Understanding linear referencing and measures

All geographic representations stored in the SDO_GEOMETRY object are just that: representations. The linestring describing a pipe is not the pipe; the linestring describing a road in a GPS in-car navigation unit is not the road: they are scale-dependent representations of the middle of the pipe (an imaginary line drawn down the center of the pipe) or the middle of a marked lane for traffic on a road.

By scale-dependent is meant that the position of each vertex in the linestring has a locational "vagueness". The amount of location vagueness depends on the source of its measurement. A position measured by a surveyor using a modern electronic theodolite may be accurate to +/- 5mm; a GPS observation +/- 10cm; an old 1:1000 map from a roads department, +/- 2m.

Regardless as to capture method, each linestring's representation has an implicit length (measured by SDO_GEOM.Sdo_Length or the T_GEOMETRY.ST_Length method) property, but this length is also...