compactness_calculator.py

# -*- coding: utf-8 -*-
"""
/***************************************************************************
 CompactnessCalculator
                                 A QGIS plugin
 Compactness calculations
                              -------------------
        begin                : 2017-08-10
        git sha              : $Format:%H$
        copyright            : (C) 2017 by Ariel and Vanessa
        email                : vanessa@flippable.org
 ***************************************************************************/

/***************************************************************************
 *                                                                         *
 *   This program is free software; you can redistribute it and/or modify  *
 *   it under the terms of the GNU General Public License as published by  *
 *   the Free Software Foundation; either version 2 of the License, or     *
 *   (at your option) any later version.                                   *
 *                                                                         *
 ***************************************************************************/
"""
import json
import os.path
from PyQt4.QtCore import (QSettings, QTranslator, qVersion, QCoreApplication,
                          QVariant, QObject, SIGNAL)
from PyQt4.QtGui import QAction, QIcon, QMessageBox
from qgis.core import (QgsCoordinateTransform, QgsCoordinateReferenceSystem,
                       QgsVectorLayer, QgsField,
                       QgsMapLayerRegistry, QgsVectorFileWriter)
# Initialize Qt resources from file resources.py
import resources
# Import the code for the dialog
from compactness_calculator_dialog import CompactnessCalculatorDialog
from mander import districts, metrics

# TODO Check file against pylint
# TODO Diagram
class CompactnessCalculator:
    """QGIS Plugin Implementation."""

    def __init__(self, iface):
        """Constructor.

        :param iface: An interface instance that will be passed to this class
            which provides the hook by which you can manipulate the QGIS
            application at run time.
        :type iface: QgsInterface
        """
        # Save reference to the QGIS interface
        self.iface = iface
        # initialize plugin directory
        self.plugin_dir = os.path.dirname(__file__)
        # initialize locale
        locale = QSettings().value('locale/userLocale')[0:2]
        locale_path = os.path.join(
            self.plugin_dir,
            'i18n',
            'CompactnessCalculator_{}.qm'.format(locale))

        if os.path.exists(locale_path):
            self.translator = QTranslator()
            self.translator.load(locale_path)

            if qVersion() > '4.3.3':
                QCoreApplication.installTranslator(self.translator)


        # Declare instance attributes
        self.actions = []
        self.menu = self.tr(u'&Compactness Calculator')
        # TODO: We are going to let the user set this up in a future iteration
        self.toolbar = self.iface.addToolBar(u'CompactnessCalculator')
        self.toolbar.setObjectName(u'CompactnessCalculator')

    # noinspection PyMethodMayBeStatic
    def tr(self, message):
        """Get the translation for a string using Qt translation API.

        We implement this ourselves since we do not inherit QObject.

        :param message: String for translation.
        :type message: str, QString

        :returns: Translated version of message.
        :rtype: QString
        """
        # noinspection PyTypeChecker,PyArgumentList,PyCallByClass
        return QCoreApplication.translate('CompactnessCalculator', message)


    def add_action(
        self,
        icon_path,
        text,
        callback,
        enabled_flag=True,
        add_to_menu=True,
        add_to_toolbar=True,
        status_tip=None,
        whats_this=None,
        parent=None):
        """Add a toolbar icon to the toolbar.

        :param icon_path: Path to the icon for this action. Can be a resource
            path (e.g. ':/plugins/foo/bar.png') or a normal file system path.
        :type icon_path: str

        :param text: Text that should be shown in menu items for this action.
        :type text: str

        :param callback: Function to be called when the action is triggered.
        :type callback: function

        :param enabled_flag: A flag indicating if the action should be enabled
            by default. Defaults to True.
        :type enabled_flag: bool

        :param add_to_menu: Flag indicating whether the action should also
            be added to the menu. Defaults to True.
        :type add_to_menu: bool

        :param add_to_toolbar: Flag indicating whether the action should also
            be added to the toolbar. Defaults to True.
        :type add_to_toolbar: bool

        :param status_tip: Optional text to show in a popup when mouse pointer
            hovers over the action.
        :type status_tip: str

        :param parent: Parent widget for the new action. Defaults None.
        :type parent: QWidget

        :param whats_this: Optional text to show in the status bar when the
            mouse pointer hovers over the action.

