Positioning Items Relative to Generic Sections

A GENSEC cannot own Fixings directly, but only via member Justification Line Datum and P-line Datum elements which together define the p-line configurations to be used as references for positioning and orientating the Fixings.

The Justification Line Datum (JLDATUM) element defines a frame of reference for its members based on the p-line system of its owning GENSEC. Each JLDATUM can own a set of P-line Datum (PLDATUM) elements, each of which defines a frame of reference for its members based on a nominated p-line of its owning JLDATUM. By manipulating a JLDATUM, all of its member PLDATUMs can be manipulated as a group, together with any Fixings owned by the latter.

Note:
The JLDATUM and PLDATUM elements together serve similar functions to the Secondary Nodes (SNOD) used for positioning Fittings (FITT), Compound Fittings (CMFI), Secondary Joints (SJOI) and Compound Secondary Joints (SCOJ) relative to Sections (SCTN). They also provide similar functions to those used for positioning Panel Fittings (PFIT) and Compound Panel Fittings (CMPF), depending on the GENSEC configuration (remember that a GENSEC can model a wide range of geometries, including structural sections and panels).

Specifying Position

The position of a JLDATUM origin may be queried via a pseudo-attribute (Q POS), but this cannot be set explicitly. The position is derived from the following attribute settings:

• TPREF and HPREF specify, by reference to POINSPs of the parent GENSEC (more strictly, its Spine), the start and end points, respectively, between which interpolated positions will be calculated. If both are unset, TPREF defaults to start of the GENSEC and HPREF defaults to the end of the GENSEC. If only one is set, the other defaults to the next POINSP in the appropriate direction.

• PKDI specifies a point, as a proportion of the distance from TPREF to HPREF, from which ZDIST is to be measured. The default setting is 0, giving a position at TPREF. If PKDI is less than 0 or greater than 1, the position will be on the preceding or following segment, respectively, of the Spine.

• ZDIST specifies the distance of the JLDATUM origin from the PKDI point, as measured along the Justification Line (JUSL) or NA p-line of the GENSEC.

Specifying Orientation

The orientation of a JLDATUM may be queried via a pseudo-attribute (Q ORI), but this cannot be set explicitly. The orientation is such that its Z axis is in the direction of the Spine (i.e. the NA p-line) at the POS. The Y axis is in the Y direction (YDIR) of the Spine, modified by the Beta Angle (BANG) setting, at the POS.