Explanation/Reference:
SDO_LRS.PROJECT_PT returns the projection point of a specified point. The projection point is on the geometric segment.
Format
SDO_LRS.PROJECT_PT(
geom_segment IN SDO_GEOMETRY,
point IN SDO_GEOMETRY,
tolerance IN NUMBER DEFAULT 1.0e-8
[, offset OUT NUMBER]
) RETURN SDO_GEOMETRY;
Where Offset (shortest distance) from the point to the geometric segment.
If you specify the output parameter offset, the function stores the signed offset (shortest distance) from the point to the geometric segment.
The offset of a point along a geometric segment is the perpendicular distance between the point and the geometric segment. Offsets are positive if the points are on the left side along the segment direction and are negative if they are on the right side. Points are on a geometric segment if their offsets to the segment are zero.
References:
https://docs.oracle.com/database/121/SPATL/sdo_lrs-project_pt.htm#SPATL1171
https://docs.oracle.com/database/121/SPATL/terms-and-concepts.htm#SPATL744