Angular Dimensions and How to Create Them

This section concentrates on those features that are unique to Angular Dimensions.

The simplest type of Angular Dimension (ADIM) consists of a pair of directions in the Design model (the dimension directions) that radiate out from the dimension origin. These directions are projected onto the drawing and are represented by projection lines. Between these lines a dimension arc is drawn centered upon the dimension origin. Each dimension arc and projection line may have a piece of text associated with it.

The dimension origin may either be defined explicitly by attributes of the ADIM or implicitly by the intersection of two dimension directions. These are illustrated by Figures 12:32 and 12:33 below.

Figure 12:32. Single Value Angular Dimension with origin defined in database

Figure 12:32 above shows an Angular Dimension with its origin defined as a Nozzle in the center of the vessel. The two dimension directions are both defined as directions from the ADIM's origin to the origins of Nozzles. This Angular Dimension could be created by typing the following commands, starting at Layer level:

Having pressed Enter when the confirmation command line appears, the Dimension will appear on the display. A pair of Dimension Direction elements will have been created, with the last direction becoming the current element.

In this example the ID @ commands could all be replaced by IDP @. This would allow p-points to be nominated instead of Design items.

The ON command sets the DDNM attribute of the ADIM to the name of the Design element at the Dimension origin. The NPPT attribute of the ADIM is set to the nominated p-point. If none is defined (as in this example) NPPT will be set to a default value that equates to the origin of the element named by the DDNM.

In this example the Dimension Directions will be DPPT elements: these also have DDNM and NPPT attributes. In this case DDNM is set to the name of the Design element specified by the FROM or TO keyword, and NPPT to the nominated p-point (or the origin by default).

The DPOS @ command, which allows the position of the Dimension Arc to be defined, sets the DPOS attribute of the Angular Dimension. Alternatively the Arc radius could be defined by setting the Dimension's DOFF attribute. For convenience both these attributes can be set at members of the Angular Dimension. They are mutually exclusive: setting one will cause the other to be unset.

For the Angular Dimension shown in Figure 12:33 the Q DESCription command will typically give:

On /C1101-N6

Dimension points

1 DPPT From /C1101-N1

2 DPPT To /C1101-N10

Figure 12:33. Single Value Angular Dimension with origin defined by intersection

Figure 12:33 above shows an Angular Dimension with its origin defined implicitly by the intersection of the two Dimension directions, which are plines of SCTNs.. This Angular Dimension could be created by typing the following commands, starting at Layer level:

Having pressed Enter when the confirmation command line appears, the Dimension will appear on the display. The position of the Dimension's origin will have been automatically calculated from the intersection of the two Dimension Directions. A pair of Dimension Direction elements will have been created, with the last direction becoming the current element.

In this example the DIR IDPL @ commands could be replaced by either of:

• DIR IDP @ in which case the nominated p-points will be used to define directions;

• DIR ID SCTN @ in which case the NA pline of the nominated SCTN will be used.

In this example the DDNM and NPPT attributes of the ADIM are left unset. The Dimension Directions will be APPT elements: these have DDNM, PPDI, and PKEY attributes. In this case DDNM is set to the name of the Design element specified by the FROM or TO keyword, and PPDI or PKEY to the nominated p-point or pline as appropriate. PPDI and PKEY are mutually exclusive: setting one will cause the other to be unset.

Plines and p-points define specific directions (eg UP) but in some cases when defining Angular Dimensions it is the 'reversed' direction that is required (eg DOWN). This can be achieved by the use of the REVDIR attribute of APPTs. By default this is False (or OFF) and the direction of the specified pline or p-point will not be reversed when drawing the Angular Dimension. If the reversed direction is required it should be set True (or ON).

When using two intersecting APPTs to define an Angular Dimension there are four possible quadrants in which the Dimension Arc will be drawn. All four possibilities can be obtained by setting the two REVDIR attributes appropriately. However the required result can be achieved automatically by setting the DPOS attribute. From the DPOS coordinates DRAFT will calculate and set the REVDIR attributes of the two APPTs.

For the Angular Dimension shown in Figure 12:33 above, the Q DESCription command will typically give:

Position unset

Dimension points

1 APPT From Direction Ppline NA of /F-2

2 APPT To Direction Ppline MEML of /F2-BRAC-1 Reversed

Note: The direction of the second APPT has been reversed by the action of the DPOS @ command so that the Dimension Arc is drawn in the required quadrant.

The other types of Dimension Direction that may be owned by an ADIM element are:

• DPOI allows the direction to be defined by any given 3D position

• ADIR allows the direction to be defined by any given 3D direction

DPOI elements would be created by a sequence such as:

NEW ADIM

ON ID @

FR POS @ TO POS @

Here the FROM and TO commands set the POS attribute of each DPOI to the position defined by the cursor.

ADIR elements would be created by a sequence such as:

NEW ADIM

ON ID @

FR DIR N30E TO DIR S20W

The DIR attribute of each ADIR will be set to the specified direction.

In each example above, the FROM keyword defines the Direction at the start of the Dimension's member list, TO defines a Direction after the last item in the list. The Directions will be drawn in the order in which they appear in the list, and the rotational direction between the Directions is determined by the minor arc between the first two Directions.

The above examples show the easiest way of creating ADIM elements, but many other methods are available. The dimension origin can be defined explicitly as a 3D point, as a p-point, as a proportional distance along a pline, as a Branch Head or Tail, or as (the origin of) any Design element.

An example of a multi-valued chained Angular Dimension is shown in Figure 12:34 below.

Figure 12:34. Chained Angular Dimension

Such a dimension is created in a similar way to a chained Linear Dimension. Notice how the Dimension Arc text is (automatically) oriented and positioned relative to the Dimension Arc so as to make it easiest to read.

In this example the PLTX attribute of the ADIM is set to '#DIMDIR' and as a result the dimension directions appear as projection line text. #DIMDIR is an example of an intelligent text codeword - see Intelligent Text. #DIMDIR is valid in the PLTX of ADIM elements and their four potential member types.

For the Angular Dimension shown in Figure 12:34 the Q DESCription command will typically give:

On P 0 of /C1101-N6

Dimension points

1 DPPT From /C1101-N1

2 DPPT To P 0 of /C1101-N8

3 ADIR To E

4 DPPT To /C1101-N10

5 DPPT To P 0 of /C1101-N12

Additional 'links' can be inserted in or added to a chained Dimension (or a single-valued Dimension can be 'converted' to a chained Dimension) by using the INSERT command in a similar way to Linear Dimensions.

The SORT DIM command can also be used with Angular Dimensions to reorder any incorrectly ordered Directions.

An example of a parallel Angular Dimension is shown in Figure 12:35 below.

Figure 12:35. Parallel Angular Dimension

A parallel Dimension can be produced simply by setting the LCHA attribute of an ADIM to False (a chained dimension has LCHA True).