text: #   This Python module is part of the PyRate software package.
  #
  #   Copyright 2017 Geoscience Australia
  #
  #   Licensed under the Apache License, Version 2.0 (the "License");
  #   you may not use this file except in compliance with the License.
  #   You may obtain a copy of the License at
  #
  #       http://www.apache.org/licenses/LICENSE-2.0
  #
  #   Unless required by applicable law or agreed to in writing, software
  #   distributed under the License is distributed on an "AS IS" BASIS,
  #   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  #   See the License for the specific language governing permissions and
  #   limitations under the License.
  """
  This Python module contains a collection of constants used in
  various components of the PyRate software
  """
  
  # lookup keys for the metadata fields in PyRate GeoTIFF files
  PYRATE_NCOLS = 'NCOLS'
  PYRATE_NROWS = 'NROWS'
  PYRATE_X_STEP = 'X_STEP'
  PYRATE_Y_STEP = 'Y_STEP'
  PYRATE_LAT = 'LAT'
  PYRATE_LONG = 'LONG'
  MASTER_DATE = 'MASTER_DATE'
  MASTER_TIME = 'MASTER_TIME'
  SLAVE_DATE = 'SLAVE_DATE'
  SLAVE_TIME = 'SLAVE_TIME'
  EPOCH_DATE = 'EPOCH_DATE'
  PYRATE_DATUM = 'DATUM'
  PYRATE_TIME_SPAN = 'TIME_SPAN_YEAR'
  PYRATE_WAVELENGTH_METRES = 'WAVELENGTH_METRES'
  PYRATE_INCIDENCE_DEGREES = 'INCIDENCE_DEGREES'
  PYRATE_INSAR_PROCESSOR = 'INSAR_PROCESSOR'
  PYRATE_WEATHER_ERROR = 'WEATHER_ERROR'
  PYRATE_APS_ERROR = 'APS_ERROR'
  PYRATE_MAXVAR = 'CVD_MAXVAR'
  PYRATE_ALPHA = 'CVD_ALPHA'
  COHERENCE = 'COHERENCE_MASKED_MULTILOOKED_IFG'
  MULTILOOKED = 'MULTILOOKED_IFG'
  ORIG = 'ORIGINAL_IFG'
  DEM = 'ORIGINAL_DEM'
  MLOOKED_DEM = 'MULTILOOKED_DEM'
  INCIDENCE = 'INCIDENCE_ANGLE_MAP'
  MLOOKED_INC = 'MULTILOOKED_INCIDENCE_ANGLE_MAP'
  INCR = 'INCREMENTAL_TIME_SLICE'
  CUML = 'CUMULATIVE_TIME_SLICE'
  LINRATE = 'LINEAR_RATE_MAP'
  LINERROR = 'LINEAR_RATE_ERROR_MAP'
  LINSAMP = 'LINEAR_RATE_SAMPLES'
  PYRATE_ORBITAL_ERROR = 'ORBITAL_ERROR'
  ORB_REMOVED = 'REMOVED'
  APS_REMOVED = 'REMOVED'
  PYRATE_REF_PHASE = 'REFERENCE_PHASE'
  REF_PHASE_REMOVED = 'REMOVED'
  NAN_STATUS = 'NAN_STATUS'
  NAN_CONVERTED = 'CONVERTED'
  DATA_TYPE = 'DATA_TYPE'
  DATA_UNITS = 'DATA_UNITS'
  
  DAYS_PER_YEAR = 365.25  # span of year, not a calendar year
  YEARS_PER_DAY = 1 / DAYS_PER_YEAR
  SPEED_OF_LIGHT_METRES_PER_SECOND = 3e8
  MM_PER_METRE = 1000
  