The PCB Editor is a grid-based design environment - design objects are placed on what is referred to as the placement, or snap grid. Multiple snap grids can be defined, and these can be restricted to a specified area if required. Snap grids are prioritized, with the highest priority grid available at the current location, being applied automatically. Snap grids can also be restricted to Components, or Non Components.
As well as the snap grid, the software includes a number of additional snap features, designed to help you accurately position and align design objects. Together, these features are referred to as the Unified Cursor-Snap System. 'Cursor-snap' is the process whereby the physical mouse cursor's pixel position on the screen drives the position of a 'logical cursor' in the coordinate space of a design document such as a PCB. The objective is for the system to be able to place the logical cursor onto sensible and useful coordinates without the user needing to specify these in a high resolution way. Variable geometry boards - where component pins are often placed on quite different metric and imperial grids - serve to add greater complexity to this objective.
The system brings together different sub-systems to collectively drive the way that the cursor snaps onto given sets of preferred coordinates:
- User-Definable Grids - available in both Cartesian and Polar formats.
- Snap Guides - that can be freely placed and provide a handy visual cue for object alignment.
- Object Snapping - enabling placed objects to pull the cursor into position, based on cursor proximity to that object's snap points (hotspots).
- Axis Snapping - a feature to pull the cursor, in either the X or Y direction, so that it axially-aligns with an object's hotspot.
These features combine to ensure streamlined placement and alignment of objects in the PCB workspace.
Accessing the Unified Cursor-Snap System
The Unified Cursor-Snap System is configured in the Properties panel (accessed when there are no design objects currently selected in the design workspace). The images below show the sections of the panel that are used to configure the unified cursor-snap system.
Access controls for the Unified Cursor-Snap System in the Properties panel, including the Snap Options, Grid Manager and Guide Manager.
The following three sections of the panel are used to configure:
- Snap Options - providing options to determine cursor snapping (first image):
- Grids - used to toggle whether the cursor will snap to the active workspace grid. When this option is enabled the cursor will pull, or snap, to the nearest snap grid location. The active snap grid is displayed on the Status bar, and in the PCB editor Heads Up display (Shift+H to toggle on/off).
- Guides - used to toggle whether the cursor will snap to manually placed linear or point Snap Guides. A Snap Guide will override the Snap Grid.
- Axes - used to toggle whether the cursor will axially-align (in either the X or Y direction) to the enabled Objects for snapping. The Axis Snap Range defines the distance within which X or Y axial-alignment will occur. A dynamic alignment guide line is displayed when alignment is achieved, from the current cursor location to the axially-aligned object snap point (hotspot).
- Snapping - used to control whether object snapping is Off, if object snapping only occurs to the enabled objects on the Current Layer, or if object snapping occurs to the enabled objects on All Layers.
- Object for snapping - object snap points (hotspots) that will be snapped to during an edit action, such as placement or movement.
- Snap Distance - when the cursor is within this distance from an enabled object snap point (and snapping is enabled for the active layer), the cursor will snap to that point.
- Axis Snap Range - when the cursor is axially-aligned and within this distance from an enabled object snap point (and the Axes feature is enabled), a dynamic guide line will display to indicate that alignment has been achieved.
- Grid Manager - where local customized grids can be defined and managed, as well as the default Snap Grid for the board. (second image)
- Guide Manager - where a range of manual Snap Guides and Snap Points for the board can be defined and managed. (third image)
Understanding the Snap Behavior
The PCB editor workspace is a high-precision design environment containing objects that are designed to different scales, sometimes using different units of measurement. The unified cursor-snap system simplifies the process of working in such a complex design space, providing multiple levels of cursor snapping during object placement or movement.
The Snap Points
There are three levels of cursor-snapping available, each level overrides the lower level(s):
- Grid - the active Grid provide the base-level reference plane for snapping. The logical, or editing cursor, snaps from one grid point to the next as you move the mouse cursor across the screen.
