indicates the position of the measure value (M) in this set of numbers (ordinates) - as the last one. It also confirms that the shape is a 3D shape with measures, as opposed to a 4002 shape, where the last number can be anything - X, Y, Z, T for example: we make no assumption as to the meaning of the last ordinate.
As explained in other answers, this is a “Linear Refetenced Segment” or “LRS”. Lines like that carry a measure information at each vertex. That measure typically represents the distance of each vertex from the start of the line. But it could also represent time: for example time on a flight route since a plane took off ...
Measures must be all either increasing or decreasing. They can begin with any value (not necessarily 0). They can be positive or negative.
Not all vertices need have a measure. A measure is mandatory for the first and last vertex only. For all others measures are optional. Any missing measure is automatically interpolated from existing neighboring measures.