[API] Why is `massproperties` returning three separate sets of data?

kenn_sebesta167

When using the `massproperties` endpoint, we get three sets of data. Three 3D centroids, three masses, three tensor matrices for moment of inertia...

Finding docu on the API calls has been elusive, but when I look at the data, it's consistent with some kind of low/medium/high estimate. Although it seems to be presented as medium/low/high. Even then, there's some data formatting issues, such as 'centroid' and 'inertia' being flat arrays, instead of 3 arrays of 3D arrays whereas 'principal_axes' is split into three arrays of 3D tuples.

1. Anyone know what's going on? 
2. Is this a stable API output or should we expect things to evolve in the future?

Sample output

{
	'bodies': {
		'-all-': {
			'centroid': [-1.0042503280088468e-05,
				1.482968868956767,
				-0.10850477404260045,
				-0.0004082241547197037,
				1.4714758672098183,
				-0.11013804119136905,
				0.0003880814213651826,
				1.494527929574006,
				-0.10688083594369849
			],
			'has_mass': True,
			'inertia': [714.867020569292,
				-0.014160378394796422,
				0.004015898147491597,
				-0.014160378394796422,
				1131.586050729513,
				-53.50925669683793,
				0.004015898147491597,
				-53.50925669683793,
				1562.5523468371136,
				701.8487106243456,
				-5.522840015221163,
				-1.1145415625960162,
				-5.522840015221163,
				1111.699098197347,
				-59.31222835505792,
				-1.1145415625960162,
				-59.31222835505792,
				1548.9104146980378,
				729.4246845262535,
				5.4938937031232715,
				1.1225860729708868,
				5.4938937031232715,
				1151.461202245161,
				-47.47341185240581,
				1.1225860729708868,
				-47.47341185240581,
				1577.7024981879326
			],
			'mass': [1108.1590500187838,
				1104.9831903079348,
				1111.3349097296327
			],
			'mass_missing_count': 0,
			'periphery': [28.54436749362015,
				28.52381150513451,
				28.564923482105787
			],
			'principal_axes': [{
					'x': -0.9999999994305906,
					'y': -3.3645025311420136e-05,
					'z': 2.6136796041127386e-06
				},
				{
					'x': -3.307887953955009e-05,
					'y': 0.992603752707567,
					'z': 0.12139929578314308
				},
				{
					'x': 6.678830562829961e-06,
					'y': -0.12139929562755955,
					'z': 0.9926037532553086
				}
			],
			'principal_inertia': [714.8670200823695,
				1125.0416611936616,
				1569.0967368598874
			],
			'volume': [1.4441004096515049,
				1.4393286387365865,
				1.4488721805664238
			]
		}
	},
	'microversion_id': '80f46668d060ca5fd7bc9cc4'
}