Working with a Linear Dimension Object on a PCB in Altium Designer

Parent page: PCB Objects

A placed Linear Dimension.

Summary

A linear dimension is a group design object. It places dimensioning information on the current PCB layer, with respect to a linear distance. The dimension value is the distance between the start and end markers (reference points selected by the user) measured in the default units. The references may be objects (tracks, arcs, pads, vias, text, fills, polygons or components) or points in free space.

Availability

Linear dimension objects are available for placement in the PCB Editor only. Use one of the following methods to access a placement command:

• Choose Place » Dimension » Linear from the main menus.
• Click the  button on the Place Dimension drop-down () of the Utilities toolbar.

Placement

After launching the command, the cursor will change to a cross-hair and you will enter dimension placement mode. Placement is made by performing the following sequence of actions:

1. Position the cursor and click or press Enter to anchor the dimension start point (this is the first reference point).
2. Move the cursor and click or press Enter to anchor the dimension end point (this is the second reference point).
3. The text can now be initially positioned. Move the cursor and click or press Enter when the text is in the desired position, to complete dimension placement.
4. Continue placing further linear dimensions, or right-click or press Esc to exit placement mode.

Additional actions that can be performed during placement are:

• Press the + and - keys (on the numeric keypad) to cycle forward and backward through all visible layers in the design respectively – to change placement layer quickly.
• Press Spacebar to rotate the dimension anti-clockwise or Shift+Spacebar for clockwise rotation. Rotation is in accordance with the value for the Rotation Step, defined on the PCB Editor – General page of the Preferences dialog.
• Press the Tab key to access an associated properties dialog, from where properties for the dimension can be changed on-the-fly.

Graphical Editing

This method of editing allows you to select a placed linear dimension object directly in the workspace and change properties such as the position of its text and its reference points, graphically.

When a linear dimension object is selected, the following editing handles are available:

A selected Linear Dimension.

• Click & drag A or B to adjust the dimension text position and extension line length.
• Click & drag C or D to move the start or end reference points of the dimension.

If the linear dimension object is totally non-referenced (i.e. it is not attached to any reference design objects) click anywhere on it – away from editing handles – and drag to reposition it. While dragging, the linear dimension can be rotated (Spacebar/Shift+Spacebar) or mirrored (X or Y keys to mirror along the X-axis or Y-axis respectively).

Non-Graphical Editing...

The following methods of non-graphical editing are available:

Via an Associated Properties Dialog

Dialog page: Linear Dimension

This method of editing uses the following dialog to modify the properties of a linear dimension object.

The Linear Dimension dialog.

The Linear Dimension dialog can be accessed prior to entering placement mode, from the PCB Editor – Defaults page of the Preferences dialog. This allows the default properties for the linear dimension object to be changed, which will be applied when placing subsequent linear dimensions.

During placement, the dialog can be accessed by pressing the Tab key.

After placement, the dialog can be accessed in one of the following ways:

• Double-clicking on a placed linear dimension object.
• Placing the cursor over a linear dimension object, right-clicking and choosing Properties from the context menu.
• Using the Edit » Change command and clicking once over a placed linear dimension object.

Via the PCB Inspector Panel

Panel page: PCB Inspector, PCB Filter

The PCB Inspector panel enables the designer to interrogate and edit the properties of one or more design objects in the active document. Used in conjunction with appropriate filtering - by using the PCB Filter panel, or the Find Similar Objects dialog - the panel can be used to make changes to multiple objects of the same kind, from one convenient location.

Via the PCB List Panel

Panel page: PCB List, PCB Filter

The PCB List panel allows the designer to display design objects from one or more documents in tabular format, enabling quick inspection and modification of object attributes. Used in conjunction with appropriate filtering - by using the PCB Filter panel, or the Find Similar Objects dialog - it enables the display of just those objects falling under the scope of the active filter – allowing the designer to target and edit multiple design objects with greater accuracy and efficiency.

Tips

1. A linear dimension object can be moved in the following ways:
   1. Selecting both the dimension object and the object that is being dimensioned. The whole can be dragged to a new location as required.
   2. Selecting the object that is being dimensioned only. The dimension text will follow the object in its alignment plane only. The dimension extensions will expand/contract to keep the relationship between dimension and object being dimensioned.
   3. Selecting the dimension object only. It is important to note that the dimension cannot be moved on its own if it is referenced by a design object. To move the dimension only, it must first be detached from the objects it is dimensioning.
2. The dimension's value automatically updates as its start or end points are moved. Likewise, if the position of the object that either reference point of the dimension is anchored to is changed, the dimension will update and expand/contract to reflect this.
3. When the reference or references to which a dimension object is attached are deleted, a dialog will appear, asking whether the dimension should also be deleted. If the dimension is not deleted, it remains in the workspace, but non-referenced.
4. Linear dimensions are group objects consisting of text and track segments. They can be converted to their set of primitive objects by choosing Tools » Convert » Explode Dimension to Free Primitives from the main menus. Once exploded, a dimension object can no longer be manipulated as a group object.