Selecting a part from hierarchy of assemblies

[xbit]

Before asking, i always search the API, or at least try to search the API, because i cannot always find stuff.
Can you send me a link of a good reference to learn?
Perhaps i am browsing the wrong resources.

Anyway i get a strange error from your snippet (i also added Part.Compound(ssh))

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ssh = sh.SubShapes.copy()
scaling_matrix = App.Matrix(x_scale,0,0,0,  0,y_scale,0,0,  0,0,z_scale,0,  0,0,0,1)
scaling_center = ssh[0].BoundBox.Center
global_matrix = App.Matrix()
global_matrix.transform(scaling_center, scaling_matrix
ssh[0].transformGeometry(global_matrix)
newPart = Part.Compound(ssh)
newPart.exportStep(STEP_FilenameAndPath)

The error is:

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    ssh[0].transformGeometry(global_matrix)
    ^
SyntaxError: invalid syntax

Thank you very much for your help!

[openBrain]

Before asking, i always search the API, or at least try to search the API, because i cannot always find stuff.
Can you send me a link of a good reference to learn?
Perhaps i am browsing the wrong resources.

I have no link.
To work with TopoShape, I search the TopoShape API. To work with transformation matrices, I search the Matrix API. Etc...

Anyway i get a strange error from your snippet (i also added Part.Compound(ssh))

Not really strange. The closing parenthesis is missing on the line above the one with the error.
I edited my previous post to fix but hey, kind of things you should be able to find by yourself.

[xbit]

Sorry for my shortsight.

Anyway, the script still does not function.
The resulting file is the same as the original with no changes to the subShape

[openBrain]

Sorry for my shortsight.

Anyway, the script still does not function.
The resulting file is the same as the original with no changes to the subShape

Indeed

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ssh[0].transformGeometry(global_matrix)

shall be replaced by

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ssh[0] = ssh[0].transformGeometry(global_matrix)

or

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ssh[0].transformShape(global_matrix)

Any of both is right.

[xbit]

Thank you very much my friend!
You're the man.

[xbit]

If i also want to perform translation and rotation to the selected part, what would you suggest, in terms of API?

Could you guide me on where to look?

I don't know what function to use for translation - nor do know where to look exactly.

As for rotation, i tried the .rotate() function i have already used, to no effect.
This is my code:

Code: Select all

x_axis = 0
y_axis = 0
z_axis = 0

#NOTE: The elements of sys.argv are strings, you need to convert them to 
#integers before comparing with integers.

#the second argument is the axis to rotate (1-3 for axis x,y,z)
axis_Select = int(sys.argv[2])
#the third argument is the angle, for the axis we specified in the second arg
angle = int(sys.argv[3])

if axis_Select == 1:
	x_axis = 1
elif axis_Select == 2:
	y_axis = 1
elif axis_Select == 3:
	z_axis = 1


ssh = sh.SubShapes.copy()

ssh[0] = ssh[0].rotate(FreeCAD.Vector(0,0,0), FreeCAD.Vector(x_axis, y_axis, z_axis), angle)

newPart = Part.Compound(ssh)
newPart.exportStep(STEP_FilenameAndPath)

[openBrain]

If i also want to perform translation and rotation to the selected part, what would you suggest, in terms of API?

Could you guide me on where to look?

I don't know what function to use for translation - nor do know where to look exactly.

You can add functions to your matrix (not tested) :

Code: Select all

scaling_matrix = App.Matrix(x_scale,0,0,0,  0,y_scale,0,0,  0,0,z_scale,0,  0,0,0,1)
scaling_center = ssh[0].BoundBox.Center
move_vector = App.Vector(10,10,10) # to be changed
rotx_angle = 45 # to be changed
roty_angle = 45 # to be changed
rotz_angle = 45 # to be changed
global_matrix = App.Matrix()
global_matrix.transform(scaling_center, scaling_matrix)
global_matrix.move(move_vector)
global_matrix.rotateX(rotx_angle*math.pi/180)
global_matrix.rotateY(roty_angle*math.pi/180)
global_matrix.rotateZ(rotz_angle*math.pi/180)

Need to 'import math'
Have a look at : https://wiki.freecadweb.org/Matrix_API

[xbit]

Thank you openBrain.

Unfortunately, your snippet did not work.
And with my attempt, that makes it two different aproaches that did not work.


I tried many iterations with your code and none of them worked.

I researched all the function calls in the API and some things are unclear for me.

1. Why are you using a scaling_matrix, for rotation only operations?
2. Is this line necessary?
3. Why do you use global_matrix.move()?

I am having trouble understanding your rotation philosophy....

[xbit]

I brushed up my knowledge on linear algebra and transformation matrices. (https://www.varsitytutors.com/hotmath/h ... -rotations)

We need the center of rotation.
So this line of code makes sense:

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scaling_center = ssh[0].BoundBox.Center

(of course we don't do scaling, but you get the point, i kept the naming convention, in order to compare with your code).

We obviously have the rotation values:

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rotx_angle = 45 # to be changed
roty_angle = 45 # to be changed
rotz_angle = 45 # to be changed

I do not understand the purpose of the move_vector code:

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move_vector = App.Vector(10,10,10)
global_matrix.move(move_vector)

In order to rotate around a given axis, isn't it valid if we get the rotation matrix (for the given deegrees) and then perforn a transform on the part matrix, with the transformation matrix, in regards to the center of axis?

[openBrain]

Unfortunately, your snippet did not work.
And with my attempt, that makes it two different aproaches that did not work.

Works good here. You may have to had some extra lines to manage the rotation center though.
[/quote]
1. Why are you using a scaling_matrix, for rotation only operations?
[/quote]
Because you said you want also a rotation and a move. Not only a rotation

2. Is this line necessary?

See above

3. Why do you use global_matrix.move()?

Because you said you want a translation...


Here's a complete detailed snippet with comments

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import Part
import FreeCAD as App
import math

sh = Part.read(PATH_TO_STEP) # replace with correct path
ssh = sh.SubShapes.copy()
### Define the center point used for transformations
trans_center = ssh[0].BoundBox.Center # replace by what you want to get as center for transformations
### Define the scaling transformation matrix
scaling_matrix = App.Matrix(2,0,0,0,  0,2,0,0,  0,0,2,0,  0,0,0,1) # replace '2" by scaling factor
### Define the rotation transformation matrix
rotx = App.Matrix()
rotx.rotateX(45*math.pi/180) # replace '45' by rotation angle around x in degrees
roty = App.Matrix()
roty.rotateY(45*math.pi/180) # replace '45' by rotation angle around y in degrees
rotz = App.Matrix()
rotz.rotateZ(45*math.pi/180) # replace '45' by rotation angle around z in degrees
### Define the translation transformation vector
move_vector = App.Vector(10,10,10) # replace '10' by needed translation
### Compute the global matrix
global_matrix = App.Matrix() # initialize the global transformation matrix
global_matrix.transform(trans_center, scaling_matrix) # apply scaling first (so axis are still correct, before rotation)
global_matrix.transform(trans_center, rotx) # apply rotation then (so center is still correct, before move)
global_matrix.transform(trans_center, roty) # apply rotation then (so center is still correct, before move)
global_matrix.transform(trans_center, rotz) # apply rotation then (so center is still correct, before move)
global_matrix.move(move_vector)
### Apply the matrix to the subshape
ssh[0] = ssh[0].transformGeometry(global_matrix)

newPart = Part.Compound(ssh)
newPart.exportStep(STEP_FilenameAndPath)