Create static map images via QGIS.

qgis_map_imaging.py

"""
Script to use for creating static map images in QGIS. 
A dictionary of bounding boxes is required, with key representing the 
linkId and value a list of four coordinates representing the region that 
encloses the link. The dictionary for Charlotte has been included in the 
repository.

Author: James D. Triveri
Date: 2024-02
"""

from math import radians, sin, asin, cos, sqrt, pi, log, tan
import os
from pathlib import Path
import pickle
import sys
import time
import numpy as np
import qgis.utils
from qgis.core import (
    QgsGeometry, QgsMapSettings, QgsPrintLayout, QgsMapSettings, 
    QgsMapRendererParallelJob, QgsLayoutItemLabel, QgsLayoutItemLegend, 
    QgsLayoutItemMap, QgsLayoutItemPolygon, QgsLayoutItemScaleBar, 
    QgsLayoutExporter, QgsLayoutItem, QgsLayoutPoint, QgsLayoutSize, 
    QgsUnitTypes, QgsProject, QgsFillSymbol
    )
from qgis.PyQt.QtGui import QPolygonF, QColor
from qgis.PyQt.QtCore import QPointF, QRectF, QSize
from qgis.PyQt.QtCore import QEventLoop

# Configuration ----------------------------------------------------------------

img_basis = 256
tiles = "osm"
m = .0000005
bboxes_path = "charlotte-linkid-bboxes.pkl"
output_dirname = f"charlotte-linkid-images/{tiles}-{img_basis}"


# Declarations -----------------------------------------------------------------

def convert(lat: float, lon: float):
    """
    Convert lat-lon pair into EPSG:3857 representation.
    """
    x = (lon * 20037508.34 / 180.)
    y = ((log(tan(((90. + lat) * pi) / 360)) / (pi / 180)) * 20037508.34) / 180
    return((y, x))

# ------------------------------------------------------------------------------

# Create output directory. 
output_dir = Path(output_dirname)
if not output_dir.exists():
    os.makedirs(output_dir)

# Load linkId bounding coordinates.
with open(bboxes_path, "rb") as fpkl:
    dparts = pickle.load(fpkl)

# Bind reference to layers.
layers = iface.mapCanvas().layers()


nbr_links = len(dparts)

for indx, link_id in enumerate(dparts, start=1):

    dbbox = dparts[link_id]
    
    img_path = output_dir.joinpath(f"{link_id}.png")
    
    if not img_path.exists():
    
        lat0, lon0, lat1, lon1 = dbbox["lat0"], dbbox["lon0"], dbbox["lat1"], dbbox["lon1"]
        lat0 = (1 - m) * lat0
        lon0 = (1 + m) * lon0
        lat1 = (1 + m) * lat1
        lon1 = (1 - m) * lon1
        
        img_h = img_basis
        img_w = img_basis
        
        ymin, xmin = convert(lat0, lon0)
        ymax, xmax = convert(lat1, lon1)
        bbox = QgsRectangle(xmin, ymin, xmax, ymax)
        settings = QgsMapSettings()
        settings.setOutputSize(QSize(img_w, img_h))
        settings.setLayers(layers)
        settings.setBackgroundColor(QColor(255, 255, 255))
        settings.setOutputSize(QSize(img_w, img_h))
        settings.setExtent(bbox)
        settings.visibleExtent()
        render = QgsMapRendererParallelJob(settings)

        def _finished():
            img = render.renderedImage()
            img.save(str(img_path), "png")

        render.finished.connect(_finished)
        render.start()
        loop = QEventLoop()
        render.finished.connect(loop.quit)
        loop.exec_()
        print(f"[{indx}-of-{nbr_links}] Created {img_path}.")