Draft PathArray

Description
The PathArray tool places copies of a selected shape along a selected path. The path can be a wire or one or more edges.

The shapes can optionally be aligned with the tangent of the path. If required, a translation Vector can be specified to shift the shapes so the centroid is on the path.



How to use

 * 1) Select an object which you wish to distribute.
 * 2) Select a path object or some edges along which the object will be distributed.
 * 3) Press the  button.

The base object should be centred around the origin, even if the path starts somewhere else.

The count, alignment, and position of the copies along the path can be changed after creation by changing its properties.

Options
There are no options for this tool. Either it works with the selected object or not.

Properties

 * : specifies the object to duplicate in the path.
 * : specifies the path object.
 * : specifies the sub-elements (edges) of the path object. This property does not yet appear in the property editor.
 * : specifies the number of copies of the base object.
 * : if it is the copies are aligned to the path; otherwise they are left in their default orientation.
 * in certain cases the shape will appear flat, in reality it may have moved in the 3D space, so instead of using a flat view, change the view to axonometric.


 * : specifies a translation vector (x, y, z) to displace each copy along the path.
 * when is, the vector is relative to the local tangent, normal or binormal coordinates; otherwise the vector is relative to the global coordinates.

Scripting
The PathArray tool can by used in macros and from the python console by using the following function:


 * Distribute count copies of a document shapeobject along a pathobject or subobjects of a pathobject. Optionally translates each copy by FreeCAD.Vector xlate direction and distance to adjust for difference in shape centre vs shape reference point. Optionally aligns baseobject to tangent/normal/binormal of path.

Example:

Technical Explanation
When "Align = false", PathArray's logic is quite easy to understand.

When "Align = true" the logic is a bit harder to grasp:
 * 1) Construct Frenet coordinate systems on the path (X is tangent, Z is normal, Y is binormal).
 * 2) Copy the original object to every on-path coordinate system, so that the global origin is matched with the on-path coordinate system origin.

It is much easier to understand with pictures. The following images show how the array is produced, depending on which plane is the path.



Path on XY Plane



Path on XZ Plane



Path on YZ Plane

The clear advantage of this logic is that as you reorient the path but not the object, the result is consistent - object remains aligned to the path the way it was before reorienting the path.

(Thanks to @DeepSOIC for this explanation)