Enable `mach_cad` to handle default unit systems in JMAG

[noguchi-takahiro]

Abstract

Enable mach_cad to handle default unit systems in JMAG

Context

When we launch JMAG geometry editor through mach_cad, the only available unit system is SI Unit, e.g., length units are restricted to meters. See below:

eMach/mach_cad/tools/jmag/jmag.py

Lines 410 to 423 in a86c775

	def set_default_length_unit(self, user_unit):
	"""Set the default length unit in JMAG. Only DimMeter supported.
	Args:
	user_unit: String representing the unit the user wishes to set as default.
	Raises:
	TypeError: Incorrect dimension passed
	"""
	if user_unit == "DimMeter":
	self.default_length = user_unit
	self.model.SetUnitCollection("SI_units")
	else:
	raise Exception("Unsupported length unit")

However, we often prefer millimeters when designing the electric machines, which is actually the default unit system within JMAG. This means that mach_cad tries to change this default unit to be SI unit. It looks like mach_cad already has functionality to switch unit systems, but if we specify any unit system other than SI unit, it results in error as "Unsupported length unit"

Approach

One possible improvement is to modify to support JMAG’s default unit system and allow switching to not SI units without causing errors. For example,

    def set_default_length_unit(self, user_unit):
        """Set the default length unit in JMAG. Only DimMeter supported.

        Args:
            user_unit: String representing the unit the user wishes to set as default.

        Raises:
            TypeError: Incorrect dimension passed
        """
        if user_unit == "DimMeter":
            self.default_length = user_unit
            self.model.SetUnitCollection("SI_units")
        elif user_unit == "default":
            self.default_length = user_unit
            self.model.SetUnitCollection("default")
        else:
            raise Exception("Unsupported length unit")

[elsevers]

Thanks @noguchi-takahiro. Does the dim_millimeter class here do what you are looking for?

[noguchi-takahiro]

Thank you @elsevers. In my understanding, the DimMillimeter class just represents a unit rather than unit conversion, i.e., it does not do any X1000 or 1/1000. The purpose of this should explicitly indicate that a given value is in millimeters.

Even if I add DimMillimeter in

eMach/examples/mach_cad_examples/example_spm.py

Line 123 in a86c775

tool_jmag.open(comp_filepath=file, study_type="Transient")

as follows:

tool_jmag.open(comp_filepath=file, length_unit="DimMillimeter", study_type="Transient")

this would raise error as I describe here.

[noguchi-takahiro]

@elsevers When I create my own analyzer based on mach_cad, it would be really useful to make the unit in JMAG to be mm. What do you think about this approach described here? Do you have other suggestion, or we should not make any changes here?

[elsevers]

Thanks @noguchi-takahiro. Adding the elif code that you suggest seems okay to me.

Would there be other parts of the code base that would need to change as well to make this help you?

[noguchi-takahiro]

Thank you @elsevers. I am trying to implement this soon by creating a PR.

Would there be other parts of the code base that would need to change as well to make this help you?

I found a similar statement in tools/jmag/JMAG_Designer.m:

https://github.com/Severson-Group/eMach-matlab/blob/cc6337de94e853f9f9f15c56f6b7e874431b8bce/tools/jmag/JMAG_Designer.m#L411-L416

This is Matlab version to set an unit. Do you think we want to change the same for this code?

UPDATE: it looks like this code above is no longer from eMach repo but eMach-matlab.

[elsevers]

Thanks @noguchi-takahiro -- you are right that eMach-matlab is a separate repo.

Go ahead and submit a PR for the changes you'd like to make.