Position and orientation in the reference frame of a LCS

[josegegas]

Hi.

Is there a way to get the position and orientation of, say, a point and a line, respectively, in the reference frame of a local coordinate system?

[chrisb]

As nobody answered until now, I can show you a rather complicated non parametric workaround:
- create a ShapeBinder of the global object
- set TraceSupport=True
- attach something to the ShapeBinder
- detach it

-> now the formerly attached object has the placement in local coordinates of the global object

[openBrain]

Hi.

Is there a way to get the position and orientation of, say, a point and a line, respectively, in the reference frame of a local coordinate system?

Is Python scripting allowed ? For better understanding, please provide sample file with said point, line & LCS

[josegegas]

I am no talking about using the GUI, but Python. Imagine I create a local coordinate system at any given position and orientation. Then I want to get the coordinates of any point (or another LCS), not relative to the global coordinate system, but relative to the first LCS. It would also be great if it was possible to get the orientation of a given line, again, not relative to the global coordinate system, but relative to the LCS...

So far I have been using Sympy for these purposes:

https://docs.sympy.org/latest/modules/v ... rdsys.html

As you can see Sympy allows creating coordinate systems that are translated and rotated relative to one another, and then obtaining the relative positions and orientations as seen from any coordinate system. I would like to know if it is possible to do the same using FreeCAD, and I though local coordinate systems may allow so.

[openBrain]

I am no talking about using the GUI, but Python. Imagine I create a local coordinate system at any given position and orientation. Then I want to get the coordinates of any point (or another LCS), not relative to the global coordinate system, but relative to the first LCS.

If I get it correctly, it's as simple as :

Code: Select all

LCS.getGlobalPlacement().inverse().multiply(OBJ.getGlobalPlacement())

[chrisb]

I am no talking about using the GUI, but Python.

Moved to Python forum.

[galou_breizh]

If I get it correctly, it's as simple as :

Code: Select all

LCS.getGlobalPlacement().inverse().multiply(OBJ.getGlobalPlacement())

Beware! This is misleading as getGlobalPlacement does not work for links (it shows the global placement of the original object). See the GetGlobalPlacement macro for a version supporting links.

Gaël

[openBrain]

Beware! This is misleading as getGlobalPlacement does not work for links (it shows the global placement of the original object). See the GetGlobalPlacement macro for a version supporting links.

Why not fixing the code ?

[edwilliams16]

Beware! This is misleading as getGlobalPlacement does not work for links (it shows the global placement of the original object). See the GetGlobalPlacement macro for a version supporting links.

Why not fixing the code ?

It does seem like a bug/deficiency. A linked object either has no getGlobalPlacement() method, or the method returns the global placement of the original, not the linked object. The global placement can be obtained by multiplying up the placements of the chain of objects starting at the root, as described in the https://forum.freecadweb.org/viewtopic.php?f=22&t=64608 thread and nicely implemented by @galou_breizh in his macro.
It makes the method less useful when you need to write your own if you want it to apply to linked objects.

[openBrain]

It does seem like a bug/deficiency. A linked object either has no getGlobalPlacement() method, or the method returns the global placement of the original, not the linked object.

Looks like something that can be very improved IMO. A link object should return its global placement when 'getGlobalPlacement' is called on it. No reason to return something else.