- Snap Guides - overlaying this plane of grid points, snap Guides provide a method of defining precise, localized reference lines or points.
- Objects - the third, and often the most useful points of reference for snapping, are the objects that have already been placed in the workspace. Using the checkboxes in the Objects for snapping list, specific points on each object-type can be enabled as snap points, which are also referred to as object hotspots.
The Snap Strength
The strength of the snap is defined by the Snap Distance. When the mouse cursor moves within this distance from an enabled Object for snapping, the editing cursor immediately snaps to that object's hotspot. Reduce this value to weaken the snap strength, increase the value to strengthen the snap effect. Keep in mind that a large value for the Snap Distance may prevent you from positioning the cursor at certain grid locations, whenever a nearby object's hotspot is within the Snap Distance.
Interactively Controlling the Snap Behavior
As you can see in the video above, a key feature of working with the snap options is being able to reconfigure them as you work. At any time you can press Ctrl+E to display a palette of snap options.
Snap Options shortcuts:
- Ctrl+E - display a palette of snap options
- Shift+E - cycle to the next Snapping mode (Off, Current Layer, All Layers)
- Ctrl - hold to temporarily inhibit object snapping
It is often impossible or impractical to define a grid that all design objects fall on to. In that situation you might need to position a new design object at an off-grid location. The software supports this through a feature called Object Snap, which is essentially a range of attraction around that object's hotspot. Hotspots only exist at meaningful locations, such as the center of a pad or via, and the end points of track segments.
This is a dual-axis system, where the mouse cursor must within the Snap Distance on both the X and Y axes, in order for the object to pull the cursor towards that hotspot. Object hotspot snapping provides an aid to routing electrical objects, especially those which may not fall on the active snap grid. The Snap Distance is configured in the Properties panel, when there are no objects selected in the workspace.
Off-grid objects can be snapped to, using the object hotspot snapping feature.
The Objects for snapping feature has three modes, use the buttons in the Snapping section of the Properties panel to select the required mode, or use the Shift+E keyboard shortcut to cycle through the modes as you work:
- Current Layer - hotspot snap is enabled for the current layer. That is, the cursor will snap to object hotspots on the current layer only. This mode is reflected on the Status Bar as (Hotspot Snap).
- All Layers - hotspot snap is enabled for all visible layers. That is, the cursor will snap to object hotspots on any layer, not just the current layer. This mode is reflected on the Status Bar as (Hotspot Snap (All Layers)).
- Off - hotspot snapping is disabled. The Status Bar displays nothing about Hotspot snap in this mode.
Aligning the Editing Cursor with a Placed Object
A common design task is to align a new object with an existing object. This can be achieved by enabling the Axes feature. When this feature is enabled, a dynamic alignment guide line is displayed from the current cursor location to the X or Y aligned object's hotspot, whenever the editing cursor is within the Axis Snap Range. This allows an object hotspot that is close to the mouse cursor on one axis, but distant on the other axis, to drive the cursor position.
With the axial alignment feature dynamic alignment guides appear in the workspace, from the cursor to the hotspots
of existing placed objects.
Any number of user-defined grids can be configured for the workspace, with all grid management performed from within the Grid Manager section of the Properties panel (accessed when there are no design objects currently selected in the design workspace). Use the controls available to define custom local grids by which to place design objects - especially components - with greater precision.
The Grid Manager section of the Properties panel - command central for defining and organizing the
grids for use with your board.
The software supports the creation of the following two custom grid types:
- Cartesian Grid - create a new grid of this type using the Add Cartesian Grid command (available from the button). A new grid entry will appear in the list, initially with the default name New Cartesian Grid. To edit the grid, simply double-click on its entry, or select its entry and click the button. The Cartesian Grid Editor dialog will appear, presenting options with which to define the grid.
Example Cartesian grid definition, using the Cartesian Grid Editor dialog, and resulting appearance in the workspace.
