124 lines
3.6 KiB
Python
124 lines
3.6 KiB
Python
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"""
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units.py
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--------------
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Deal with physical unit systems (i.e. inches, mm)
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Very basic conversions, and no requirement for
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sympy.physics.units or pint.
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"""
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import json
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from .constants import log
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from . import resources
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# scaling factors from various unit systems to inches
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TO_INCH = json.loads(resources.get('units_to_inches.json'))
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def unit_conversion(current, desired):
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"""
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Calculate the conversion from one set of units to another.
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Parameters
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---------
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current : str
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Unit system values are in now (eg 'millimeters')
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desired : str
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Unit system we'd like values in (eg 'inches')
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Returns
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---------
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conversion : float
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Number to multiply by to put values into desired units
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"""
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current = str(current).strip().lower()
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desired = str(desired).strip().lower()
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conversion = TO_INCH[current] / TO_INCH[desired]
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return conversion
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def units_from_metadata(obj, guess=True):
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"""
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Try to extract hints from metadata and if that fails
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guess based on the object scale.
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Parameters
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------------
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obj: object
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Has attributes 'metadata' (dict) and 'scale' (float)
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guess : bool
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If metadata doesn't indicate units, guess from scale
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Returns
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------------
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units: str
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A guess of what the units might be
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"""
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# try to guess from metadata
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for key in ['file_name', 'name']:
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if key not in obj.metadata:
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continue
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# get the string which might contain unit hints
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hints = obj.metadata[key].lower()
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if 'unit' in hints:
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# replace all delimiter options with white space
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for delim in '_-.':
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hints = hints.replace(delim, ' ')
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# loop through each hint
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for hint in hints.strip().split():
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# key word is "unit" or "units"
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if 'unit' not in hint:
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continue
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# get rid of keyword and whitespace
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hint = hint.replace(
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'units', '').replace(
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'unit', '').strip()
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# if the hint is a valid unit return it
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if hint in TO_INCH:
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return hint
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if not guess:
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raise ValueError('no units and not allowed to guess')
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# we made it to the wild ass guess section
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# if the scale is larger than 100 mystery units
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# declare the model to be millimeters, otherwise inches
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log.warning('no units: guessing from scale')
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if float(obj.scale) > 100.0:
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return 'millimeters'
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else:
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return 'inches'
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def _convert_units(obj, desired, guess=False):
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"""
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Given an object with scale and units try to scale
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to different units via the object's `apply_scale`.
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Parameters
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---------
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obj : object
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With apply_scale method (i.e. Trimesh, Path2D, etc)
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desired : str
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Units desired (eg 'inches')
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guess: bool
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Whether we are allowed to guess the units
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if they are not specified.
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"""
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if obj.units is None:
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# try to extract units from metadata
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# if nothing specified in metadata and not allowed
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# to guess will raise a ValueError
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obj.units = units_from_metadata(obj, guess=guess)
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log.info('converting units from %s to %s', obj.units, desired)
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# float, conversion factor
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conversion = unit_conversion(obj.units, desired)
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# apply scale uses transforms which preserve
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# cached properties (rather than just multiplying vertices)
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obj.apply_scale(conversion)
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# units are now desired units
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obj.units = desired
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