I wrote a script to create a big number of heat maps for a given scenario. I would like to save the result of every heat map as an PNG image. I have figured it out doing it with simple Map Rendering but the quality of the result is too low. Furthermore I would like to export to OpenLayers using the same code, which does not seem to be possible with simple rendering.
Now I am trying to do it with QgsComposition instead. Manually in the Map Composer you can just set the paper color to transparent and disable the background of the map canvas.
This is the code that I have so far. I just cannot figure out why it is not working. The result png-file always has a white opaque background.
My OS is Windows 7 and I'm using QGIS 2.6 Brighton.
I hope someone can help me out here.
# PARAMETERS mainPath = 'path/to/folder/' filename = 'filename' imageType = "png" imageWidth_mm = 400 imageHeight_mm = 160 dpi = 300 mapRenderer = iface.mapCanvas().mapRenderer() c = QgsComposition(mapRenderer) c.setPlotStyle(QgsComposition.Print) c.setPaperSize(400, 160) x, y = 0, 0 w, h = c.paperWidth(), c.paperHeight() composerMap = QgsComposerMap(c, x ,y, w, h) c.addItem(composerMap) # get all items and disable the backgrounds itemList = c.items() c.removeItem(itemList) c.removeItem(itemList) itemList.setBackgroundEnabled(False) itemList.setBackgroundEnabled(False) # add them to the composition c.addItem(itemList) c.addItem(itemList) c.refreshItems() c.refreshDataDefinedProperty(QgsComposerObject.AllProperties) c.setPrintResolution(dpi) dpmm = dpi / 25.4 width = int(dpmm * c.paperWidth()) height = int(dpmm * c.paperHeight()) # create output image and initialize it # image = QImage(QSize(width, height), QImage.Format_ARGB32) image = QImage(QSize(width, height), QImage.Format_ARGB32_Premultiplied) image.setDotsPerMeterX(dpmm * 1000) image.setDotsPerMeterY(dpmm * 1000) #image.fill(0) imagePainter = QPainter(image) # This part does not seem to have any effect #brush = QBrush(Qt.BrushStyle(0)) # transparent brush # #imagePainter.setBackgroundMode(0) #c.setBackgroundBrush(brush) c.renderPage( imagePainter, 0 ) imagePainter.end() imageFilename = mainPath + filename + '.' + imageType image.save(imageFilename, imageType) print 'image saved' print 'done'