        :returns: The action that was created. Note that the action is also
            added to self.actions list.
        :rtype: QAction
        """

        # Create the dialog (after translation) and keep reference
        self.dlg = CompactnessCalculatorDialog()

        icon = QIcon(icon_path)
        action = QAction(icon, text, parent)
        action.triggered.connect(callback)
        action.setEnabled(enabled_flag)

        if status_tip is not None:
            action.setStatusTip(status_tip)

        if whats_this is not None:
            action.setWhatsThis(whats_this)

        if add_to_toolbar:
            self.toolbar.addAction(action)

        if add_to_menu:
            self.iface.addPluginToVectorMenu(
                self.menu,
                action)

        self.actions.append(action)

        return action

    def initGui(self):
        """Create the menu entries and toolbar icons inside the QGIS GUI."""

        icon_path = ':/plugins/CompactnessCalculator/icon.png'
        self.add_action(
            icon_path,
            text=self.tr(u'Compactness Calculations'),
            callback=self.run,
            parent=self.iface.mainWindow())

        QObject.connect(self.dlg.ConvexHull, SIGNAL("currentIndexChanged(int)"), self.populate)
        QObject.connect(self.dlg.Polsby, SIGNAL("currentIndexChanged(int)"), self.populate)
        QObject.connect(self.dlg.Reock, SIGNAL("currentIndexChanged(int)"), self.populate)
        QObject.connect(self.dlg.Schwartzberg, SIGNAL("currentIndexChanged(int)"), self.populate)


    def unload(self):
        """Removes the plugin menu item and icon from QGIS GUI."""
        for action in self.actions:
            self.iface.removePluginVectorMenu(
                self.tr(u'&Compactness Calculator'),
                action)
            self.iface.removeToolBarIcon(action)
        # remove the toolbar
        del self.toolbar


    def get_current_selection(self):
        """Returns the features currently selected by the user."""
        layer = self.iface.activeLayer()

        if not layer:
            QMessageBox.critical(self.dlg, 'Error', u"Please select a layer!")
            return False

        self.crs = layer.crs()

        if layer.selectedFeatures() == []:
            QMessageBox.warning(self.dlg,
                                 'Warning',
                                 u"No features selected - the entire layer will be processed.")
            layer.selectAll()
        self.features = layer.selectedFeatures()
        return True

    def features_to_geojson(self):
        """Converts a qgis Feature geometry to GeoJSON format."""
        # Coordinate transform -> EPSG 4326
        target_crs = QgsCoordinateReferenceSystem(4326, QgsCoordinateReferenceSystem.EpsgCrsId)
        if not target_crs.isValid():
            QMessageBox.critical(self.dlg, 'Error', u"Error creating target CRS.")
            return False

        xform = QgsCoordinateTransform(self.crs, target_crs)

        geojson_features = []
        for f in self.features:
            geom = f.geometry()
            """ Access relevant params. Could be useful in future.
            self.perimeter = geom.length()
            self.area = geom.area()
            self.convex_hull_area = geom.convexHull().area()
            # We can't calculate minimum bounding circle easily in QGIS.
            # Can we maybe calculate largest distance from centroid to edge?
            """
            if geom.transform(xform) != 0:
                QMessageBox.critical(self.dlg, 'Error', u"Error transforming CRS.")
                return False

            geojson_features.append({'geometry': json.loads(geom.exportToGeoJSON()),
                                     'properties': {},
                                     'type': 'Feature'})

        self.geojson = {'type': 'FeatureCollection',
                        'features': geojson_features}
        return True

