Std LinkMake

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Menu location
Std LinkMake
None
Workbenches
All
Default shortcut
None
Introduced in version
0.19
See also
Std Part, Std Group, PartDesign Body

Description

Std LinkMake creates an App Link (App::Link class), a type of object that references or links to another object, in the same document, or in another document. It is especially designed to efficiently duplicate a single object multiple times, which helps with the creation of complex assemblies from smaller subassemblies, and from multiple reusable components like screws, nuts, and similar fasteners.

The App Link object was newly introduced in v0.19; in the past, simple duplication of objects could be achieved with Draft Clone, but this is a less efficient solution due to its implementation which essentially creates a copy of the internal Shape of the source object. On the other hand, a Link references directly the original Shape, so it is more memory efficient.

By itself the Link object can behave like an array, duplicating its base object many times; this can be done by setting its DataElement Count property to 1 or larger. This "Link array" object can also be created with the different array tools of the Draft Workbench, for example, Draft OrthoArray, Draft PolarArray, and Draft CircularArray. When used with the PartDesign Workbench, Links are intended to be used with full PartDesign Bodies; to create arrays of features, use PartDesign LinearPattern, PartDesign PolarPattern, and PartDesign MultiTransform.

The Std LinkMake tool is not defined by a particular workbench, but by the base system, thus it is found in the structure toolbar that is available in all workbenches. The Link object, used in conjunction with Std Part to group various objects, forms the basis of the Assembly3 and Assembly4 Workbenches.

Usage

With selection:

Select an object in the tree view or 3D view for which you wish to create a Link.
Press the Std LinkMake button. The produced object has the same icon as the original object, but has an arrow overlay indicating it is a Link.

Without selection:

If no object is selected, press the Std LinkMake button to create an empty Link.
Go to the property editor, then click on the DataLinked Object property to open the Link selection dialog to choose an object, then press OK.
Instead of choosing an entire object in the tree view, you can also pick subelements (vertices, edges, or faces) of a single object in the 3D view. In this case, the Link will duplicate only these subelements, and the arrow overlay will be different.

Properties

An App Link (App::Link class) is derived from the basic App DocumentObject (App::DocumentObject class), therefore it has the latter's basic properties like DataLabel and DataLabel2.

The following are the specific properties available in the property editor. Hidden properties can be shown by using the Show all command in the context menu of the property editor.

Data

Link

DataLinked Object (XLink): it indicates the source object of the App Link; this can be an entire object, or a subelement of it (vertex, edge, or face).
DataLink Transform (Bool): it defaults to false, in which case the Link will override the DataLinked Object's own placement. If it is set to true, the Link will be placed in the same position as the DataLinked Object, and its placement will be relative to the DataLinked Object's placement. This can also be achieved with Std LinkMakeRelative.
DataPlacement (Placement): the placement of the Link in absolute coordinates.
Data (Hidden)Link Placement (Placement): it is an offset applied on top of the DataPlacement of the DataLinked Object. This property is normally hidden but appears if DataLink Transform is set to true; in this case, DataPlacement now becomes hidden.
DataShow Element (Bool): it defaults to true, in which case the tree view will show the individual Link copies, as long as DataElement Count is 1 or larger.
DataElement Count (IntegerConstraint): it defaults to 0. If it is 1 or larger, the App Link will behave like an array, and will duplicate the same DataLinked Object many times. If DataShow Elements is true, each element in the array will be displayed in the tree view, and each can have its own DataPlacement modified. Each Link copy will have a name based on the Link's Name, augmented by _iN, where N is a number starting from 0. For example, with a single Link, the copies will be named Link_i0, Link_i1, Link_i2, etc.
DataLink Execute (String): name of the execute function that will run for this particular Link object. It defaults to 'appLinkExecute'. Set it to 'None' to disable it.
Data (Hidden)Colored Elements (LinkSubHidden): list of Link elements that have had their color overriden.
DataScale (Float): it defaults to 1.0. It is a factor for uniform scaling in each direction X, Y, and Z. For example, a cube of 2 mm x 2 mm x 2 mm, that is scaled by 2.0, will result in a shape with dimensions 4 mm x 4 mm x 4 mm.
Data (Hidden)Scale Vector (Vector): the scale factor for each component (X, Y, Z) for all Link elements when DataElement Count is 1 or larger. If DataScale is other than 1.0, this same value will be used in the three components.
DataScale List (VectorList): the scale factor for each Link element.
Data (Hidden)Visibility List (BoolList): (read-only) the visibility state of each Link element, either true or false.
Data (Hidden)Placement List (PlacementList): (read-only) the placement for each Link element.
Data (Hidden)Element List (LinkList): the list of Link elements.
Data (Hidden)_LinkTouched (Bool):
Data (Hidden)_ChildCache (LinkList):

Base

Data (Hidden)Proxy (PythonObject): a custom class associated with this object. This only exists for the Python version. See Scripting.

