Creating and Using Planes

All Planes are created and held within a Library structure, and are owned by a Planes Library (PLLB) element. The part of the Draft database hierarchy relating to Planes is shown in Figure 5:3 below.

Figure 5:3. Database Hierarchy - Plane Elements

To use a plane to produce a sectioned VIEW, you need to create a View Section (VSEC) element under a VIEW; VSEC attributes are:

• PLRF (Plane Reference) - the name of the plane to be used.

• IDLN - an Id List name for the section to operate on. If left undefined this will default to the World (that means, /*). This means that all elements in the VIEW’s Id List will be sectioned. A single Design item name can be used.

• PMOD - the mode in which the plane will be used to section the VIEW, that means, the side to be retained or discarded. The default is STANDARD, which is as the plane is set-up. REVERSE switches the side to be retained or discarded. OFF switches the plane off.

• CLMO (centreline mode) By default this is set to ON, which has no effect on functionality. If it is set to OFF then the section will not be applied to line elements of Piping Components. This allows you to remove Components and tubing by a section plane, but leave the centreline to show the path of the Branch. All other non-solid primitives are sectioned normally and are unaffected by the value of attribute CLMO.

• SMOD (a View attribute) - the section mode attribute, which defines how small parts of piping components and implied tube that are cut by the front and back sectioning planes will be treated. This attribute only affects piping components and implied tube in orthogonal, non-perspective Views.

  If SMOD is set to STANDARD (the default), all elements will be sectioned in the usual way. If SMOD is set to OMIT FRACtional PCOMponents, the following functionality will apply when the design graphics of the View are updated:

  • All piping components whose origins (P0) lie outside the front and back sectioning planes will be removed from the drawlist. All other piping components will be drawn completely, even if they are cut by one of the sectioning planes.

  • All lengths of implied tube that lie outside the front and back sectioning planes will be removed from the drawlist. In this case the test for lying outside the sectioning planes will be based on the vector Parrive -> Pleave, and not on the actual volume occupied by the length of tube. Lengths of tube that lie within or cross the front or back sectioning planes will be drawn completely.

    Where an IDList is defined by a set of piping components (for example, ADD /VALVE1 /VALVE2 /VALVE3) the functionality will not apply.

    The names of the items omitted can be output by the command

    SMODE MESSAGES ON

    but this will include all those piping components in the View’s IDList that fall outside the clipping box and would therefore not be drawn in any case.

Several VSEC elements can be used to produce as complex a section as you require, but the larger the number the slower the operation will be.

After setting up the VSEC it is just a matter of updating the design (with an UPDATE Design command), remembering that sectioning will only take place if the VIEW attribute VTYPE is set for Local, Global or Universal hidden line removal, or Modelled wireline.