qgis_wkt_extraction.py

"""A collection of functions to extract WKT from selected features."""

from qgis.core import (
    Qgis,
    QgsCoordinateReferenceSystem,
    QgsCoordinateTransform,
    QgsProject,
)
from qgis.utils import iface


def get_wkt_of_selected_feature(precision=4):
    """Returns the WKT of the first selected polygon in WGS84."""

    # grab the active layer and the list of selected features in this layer
    active_layer = iface.activeLayer()
    selected_features = active_layer.selectedFeatures()

    # if none are selected, show a message and return
    if len(selected_features) == 0:
        iface.messageBar().pushMessage(
            "Error",
            "No features selected",
            level=Qgis.Critical,
            duration=3,
        )
        return

    # if there are selected features, grab the first and extract the geometry
    selected_feature = selected_features[0]
    geometry = selected_feature.geometry()

    # reproject to WGS84 if active layer has a different CRS
    source_crs = active_layer.crs()
    if source_crs.authid() != "EPSG:4326":
        # the QgsCoordinateTransform needs the project for some reason
        project = QgsProject.instance()
        target_crs = QgsCoordinateReferenceSystem("EPSG:4326")
        transform = QgsCoordinateTransform(source_crs, target_crs, project)

        geometry.transform(transform)

    return geometry.asWkt(precision=precision)