    def calc_scores(self, mets):
        """Calculates compactness metrics for the geoms using mander."""
        d = districts.District(json=self.geojson)
        self.scores = {}
        for metric in mets:
            if metric == "PP":
                self.scores[metric] = metrics.calculatePolsbyPopper(d).tolist()
            elif metric == "CH":
                self.scores[metric] = metrics.calculateConvexHull(d).tolist()
            elif metric == "RK":
                self.scores[metric] = metrics.calculateReock(d).tolist()
            elif metric == "SB":
                self.scores[metric] = metrics.calculateSchwartzberg(d).tolist()
        return True

    def generate_layer(self, layer=True, path=None):
        """Creates an in-memory layer and displays/saves it."""
        # Create a new layer in memory
        new_layer = QgsVectorLayer('Polygon', "compactness_scores", "memory")
        provider = new_layer.dataProvider()

        # Add the new fields
        new_fields = sorted(self.scores.keys())  # need the same order every time
        fields = self.features[0].fields()  # QgsFields object
        for field in new_fields:
            fields.append(QgsField(field, QVariant.Double, '', 20, 4))

        # All changes to the layer happen below
        new_layer.startEditing()

        # Set layer CRS
        # NOTE A warning message will still appear in QGIS
        # because this isn't set at layer creation time.
        new_layer.setCrs(self.crs)

        # Set layer attributes (fields)
        provider.addAttributes(fields.toList())
        new_layer.updateFields()

        # Update features with new data
        for i in xrange(0, len(self.features)):
            attributes = self.features[i].attributes()  # list of values
            for field in new_fields:
                attributes.append(float(self.scores[field][i]))
            self.features[i].setAttributes(attributes)

        # Add features
        provider.addFeatures(self.features)

        new_layer.commitChanges()
        new_layer.updateExtents()

        if path.strip() != "":
            if path.endswith(".json") or path.endswith(".geojson"):
                filetype = 'GeoJson'
            elif path.endswith(".shp"):
                filetype = 'ESRI Shapefile'
            else:
                QMessageBox.critical(self.dlg,
                                     'Error',
                                     u"Unsupported file type. Only GeoJSON (.json, .geojson) and ESRI Shapefile (.shp) are supported.")
                return False

            QgsVectorFileWriter.writeAsVectorFormat(new_layer,
                                                    path,
                                                    'utf-8',
                                                    new_layer.crs(),
                                                    filetype)
            print "Saved to " + path

        if layer:
            QgsMapLayerRegistry.instance().addMapLayer(new_layer)

        return True

    def run(self):
        """Run method that performs all the real work."""
        if not self.get_current_selection():
            return

        # show the dialog
        self.dlg.show()
        # Run the dialog event loop
        result = self.dlg.exec_()
        self.populate()
        # See if OK was pressed
        if result:
            self.features_to_geojson()
            if not isinstance(self.geojson, dict):
                QMessageBox.critical(self.dlg, 'Error', u"GeoJSON wasn't formed properly.")
                return

            # Get desired metrics from dialog
            # TODO populate dialog with available metrics from mander
            mets = []
            if self.dlg.Polsby.isChecked():
                mets.append("PP")
            if self.dlg.ConvexHull.isChecked():
                mets.append("CH")
            if self.dlg.Reock.isChecked():
                mets.append("RK")
            if self.dlg.Schwartzberg.isChecked():
                mets.append("SB")

            if mets == []:
                QMessageBox.warning(self.dlg, 'Warning', u"Please select at least one metric.")
                self.dlg.show()

            if not self.calc_scores(mets):
                QMessageBox.critical(self.dlg, 'Error', u"Error calculating scores.")
                return

            if not self.generate_layer(layer=self.dlg.layerFlag.isChecked(),
                                       path=self.dlg.filepath.text()):
                QMessageBox.critical(self.dlg, 'Error', u"Error adding layer or saving file.")
                return
            return

    def populate(self):
        """May be useful for more complicated UI functionality."""
        pass