mtl_gis_oo/scrub_layer_class.py

from qgis.core import QgsApplication, QgsField, QgsProject, \
  QgsProcessingFeedback, QgsVectorLayer, QgsVectorDataProvider, \
  QgsExpressionContext, QgsExpressionContextUtils, edit
from qgis.PyQt.QtCore import QVariant
from qgis.analysis import QgsNativeAlgorithms
from basic_functions import *
import processing


class ScrubLayer:
  def __init__(self, qgis_path, layer_path, layer_name):
    # Set the path to QGIS installation
    QgsApplication.setPrefixPath(qgis_path, True)

    # Initialize QGIS application
    qgs = QgsApplication([], False)
    qgs.initQgis()

    self.layer_path = layer_path
    self.layer_name = layer_name
    self.layer = self.load_layer()
    self.data_count = self.layer.featureCount()

  def load_layer(self):
    the_layer = QgsVectorLayer(self.layer_path, self.layer_name, 'ogr')
    if not the_layer.isValid():
      raise ValueError(f'Failed to load layer {self.layer_name} from {self.layer_path}')
    else:
      QgsProject.instance().addMapLayer(the_layer)
    return the_layer

  def fix_geometries(self, fixed_layer):
    QgsApplication.processingRegistry().addProvider(QgsNativeAlgorithms())
    fix_geometries_params = {
      'INPUT': self.layer,
      'METHOD': 0,
      'OUTPUT': fixed_layer
    }
    processing.run("native:fixgeometries", fix_geometries_params)

  def create_spatial_index(self):
    QgsApplication.processingRegistry().addProvider(QgsNativeAlgorithms())
    create_spatial_index_params = {
      'INPUT': self.layer,
      'OUTPUT': 'Output'
    }
    processing.run("native:createspatialindex", create_spatial_index_params)
    print(f'Creating Spatial index for {self.layer_name} is completed.')

  def spatial_join(self, joining_layer_path, joined_layer_path):
    """In QGIS, it is called 'Join attributes by Location'"""
    params = {'INPUT': self.layer,
              'PREDICATE': [0],
              'JOIN': joining_layer_path,
              'JOIN_FIELDS': [],
              'METHOD': 0,
              'DISCARD_NONMATCHING': False,
              'PREFIX': '',
              'OUTPUT': joined_layer_path}

    feedback = QgsProcessingFeedback()
    processing.run('native:joinattributesbylocation', params, feedback=feedback)
    print(f'Spatial Join with input layer {self.layer_name} is completed.')

  def clip_layer(self, overlay_layer, clipped_layer):
    """This must be tested"""
    QgsApplication.processingRegistry().addProvider(QgsNativeAlgorithms())
    clip_layer_params = {
      'INPUT': self.layer_path,
      'OVERLAY': overlay_layer,
      'FILTER_EXPRESSION': '',
      'FILTER_EXTENT': None,
      'OUTPUT': clipped_layer
    }
    processing.run("native:clip", clip_layer_params)
    print(f'Clipping of {self.layer_name} is completed.')

  def multipart_to_singleparts(self, singleparts_layer_path):
    QgsApplication.processingRegistry().addProvider(QgsNativeAlgorithms())
    params = {'INPUT': self.layer,
              'OUTPUT': singleparts_layer_path}
    processing.run("native:multiparttosingleparts", params)

  def split_layer(self, number_of_layers, splitted_layers_dir, app_path):
    number_of_layers -= 1
    QgsApplication.processingRegistry().addProvider(QgsNativeAlgorithms())
    create_folders(splitted_layers_dir, number_of_layers)
    intervals = self.data_count // number_of_layers
    for part in range(number_of_layers):
      output_layer_path = \
        splitted_layers_dir + f'/layer_{part}/layer_{part}.shp'
      params = {'INPUT': self.layer,
                'EXPRESSION': f'$id >= {part * intervals} '
                              f'AND $id < {(part + 1) * intervals}\r\n',
                'OUTPUT': output_layer_path}

      processing.run("native:extractbyexpression", params)

      new_layer = ScrubLayer(app_path, output_layer_path, 'Temp Layer')
      new_layer.create_spatial_index()

    remaining_features = number_of_layers
    os.makedirs(splitted_layers_dir + f'/layer_{remaining_features}')
    output_layer_path = splitted_layers_dir + \
        f'/layer_{remaining_features}/layer_{remaining_features}.shp'
    params = {'INPUT': self.layer,
              'EXPRESSION': f'$id >= {number_of_layers * intervals}\r\n',
              'OUTPUT': output_layer_path}

    processing.run("native:extractbyexpression", params)
    new_layer = ScrubLayer(app_path, output_layer_path, 'Temp Layer')
    new_layer.create_spatial_index()

  def delete_duplicates(self, deleted_duplicates_layer):
    QgsApplication.processingRegistry().addProvider(QgsNativeAlgorithms())
    params = {'INPUT': self.layer_path,
              'OUTPUT': deleted_duplicates_layer}
    processing.run("native:deleteduplicategeometries", params)

  def delete_field(self, field_name):
    QgsApplication.processingRegistry().addProvider(QgsNativeAlgorithms())
    with edit(self.layer):
      # Get the index of the column to delete
      idx = self.layer.fields().indexFromName(field_name)

      # Delete the field
      self.layer.deleteAttribute(idx)

      # Update layer fields
      self.layer.updateFields()

  def add_field(self, new_field_name):
    functionalities = self.layer.dataProvider().capabilities()

    if functionalities & QgsVectorDataProvider.AddAttributes:
      new_field = QgsField(new_field_name, QVariant.Double)
      self.layer.dataProvider().addAttributes([new_field])
      self.layer.updateFields()

  def assign_area(self, field_name):
    self.layer.startEditing()
    idx = self.layer.fields().indexFromName(field_name)

    context = QgsExpressionContext()
    context.appendScopes(QgsExpressionContextUtils.globalProjectLayerScopes(self.layer))

    for feature in self.layer.getFeatures():
      area = feature.geometry().area()
      feature[idx] = area
      self.layer.updateFeature(feature)

    self.layer.commitChanges()

  def __str__(self):
    return f'The {self.layer_name} has {self.data_count} records.'

  @staticmethod
  def cleanup():
    QgsApplication.exitQgis()