The MapGenerator Class

API docs

Each map type of an autoMaps project needs to consist of:

• a MapType object (see this section)
• a generator class (a subclass of MapGenerator), described here
• one or more QGIS print layouts in an associated QGIS project file (see this section)

Each generator class needs to be a subclass of automaps.generators.base.MapGenerator.

Each generator class needs a class attribute name, a method _set_steps(), and freely definable methods for map generation.

The method _set_steps() must itself set the attribute self.steps of type OrderedDict[str, Step].

As keys of the OrderedDict, speaking names of the processing step should be assigned. These are also displayed in the frontend for information about the processing progress. The processing is carried out in the ordered of the items in the OrderedDict.

As values of the OrderedDict, NamedTuples of type Step are expected, with the following attributes:

• func (Callable) is the method defined in the class that executes the step.
• weight (float) is the relative weight of the step with respect to the expected processing time (relative to the other steps).This is used to display the progress bar in the frontend.

Info

For each execution of a step a new instance of the MapGenerator is created! The attribute self can therefore not be used to pass data between steps. Instead, the attribute step_data of type StepData should be used (take a look at the example below). For this purpose, attributes can be added freely to the step_data object.

During initialization, the associated QGIS project (defined with the config option FILEPATH_QGIS_PROJECT) and the print layout (defined with the argument print_layout). in the configuration of the associated MapType in /automapsconf.py) are loaded. These to objects are stored in self.step_data.project and self.step_data.layout, respectively, and are thus available for all processing steps.

For example, a small generator class with four steps could look like this:

from collections import OrderedDict

from automaps.generators.base import MapGenerator, Step


class MapGeneratorPoly(MapGenerator):
    name = "Districts in Vienna"

    def _set_steps(self):
        self.steps = OrderedDict(
            {
                "Initialize project": Step(self.init_project, 1),
                "Filter layers": Step(self.filter_layers, 1),
                "Zoom to extent": Step(self.set_extent, 1),
                "Export map": Step(self.export_layout, 5),
            }
        )

    def init_project(self):
        self._init_layers()
        self._set_project_variable("data", self.data)
        self._set_map_layer_visibility("districts", True)
        self._set_map_layer_visibility("OpenStreetMap", True)
        self.step_data.district_filter = f"NAMEK = '{self.data['District name']}'"

    def filter_layers(self):
        self._set_map_layer_filter_expression(
            "districts", self.step_data.district_filter
        )

    def set_extent(self):
        self._zoom_map_to_layer_extent("Map 1", self._get_map_layer("districts"))

    def export_layout(self):
        self._export_print_layout()
        self.step_data.project.write("./poly_out.qgz")
        del self.step_data.project

The MapGenerator base class offers many helper methods to simplify the calls to the QGIS API, e.g. to set filter expressions, set map extents, set project variables, or toggle the visibility of layers. Take a look at the API documentation for further details.