def get_angle_unit_data(sum_df, **kwargs):
	"""
	Function: get angle unit information from measured target positions.
	Input:
	- sum_df: DataFrame. processed DataFrame that contains both bundle heel and target info and growth cone length and angle info.
	- kwargs: additional parameters
		- 'criteria': Dataframe with Boolean values. filtering which bundles to include in the calculation.
	Output:
	- phi_unit: radian value of "1" in standardized coordinate.
	"""

	if('criteria' in kwargs.keys()):
		criteria = kwargs['criteria']
		sum_df = sum_df.loc[criteria, :]

	# print(f"get_angle_unit_num={len(sum_df)}")
	phi_unit = sum_df['aT3cT7'].mean()/2

	return phi_unit