Linear Dimension

Modified by Susan Riege on Aug 21, 2018

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 by clicking Home | Dimension | then selecting Linear from the drop-down list.

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:

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

When dimensioning an object, anchor points become available to you that highlight where the dimension can be attached. The point nearest the cursor will be the one used and where the dimension will attach if you proceed to click or press Enter.

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 counterclockwise 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.

While attributes can be modified during placement (Tab to bring up associated properties dialog), keep in mind that these will become the default settings for further placement.

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.

C and D allow for re-definable references. Once the dimension is detached from a reference object, it becomes non-referenced and can be moved for attachment to a different reference point or object. As you drag any of the editing handles, the dimension can be rotated.

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).

An object that has its Locked property enabled cannot be selected or graphically edited. Double-click on the locked object directly then disable the Locked property to graphically edit the object.

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 during placement by pressing the Tab key.

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

Double-click on the placed linear dimension object.
Place the cursor over the linear dimension object, right-click then choose Properties from the context menu.

Quickly change the units of measurement currently used in the dialog between metric (mm) and imperial (mil) using the Ctrl+Q shortcut. This affects the dialog only and does not change the actual measurement unit employed for the board as determined by the and buttons in the Home | Grids and Units area of the main menus.

Via the PCB Inspector Panel

Panel page: PCB Inspector

The PCB Inspector panel enables you to interrogate and edit the properties of one or more design objects in the active document. Used in conjunction with appropriate filtering, the panel can be used to make changes to multiple objects of the same kind, from one convenient location.

Notes

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.
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.
When the reference or references to which a dimension object is attached are deleted, a dialog will open asking whether the dimension should also be deleted. If the dimension is not deleted, it remains in the workspace, but non-referenced.

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