The App Link object will additionally show the properties of the original DataLinked Object, so the property editor may have groups of properties like Attachment, Box, Draft, etc.

View

Link

ViewDraw Style (Enumeration): it defaults to None; it can be Solid, Dashed, Dotted, Dashdot; defines the style of the edges in the 3D view.
ViewLine Width (FloatConstraint): a float that determines the width in pixels of the edges in the 3D view. It defaults to 2.0.
ViewOverride Material (Bool): it defaults to false; if set to true it will override the DataLinked Object's material, and it will display the colors defined in ViewShape Material.
ViewPoint Size (FloatConstraint): similar to ViewLine Width, defines the size of the vertices.
ViewSelectable (Bool): if it is true, the object can be picked with the pointer in the 3D view. Otherwise, the object cannot be selected until this option is set to true.

ViewShape Material (Material): this property includes sub-properties that describe the appearance of the object.
- ViewDiffuse Color, it defaults to (0.4, 1.0, 1.0), which is displayed as [102, 255, 255] on base 255, light blue .
- ViewAmbient Color, it defaults to (0.2, 0.2, 0.2), which is displayed as [51, 51, 51] on base 255, dark gray .
- ViewSpecular Color, it defaults to (0.0, 0.0, 0.0), which is displayed as [0, 0, 0] on base 255, black .
- ViewEmissive Color, it defaults to (0.0, 0.0, 0.0), which is displayed as [0, 0, 0] on base 255, black .
- ViewShininess, it defaults to 0.2
- ViewTransparency, it defaults to 0.0.

Base

View (Hidden)Child View Provider (PersistentObject):
View (Hidden)Material List (MaterialList): (read-only) if individual materials have been added, they will be listed here.
View (Hidden)Override Color List (ColorList): (read-only) if the individual faces or edges of the link have been overridden they will be listed here.
View (Hidden)Override Material List (BoolList): (read-only) if the individual materials of the link have been overridden they will be listed here.

Display Options

ViewDisplay Mode (Enumeration): 'Link' or 'ChildView'.
ViewShow In Tree (Bool): see the information in App FeaturePython.
ViewVisibility (Bool): see the information in App FeaturePython.

Selection

ViewOn Top When Selected (Enumeration): see the information in App FeaturePython.
ViewSelection Style (Enumeration): see the information in App FeaturePython.

It will additionally show the view properties of the original DataLinked Object.

Inheritance

An App Link is formally an instance of the class App::Link, whose parent is the basic App DocumentObject (App::DocumentObject class). It is a very low level object, which can be used with most other document objects.

Simplified diagram of the relationships between the core objects in the program. The App::Link object is a core component of the system, it does not depend on any workbench, but it can be used with most objects created in all workbenches.

Scripting

See also: FreeCAD Scripting Basics, and scripted objects.

See Part Feature for the general information.

An App Link is created with the addObject() method of the document. It can define its DataLinked Object by overriding its LinkedObject attribute, or by using its setLink method.

import FreeCAD as App

doc = App.newDocument()
bod1 = App.ActiveDocument.addObject("PartDesign::Body", "Body")
bod2 = App.ActiveDocument.addObject("Part::Box", "Box")

obj1 = App.ActiveDocument.addObject("App::Link", "Link")
obj2 = App.ActiveDocument.addObject("App::Link", "Link")

obj1.LinkedObject = bod1
obj2.setLink(bod2)
App.ActiveDocument.recompute()

The basic App::Link doesn't have a Proxy object so it can't be fully used for sub-classing.

Therefore, for Python subclassing, you should create the App::LinkPython object.

import FreeCAD as App

doc = App.newDocument()
obj = App.ActiveDocument.addObject("App::LinkPython", "Link")
obj.Label = "Custom label"

The App Link object was introduced after 2 years of development and prototyping. This component was thought and developed almost single-handedly by user realthunder. The motivations and design implementations behind this project are described in his GitHub page, Link. In order to accomplish this feature, several core changes to FreeCAD were made; these were also extensively documented in Core-Changes.

The App Link project started after the redesign of the PartDesign Workbench was complete in v0.17. The history of App Link can be traced to some essential forum threads: