線形寸法

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.
• Locate and use the Linear command () on the Active Bar.  

• Click the  button on the Place Dimension drop-down () of the Utilities toolbar.
• Right-click in the workspace then choose the Place » Dimension » Linear command from the context menu.

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 then click or press Enter to anchor the dimension start point (this is the first reference point).
2. Move the cursor then 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 then 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 to change placement layer quickly. Alternatively, use the Ctrl+Wheelroll shortcut to cycle through the available layers.
• Press Spacebar to toggle the dimensioning direction between horizontal and vertical.

Graphical Editing

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

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.

1. A dimension object can be moved in the following ways:
   1. Selecting both the dimension object and the objects that are being dimensioned. The whole can be dragged to a new location as required.
   2. Selecting an 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 an object that a reference point of the dimension is anchored to is changed, the dimension will update and expand/contract to reflect this.
3. If the 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 then drag to reposition it. While dragging, the dimension can be rotated or mirrored:
   1. Press the 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.
   2. Press the X or Y keys to mirror the dimension along the X-axis or Y-axis respectively.

Non-Graphical Editing

The following methods of non-graphical editing are available:

Editing via the Properties Panel

Properties page: Linear Dimension Properties

The properties of a Linear Dimension can be edited in the PCB editor's Properties panel, which allows editing of all item(s) currently selected in the workspace.

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

To access the properties of a placed Linear Dimension:

• Double-click on the Linear Dimension.
• Right-click on the Linear Dimension then select Properties from the context menu.

If the Properties panel is already active:

• Click once on the Linear Dimension to select it, and access its properties in the panel.

Editing via the PCB List Panel

Panel page: PCB List, PCB Filter

The PCB List panel allows you 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 you to target and edit multiple design objects with greater accuracy and efficiency.

Tips

1. 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.
2. 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.