QGIS function to create dynamic map grids

map_grids.py

"""
Define new functions using @qgsfunction. feature and parent must always be the
last args. Use args=-1 to pass a list of values as arguments
"""

from qgis.core import Qgis, QgsProject,QgsCoordinateTransform,QgsCoordinateReferenceSystem
from qgis.gui import *
from qgis.utils import qgsfunction, iface

def map_bounds(composer_title, map_id):
    projectInstance = QgsProject.instance()
    projectLayoutManager = projectInstance.layoutManager()
    layout = projectLayoutManager.layoutByName(composer_title)
    map=layout.itemById(map_id)
    transform = QgsCoordinateTransform(QgsCoordinateReferenceSystem("EPSG:3857"),QgsCoordinateReferenceSystem("EPSG:4326"),projectInstance )
    bbox= map.extent()
    extent=transform.transformBoundingBox(bbox)
    return extent

@qgsfunction(args='auto', group='Custom')
def map_x_min(composer_title, map_id, feature, parent):
    """
    Calculates the map_x_min of the map layout.
    <h2>Example usage:</h2>
    <ul>
      <li>map_x_min(composer_title, map_id) </li>
       <li>map_x_min('sample_map', 'main') </li>
    </ul>
    """
    map_extent = map_bounds(composer_title, map_id)
    x_min = map_extent.xMinimum()
    return x_min
    
@qgsfunction(args='auto', group='Custom')
def map_x_max(composer_title, map_id, feature, parent):
    """
    Calculates the map_x_min of the map layout.
    <h2>Example usage:</h2>
    <ul>
      <li>map_x_max(composer_title, map_id) </li>
       <li>map_x_max('sample_map', 'main') </li>
    </ul>
    """
    map_extent = map_bounds(composer_title, map_id)
    x_max = map_extent.xMaximum()
    return x_max
    
@qgsfunction(args='auto', group='Custom')
def map_y_min(composer_title, map_id, feature, parent):
    """
    Calculates the map_x_min of the map layout.
    <h2>Example usage:</h2>
    <ul>
      <li>map_y_min(composer_title, map_id) </li>
       <li>map_y_min('sample_map', 'main') </li>
    </ul>
    """
    map_extent = map_bounds(composer_title, map_id)
    y_min = map_extent.yMinimum()
    return y_min
    
@qgsfunction(args='auto', group='Custom')
def map_y_max(composer_title, map_id, feature, parent):
    """
    Calculates the map_x_min of the map layout.
    <h2>Example usage:</h2>
    <ul>
      <li>map_y_max(composer_title, map_id) </li>
       <li>map_y_max('sample_map', 'main') </li>
    </ul>
    """
    map_extent = map_bounds(composer_title, map_id)
    y_max = map_extent.yMaximum()
    return y_max