Unable to export map with pyQGIS3

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I am trying to learn and work with pyQGIS3. It's a very challenging task because documentation is really limited and out of date.

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()] # 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 QGIS3. 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 and use it in the code as:

from qgis.core import QgsMapRendererJob, QgsMapSettings
 render = QgsMapRendererJob()

I get the error message:

TypeError: qgis._core.QgsMapRendererJob represents a C++ abstract class and cannot be instantiated

Any idea how to proceed with this?

qgis python pyqgis-3

share|improve this question

edited 14 mins ago

lambertj

1,5431421

asked 1 hour ago

user1919

1,13811031

add a comment | 

up vote
1
down vote

favorite

I am trying to learn and work with pyQGIS3. It's a very challenging task because documentation is really limited and out of date.

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()] # 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 QGIS3. 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 and use it in the code as:

from qgis.core import QgsMapRendererJob, QgsMapSettings
 render = QgsMapRendererJob()

I get the error message:

TypeError: qgis._core.QgsMapRendererJob represents a C++ abstract class and cannot be instantiated

Any idea how to proceed with this?

qgis python pyqgis-3

share|improve this question

edited 14 mins ago

lambertj

1,5431421

asked 1 hour ago

user1919

1,13811031

add a comment | 

up vote
1
down vote

favorite

up vote
1
down vote

favorite

I am trying to learn and work with pyQGIS3. It's a very challenging task because documentation is really limited and out of date.

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()] # 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 QGIS3. 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 and use it in the code as:

from qgis.core import QgsMapRendererJob, QgsMapSettings
 render = QgsMapRendererJob()

I get the error message:

TypeError: qgis._core.QgsMapRendererJob represents a C++ abstract class and cannot be instantiated

Any idea how to proceed with this?

qgis python pyqgis-3

share|improve this question

edited 14 mins ago

lambertj

1,5431421

asked 1 hour ago

user1919

1,13811031

I am trying to learn and work with pyQGIS3. It's a very challenging task because documentation is really limited and out of date.

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()] # 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 QGIS3. 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 and use it in the code as:

from qgis.core import QgsMapRendererJob, QgsMapSettings
 render = QgsMapRendererJob()

I get the error message:

TypeError: qgis._core.QgsMapRendererJob represents a C++ abstract class and cannot be instantiated

Any idea how to proceed with this?

qgis python pyqgis-3

qgis python pyqgis-3

share|improve this question

edited 14 mins ago

lambertj

1,5431421

asked 1 hour ago

user1919

1,13811031

share|improve this question

edited 14 mins ago

lambertj

1,5431421

asked 1 hour ago

user1919

1,13811031

share|improve this question

share|improve this question

edited 14 mins ago

lambertj

1,5431421

edited 14 mins ago

lambertj

1,5431421

edited 14 mins ago

lambertj

1,5431421

1,5431421

asked 1 hour ago

user1919

1,13811031

asked 1 hour ago

user1919

1,13811031

asked 1 hour ago

user1919

1,13811031

1,13811031

add a comment | 

add a comment | 

1 Answer
1

active

oldest

votes

up vote
3
down vote

Well, the error message is correct. According to the QGIS API documentation, QgsMapRendererJob is an abstract class. So you cannot directly use it. Instead you need to use one of the subclasses:

QgsMapRendererSequentialJob - renders map in one background thread to an image
QgsMapRendererParallelJob - renders map in multiple background threads to an image
QgsMapRendererCustomPainterJob - renders map with given QPainter in one background thread

https://www.qgis.org/api/classQgsMapRendererJob.html#details

share|improve this answer

answered 1 hour ago

Thomas

1,287416

add a comment | 

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1 Answer
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1 Answer
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oldest

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active

oldest

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oldest

votes

up vote
3
down vote

Well, the error message is correct. According to the QGIS API documentation, QgsMapRendererJob is an abstract class. So you cannot directly use it. Instead you need to use one of the subclasses:

QgsMapRendererSequentialJob - renders map in one background thread to an image
QgsMapRendererParallelJob - renders map in multiple background threads to an image
QgsMapRendererCustomPainterJob - renders map with given QPainter in one background thread

https://www.qgis.org/api/classQgsMapRendererJob.html#details

share|improve this answer

answered 1 hour ago

Thomas

1,287416

add a comment | 

up vote
3
down vote

Well, the error message is correct. According to the QGIS API documentation, QgsMapRendererJob is an abstract class. So you cannot directly use it. Instead you need to use one of the subclasses:

QgsMapRendererSequentialJob - renders map in one background thread to an image
QgsMapRendererParallelJob - renders map in multiple background threads to an image
QgsMapRendererCustomPainterJob - renders map with given QPainter in one background thread

https://www.qgis.org/api/classQgsMapRendererJob.html#details

share|improve this answer

answered 1 hour ago

Thomas

1,287416

add a comment | 

up vote
3
down vote

up vote
3
down vote

Well, the error message is correct. According to the QGIS API documentation, QgsMapRendererJob is an abstract class. So you cannot directly use it. Instead you need to use one of the subclasses:

QgsMapRendererSequentialJob - renders map in one background thread to an image
QgsMapRendererParallelJob - renders map in multiple background threads to an image
QgsMapRendererCustomPainterJob - renders map with given QPainter in one background thread

https://www.qgis.org/api/classQgsMapRendererJob.html#details

share|improve this answer

answered 1 hour ago

Thomas

1,287416

Well, the error message is correct. According to the QGIS API documentation, QgsMapRendererJob is an abstract class. So you cannot directly use it. Instead you need to use one of the subclasses:

QgsMapRendererSequentialJob - renders map in one background thread to an image
QgsMapRendererParallelJob - renders map in multiple background threads to an image
QgsMapRendererCustomPainterJob - renders map with given QPainter in one background thread

https://www.qgis.org/api/classQgsMapRendererJob.html#details

share|improve this answer

answered 1 hour ago

Thomas

1,287416

share|improve this answer

share|improve this answer

answered 1 hour ago

Thomas

1,287416

answered 1 hour ago

Thomas

1,287416

answered 1 hour ago

Thomas

1,287416

1,287416

add a comment | 

add a comment | 

 

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