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() 