- Polar Grid - create a new grid of this type using the Add Polar Grid command (available from the button). A new grid entry will appear in the list, initially with the default name New Polar Grid. To edit the grid, double-click on its entry, or select its entry and click the button. The Polar Grid Editor dialog will appear presenting options with which to define the grid.
Example Polar grid definition, using the Polar Grid Editor dialog, and resulting appearance in the workspace.
Default Snap Grid
A default snap grid is defined for the board, named
Global Board Snap Grid. This is the grid that is used for object placement and movement in any area of the board not covered by a dedicated local grid.
Global Board Snap Grid - used in any area of the board where a custom local grid has not been defined.
The default grid is a Cartesian-type grid. The step size and/or display for the grid can be modified, but the grid cannot be renamed, disabled, or deleted.
Within the workspace, the G keyboard shortcut gives you access to a menu of commands for quickly setting the X (horizontal) and/or Y (vertical) step values for the default Global Board Snap Grid. These commands only affect the default snap grid for the board, and not any custom grids (Cartesian and polar) that you may have defined. Commands are available to quickly switch to another predefined step sizing, or to access the Snap Grid (1..1000) dialog, with which you can define a specific, custom sizing. Application of the predefined/custom value depends on whether you are setting both X and Y step values simultaneously, or X or Y step values individually:
- Setting X and Y step values simultaneously - if the Step X and Step Y properties of the Global Board Snap Grid were previously unlinked, this command will link the two, with both set to the same predefined/custom value.
- Setting X or Y step values individually - if the Step X and Step Y properties of the Global Board Snap Grid were previously linked, this type of command will unlink the two, with only the chosen (X or Y) step value set to the predefined/custom value. The other step value will remain at its previous setting.
The current snap grid setting - for the grid (default or custom local) currently under the cursor - is always displayed on the Status Bar, along with the cursor location, relative to the Current Origin. The current origin is user-definable and can be located anywhere in the workspace, the Absolute Origin is the bottom-left of the 100 x 100 inch workspace.
The Status Bar always displays the current snap grid and the cursor location
relative to the Current Origin.
The Status Bar also reflects the current state of object Hotspot Snapping. Object hotspot snapping provides an aid to routing electrical objects, especially those which may not fall on the default Global Board Snap Grid, or a defined custom grid. What it does is give you a distance, or range, in which the cursor can be away from an object but still snap to the object's hotspot (eg. the center of a pad). Object hotspot snapping overrides a snap grid, allowing you to easily connect to an off-grid object. Use the Shift+E keyboard shortcut to cycle through the three modes (Off, Current Layer, All Layers). For more information, see Object Snapping.
Defining the Purpose of a Grid
A local grid can be used in a variety of situations:
- In the placement of non-component objects only.
- In the placement of components only.
- In the placement of both non-component objects and components.
Definition of how a grid can be used - its purpose or application - is performed using the Comp and Non Comp options, associated with that grid's entry in the Grid Manager section of the Properties panel.
Use the Comp and Non Comp options to determine local grid application.
The following animation illustrates an example of using a local Polar Grid for component placement in the PCB Editor. The grid has been defined for use with components only, and so only appears when a component starts to be moved. This example also illustrates a great feature of polar grids - automatic placement rotation. As you move a component over a defined grid of this type, it will automatically rotate to the origin of the grid, as you move it around the grid. Use this feature, in combination with standard object rotation - Spacebar (anti-clockwise), Shift+Spacebar (clockwise) - to align your components exactly as you need them.
An example of component placement on a component-only local Polar Grid.
Defining the Grid Display
For any custom grid you define, as well as the
Global Board Snap Grid, options are provided to control how the grid is presented visually in the workspace. Two levels can be defined:
- Fine - the fine-level display grid is for when you are more zoomed-in. The grid markers for this level of grid display follow directly the defined step sizes for the grid.
- Coarse - the optional coarse-level display grid comes into play as you zoom out. The grid markers for this level of grid display are based on a specified multiple of the defined step sizes.
