density property on TPMS class

[ricardo0115]

Description

The following code snippet raises an AssertionError:

from microgen import Tpms
from microgen.shape.surface_functions import gyroid

geometry = Tpms(
    surface_function=gyroid,
    offset=0.16,
    resolution=30,
)

assert geometry.density is not None

After checking the implementation, it seems that the Tpms class currently cannot compute the density of a TPMS structure when it is initialized using an offset rather than a density.
(See [tpms.py#L43](

microgen/microgen/shape/tpms.py

Line 43 in ae275ed

class Tpms(Shape):

))

Suggestion

It might be useful to:

• Add a density property to the Tpms class that can handle geometries defined via offset,
  or
• Clarify in the documentation that density is unavailable when an offset is used.

@kmarchais please let me know if I’m misunderstanding how the API is intended to be used 🙂

[kmarchais]

Hi,

Thanks for the report. Indeed, a density property is missing here.
The thing is that, depending on which part the user wants to generate (sheet or skeletal), the density will be different. For instance, this is not known in your example.

[ricardo0115]

Hi @kmarchais, maybe we should think a possible design rework to handle this usecase ? Maybe passing the part type of the TPMS at initialization ?
What do you think ? We can also add @rdesparbes to have an opinion about this topic.

[rdesparbes]

Hello @kmarchais @ricardo0115,

In the code snippet of this issue, I am not particularly shocked by the fact that density stays None if it is not provided in the constructor.

However, I took a look at the implementation, there are some other behaviors that are not very intuitive:

from microgen import Tpms
from microgen.shape.surface_functions import gyroid

def test_accessing_fields_keeps_the_object_unchanged() -> None:
    geometry = Tpms(
        surface_function=gyroid,
        resolution=30,
        density=1.0,
    )

    assert geometry.offset is None
    geometry.grid_sheet  # I would expect this statement to keep the public fields of the object unchanged
    assert geometry.offset is None  # Actually equal to 2.9956002415533716