Database Elements for Underlays and Overlays

Elements for use as backing and overlay sheets can be created in DRAW and stored in the DRAW database. The relevant part of the database hierarchy is indicated.

The SHLB (Sheet Library) exists as a member of a LIBY and is used as an administrative element to group together BACK (Backing Sheet template) and OVER (Overlay Sheet template elements.

A BACK can be used as a frame sheet and can contain frame lines and authorisation boxes. These exist as (member) NOTE elements created via DRAW’s geometric 2D drafting facilities. Any hash codewords defined by TEXP elements are expanded when the BACK is referenced. These codewords typically extract data from the DRAW database. Refer to Access Data from the Draw Database for further information.

OVER elements can own NOTEs as well as VIEW elements, and can be used to overlay graphic details. For example, keyplans on drawing sheets. An OVER shares many of the attributes of a SHEE. Note that Point Construction (refer to Point and Line Construction for further information) can be used to create BACK and SHEE elements.

Most Overlay Sheet attributes are held by the Overlay (OLAY) element.

BACKs and OVERs are referred to by the relevant drawing Sheet’s BSRF and the relevant Overlay’s OSRF attributes (respectively). (BSRF can also be set at Drawing level.) The BACK/OVER to be used can be specified by using commands, for example:

The Overlay’s OSLV (‘overlay sheet view layers visible’) attribute defines those Layers of the overlay sheet (for example, the LAYE element(s) owned by the VIEW(s) owned by the OVER referenced by the drawing Sheet) that are to be visible.

The Overlay’s XYSCALE attribute allows independent scaling in the X and Y directions of the instanced overlay sheet or plotfile. For example:

XYSCALE 2 1

Either or both values can be negative, but zero is not allowed.

Note that when an Overlay Sheet is instanced (for example, attribute OSRF is set), text is only affected by the scale in the Y direction. It is not possible to generate backwards or distorted text. However, when a plotfile is used (for example, attribute OSFN is set), then there is no such safeguard and text can be distorted if differing X and Y scales are specified. Refer to Scale and Mirror Special Labels for further information.

Control of complex overlays can be achieved by using multiple OLAY elements.

The Layers which are to be visible can be referred to either by Layer purpose (for example, the PURP attribute) or by their member list position under the VIEW(s) owned by the OVER. Up to 12 Layers can be made visible at once. The Layers that are to be visible are specified by a further option of the OSHEET command. For example:

The Design graphics can be made visible by including Layer DESI. If the overlay sheet has more than one VIEW then the Layer visibility statement applies across all VIEWs. (It is not possible to specify, for example, a Layer with PURP DIMS to be visible for /VIEW1 but not for /VIEW2, assuming both VIEWs own such Layers.) The setting of a Layer’s LVIS attribute has no bearing on the visibility questions discussed in this section.

The functionality is only available when an overlay sheet template reference is used. No distinction between Layers can be made when using overlay sheet graphics from a file.