Showing Dimensions on Template Designs

The Design Templates application incorporates a facility for creating pairs of Dimension Points (actually spherical design points; see Adding Design Points), for use as datum points for displaying design template dimensions. Each dimension point can have its position and associated projection line defined by a set of rules.

If you are dimensioning a new template, where no dimension point rules have yet been defined, an ‘autobuild’ function can be used to create pairs of dimension points automatically for all design parameters.

The dimensions which we will add to our equipment template, based on the design parameters specified in Steps 1 through 4 of Restricting Property Values for use in a Design , are as follows (the numbers will be explained in the next steps):

While each dimension point position and projection line extension could be defined explicitly, this could lead to an inappropriate display if, say, the vessel were made large enough to obscure them. It is best, therefore, to specify the positions and extensions in terms of rules based on the design parameter values. The dimensioning annotations are then scaled automatically as the vessel dimensions are modified.

Exercise continues:

1. With /Vessel-Main-Body as the current element, select Create > Dimension Points. You will see a Dimension Point Definition form which lets you specify the position (Dimension Position), extension line length (Dimension Extension) and extension line direction (Dimension Direction) for each dimension point in each pair.

   From the Dimension Point Definition form’s menu bar, select Control > AutoBuild. This will create two dimension points for each of the four design parameters, as shown in the Dimension Points list, thus:

   

   The points are numbered in pairs (as shown in the preceding diagram), and are given descriptions which include the design parameter DKEYs; for example, points 101 and 102 form a pair which will show the DIAM dimension.

   When first created, all dimension points are positioned at the template origin (shown by the sphere in the 3D View). What we now have to do is reposition each point and specify its projection line length and direction.

2. Select point 101. Leave the Design Point Description, Design Param No. and Dpoint No. settings as they are (we will not change these for any of the points).

   Click next to the Dimension Position field to display the Position Rule Definition ‘expression builder’ form. Build up the following expression and compare it with the design parameter definitions to ensure that you understand why it gives a suitable position for this point:

   N (CDPR LENG / 2) U (CDPR CHEI ‑ CDPR DIAM / 2)

   (The expression builder may insert extra spaces and pairs of parentheses, but these are not essential.) The N (north) displacement, by half the length of the vessel body, should be sufficient to position the dimension point clear of the vessel’s end in the completed design.

   Set the Dimension Extension to (CDPR LENG / 2) and the Dimension Direction to S (south), so that the projection line from this point is directed towards, and just reaches, the end of the vessel body.

   Click the Replace button to overwrite the data for point 101 with you new settings. The effect is as follows:

   

3. Select point 102. This will differ from point 101 only in its U (up) coordinate, so, to save entering all the data again, click the Copy Partner button. This button copies all position and projection line settings from the other point in a pair; for example, from 201 to 202 or from 202 to 201.

   Edit the Dimension Position rule by changing the ‑ sign to a + sign, thus:

   N (CDPR LENG / 2) U (CDPR CHEI + CDPR DIAM / 2)

   and click Replace. The result should be:

   

4. We will set the Thickness dimension points next, since these will use some of the data from the Diameter points. (It is sensible to think about the order in which you edit dimension points, so that you minimize the amount of editing required.)

5. Select point 301. The data for this point will be derived from the settings for point 102, so click the Copy Last Point button. This button copies all position and projection line settings from the point which was selected prior to the current point (which in this case was point 102).

6. We will position point 301 midway between point 102 and the end of the vessel body, so edit the rules thus:

   Dimension Position	N (CDPR LENG / 4) U (CDPR CHEI + CDPR DIAM / 2 )
   Dimension Extension	(CDPR LENG / 4)
   Dimension Direction	S

   and Replace.

7. Set the rules for point 302 by using the Copy Partner facility.

   The only rule change needed is to reduce the U(up) co-ordinate by the vessel’s wall thickness, thus:

   Dimension Position

   ... U (CDPR CHEI + CDPR DIAM / 2 ‑ CDPR THKN)

8. We will next set the rules for the Centreline Height dimension points, positioning these at the opposite end of the vessel from the previous points for clarity.

   Set the rules for point 401 as follows:

   Dimension Position	S (CDPR LENG * 1.5)
   Dimension Extension	(CDPR LENG * 1.5)
   Dimension Direction	N

   Set the rules for point 402, using Copy Partner, thus:

   Dimension Position	S (CDPR LENG * 1.5) U (CDPR CHEI)
   Dimension Extension	(CDPR LENG * 0.5)
   Dimension Direction	N

9. Finally, we will set the rules for the Length dimension points. We will position these points relative to the locally-named design points at the centers of the vessel body end faces.

   Set the rules for point 201 thus:

   Dimension Position	U (CDPR DIAM * 2) from LNID /Datum-Point-1 (use the expression builder’s Local Names feature)
   Dimension Extension	(CDPR DIAM * 1.5)
   Dimension Direction	D

   Set the rules for point 202 thus:

   Dimension Position	U (CDPR DIAM * 2) from LNID /Datum-Point-2
   Dimension Extension	(CDPR DIAM * 1.5)
   Dimension Direction	D

   When you are satisfied that all of the dimensioning rules are correct, select Control > Close to dismiss the Dimension Point Definition form.