Example Cartesian grid with fine- and coarse-level display grids presented in the workspace. Left: Fine-level displayed using dots, coarse-level using Lines. Right: Both fine- and
coarse-level grids displayed using Lines.
Nesting and Grid Priority
The local grids you define in the Grid Manager section of the Properties panel can be freely stacked within the board area. By specifying origin coordinates accordingly, grids can be overlapped, creating a nested hierarchy of grids, with which to fine tune placement of design objects as you layout your board.
Grid contention - which grid in an overlapping stackup of grids should a design object snap to - is resolved using a priority system. Each local placement grid you create and define is given a numbered priority. By default, each new grid is given the highest priority of
1, with all existing grids moved down in priority accordingly.
In the workspace, priority is distinguished by drawing order. The highest priority grid (priority
1) will be drawn in front of all other grids, then the grid with priority level
2, and so on, down to the default
Global Board Snap Grid, which is drawn behind all other custom grids.
An example of three nested Polar grids. The Yellow Polar Grid has the highest priority and appears on top. The Red Polar Grid is next priority, appearing behind the yellow grid,
but in front of the aqua grid. The default grid appears behind all of these grids, as all custom grids take precedence over it in the priority stakes.
Disabling a Grid
There may be occasion where a grid isn't needed while placing or moving a particular design object. Rather than deleting the grid - it may be needed again later, in the same or different area of the board - it can simply be 'hidden' from the workspace. This can be achieved by disabling the grid's associated Comp and Non Comp attributes, in the Grid Manager section of the Properties panel.
Disable a local grid to effectively hide it, therefore preventing objects snapping to it. Using the nested grids example, the Red Polar grid has been disabled. As the grid has not
been deleted, you can re-enable and use again when needed, without having to redefine it!
Deleting a Grid
Custom grids can be deleted simply by selecting their corresponding entry in the Grid Manager section of the Properties panel, and clicking the button. You will be asked to confirm the deletion - click Yes to do so.
Snap Guides are special objects that are manually placed specifically for the purpose of driving the cursor-snap on a certain axis or point - assisting in object/component placement. They can also serve as a visual indicator for general layout or alignment purposes. The following types of snap guide are supported:
- Linear Guide - a line-style guide that can be horizontal, vertical or +/- 45 Degrees.
- Point Guide - a point-style guide offering finer control over object placement. It is simply a hotspot that is manually marked within the confines of a defined grid.
Any number of snap guides can be defined for the workspace, with controls for placement and management available from the Guide Manager section of the Properties panel (accessed when there are no design objects currently selected in the design workspace). And while controls are available for adding new snap guides from within this section (from the button), it is far easier to visually add them (from the button) directly in the workspace, then fine-tune them as required.
Snap Guides can also be placed using commands available from the Place » Work Guides sub-menu.
The Guide Manager section of the Properties panel - command central for managing visual placement guides for use in the workspace.
Shown here are examples of the various Snap Guides available to assist object placement.
During an interactive process such as placing or moving, the cursor will snap to a placed Linear Guide, at the point where that guide intersects a defined grid. Using a Linear Guide, objects can quickly be aligned simply by dragging them until they 'snap' against the guideline. For a Point Guide, the hotspot for the object being moved will 'snap' to the guide when it passes into close proximity with it.
Disabling a Guide
There may be occasion where a snap guide isn't needed while placing or moving a particular design object. Rather than deleting the guide since it may be needed again later in the same or different area of the board, it can be 'hidden' from the workspace. This can be achieved by disabling the guide's associated Enabled attribute in the Guide Manager section of the Properties panel.
Disable a snap guide to effectively hide it, therefore preventing objects snapping to it. In this image, the +45 and -45 guides have
been disabled. As the guides have not been deleted, you can re-enable and use them again when needed, without having to redefine
Deleting a Guide
To delete a snap guide, select its entry in the Guide Manager section of the Properties panel, and click the button. You will be asked to confirm the deletion - click Yes to do so.