Hi Dimitris,
It is indeed hard to learn pyqgis 3 with outdated docs.
The following code worked for me (suggested by Martin Dobias):
settings = QgsMapSettings()
settings.setOutputSize(QSize(512,512))
settings.setExtent(layer.extent())
settings.setLayers([layer])
job = QgsMapRendererSequentialJob(settings)
job.start()
job.waitForFinished()
img = job.renderedImage()
img.save("/tmp/rendered.png")
When you call job.start(), it will start rendering in background and
immediately return. That's why you need to call job.waitForFinished()
to block your code until the final image is ready. This approach has a
downside that it blocks the main thread and therefore the GUI will be
blocked until rendering has finished. If you would like to avoid this
blocking, after job.start() you could have a slot that would listen to
finished() signal coming from "job" - and save the image there. This
approach makes the code a bit more complex, but the GUI does not get
blocked and you can even start multiple jobs at a time in parallel.
Hope it helps you. Good luck learning pyqgis!
Raymond
On 24-10-18 09:47, Dimitris Kar wrote:
I am trying to learn and work with PyQGIS 3.
It is a very challenging task cause documentation is really [limited and
out of date][1].
What I am trying to do is to:
1. create a project
2. add a layer
3. save the project
4. export it as a png
I have done the first 3 steps (see code below).
import sys
import qgis
from qgis.core import QgsVectorLayer
from qgis.core import QgsApplication
from qgis.core import QgsProject
from qgis.core import QgsMapRendererJob, QgsMapSettings
from qgis.gui import QgsMapCanvas
from PyQt5.QtGui import QImage, QColor, QPainter
from PyQt5.QtCore import QSize
# PYTHON APPLICATIONS
# prefix path: the location where qgis is installed in the system
# the easiest way to find the prefix path to run the following
commaand from the python console of qgis: QgsApplication.prefixPath()
#1. CREATE THE APPLICATION
QgsApplication.setPrefixPath('/usr', True)
# second parameter into false disables the gui
qgs = QgsApplication([], False)
#load providers
qgs.initQgis()
#2. CREATE THE PROJECT
# create project
project_name = '/home/dkar/workspaces/qgis/data/test_project_2.qgz'
project = QgsProject.instance()
new_project = project.write(project_name)
#3. READ/OPEN THE PROJECT
# modify the project e.g. adding more layers and save it.
new_project = project.read(project.fileName())
#4. ADD A VECTORLAYER
# add a layer in the QgsProviderRegistry
layer=QgsVectorLayer("/home/dkar/workspaces/qgis/data/pakistan_1.shp",
"pakistan", "ogr")
if not layer.isValid():
print("Layer failed")
#5. ADD LAYER TO THE REGISTRY
project.addMapLayer(layer, True)
project.write('/home/dkar/workspaces/qgis/data/test_project_2.qgz')
#6. SAVE THE PROJECT
all_layers = QgsProject.instance().mapLayers()
img = QImage(QSize (800, 600), QImage.Format_ARGB32_Premultiplied)
# set image's backgroud color
color = QColor(255, 255, 255)
img.fill(color.rgb())
#create painter
p = QPainter()
p.begin(img)
p.setRenderHint(QPainter.Antialiasing)
# THIS IS WHERE THE ISSUE APPEARS
# THIS IS WHERE THE ISSUE APPEARS
render = QgsMapRendererJob() # THIS IS WHERE THE ISSUE APPEARS
# set layer set (am I using here the prohect?)
lst = [layer.id <http://layer.id>()] # cause "layer" is the name of
the variable
render.setLayerSet(lst)
# to remove the provider and layer registries from memory
qgs.exitQgis()
But when I try to do the last part, following the instructions from the
existing documentation. I get issues because the specific function
(`QgsMapRenderer`) doesn't exist anymore in QGIS 3.
I am not sure how to solve the issue.
I see in the documentation that this function:
QgsMapRenderer
was replaced by
QgsMapRendererJob
But then when I try to import and use it in the code as:
from qgis.core import QgsMapRendererJob, QgsMapSettings
render = QgsMapRendererJob()
I get an error message:
TypeError: qgis._core.QgsMapRendererJob represents a C++ abstract
class and cannot be instantiated
Any idea how to proceed with this?
[1]:
https://docs.qgis.org/testing/pdf/en/QGIS-testing-PyQGISDeveloperCookbook-en.pdf
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