I'd like to create a Python script in QGIS that will take some data (shp + tif, in my example), use tamplate Map Composer (from a file) and export created composition to a png image.
With almost no experience in programming (less than basic Python knowledge) I google some code snippets and try to make them work together. I took the Map Composer code from some previously answered question: Save Print/Map QGIS composer view as PNG/PDF using Python (without changing anything in visible layout)?
I managed to load the data and Map Composer template (with a single map and legend items defined) but my export png image has an empty map frame (no vector/raster data within the frame). The legend item looks fine however.
Any help with making this code work?
from qgis.core import *
import qgis.utils
from PyQt4 import QtCore, QtGui
from qgis import core, gui
# ADD VECTOR LAYER
data_folder = "D:/QGIS/dane/"
granica = "granica_SZ VI_UTM34.shp"
granica_name = granica[0:-4]
granica = data_folder + granica
granica_style = "granica_style.qml"
granica_style = data_folder + granica_style
granica = iface.addVectorLayer(granica, granica_name, "ogr")
granica.loadNamedStyle(granica_style)
if not granica.isValid():
print "Granica failed to load or already loaded!"
qgis.utils.iface.legendInterface().setLayerVisible(granica, True)
# ADD RASTER LAYER
landsat = "SZ_VI_LC8-190-022_2015-111_LGN00_OLI_TIRS_atm.TIF"
landsat_name = landsat[0:-4]
landsat = data_folder + landsat
landsat_style = "landsat_style.qml"
landsat_style = data_folder + landsat_style
landsat = iface.addRasterLayer(landsat, landsat_name)
landsat.loadNamedStyle(landsat_style)
qgis.utils.iface.legendInterface().setLayerVisible(landsat, True)
iface.zoomFull()
# MOVE RASTER DOWN (change order)
canvas = qgis.utils.iface.mapCanvas()
layers = canvas.layers()
root = QgsProject.instance().layerTreeRoot()
landsat_old = root.findLayer(landsat.id())
landsat_move = landsat_old.clone()
parent = landsat_old.parent()
parent.insertChildNode(2, landsat_move)
parent.removeChildNode(landsat_old)
# USE MAP COMPOSER TEMPLATE TO EXPORT IMAGE
from qgis.gui import QgsMapCanvas, QgsLayerTreeMapCanvasBridge
from PyQt4.QtXml import QDomDocument
from PyQt4.QtGui import QImage
from PyQt4.QtGui import QPainter
from PyQt4.QtCore import QSize
template_path = data_folder + 'template.qpt'
template_file = file(template_path)
# Set output DPI
dpi = 300
canvas = QgsMapCanvas()
template_file = file(template_path)
template_content = template_file.read()
template_file.close()
document = QDomDocument()
document.setContent(template_content)
ms = canvas.mapSettings()
composition = QgsComposition(ms)
composition.loadFromTemplate(document, {})
# You must set the id in the template
map_item = composition.getComposerItemById('map')
map_item.setMapCanvas(canvas)
map_item.zoomToExtent(canvas.extent())
# You must set the id in the template
legend_item = composition.getComposerItemById('legend')
legend_item.updateLegend()
composition.refreshItems()
dpmm = dpi / 25.4
width = int(dpmm * composition.paperWidth())
height = int(dpmm * composition.paperHeight())
# create output image and initialize it
image = QImage(QSize(width, height), QImage.Format_ARGB32)
image.setDotsPerMeterX(dpmm * 1000)
image.setDotsPerMeterY(dpmm * 1000)
image.fill(0)
# render the composition
imagePainter = QPainter(image)
composition.renderPage(imagePainter, 0)
imagePainter.end()
image.save(data_folder + "out3.png", "png")
QgsApplication.exitQgis()
