Export DXF from QGIS layer using PyQGIS?

Question

I want to export a DXF file from a QGIS layer.

Sample code:

dialog = QtGui.QFileDialog()
dialog.setFileMode(QtGui.QFileDialog.Directory)
dialog.setOption(QtGui.QFileDialog.ShowDirsOnly)
DirectoryName = dialog.getExistingDirectory()
layers = self.iface.mapCanvas().layers()

for layer in layers:         
     filename = DirectoryName + "/" + layer.name() + ".dxf"    
     QgsVectorFileWriter.writeAsVectorFormat(layer, filename, "utf-8", layer.crs(), "DXF", 1)

Result DXF file is empty.

How can I export as DXF file using either QgsVectorFileWriter() or QgsDxfExport()?

Answer 1

You can take example on the code in qgisapp.cpp and transform it to python as follows (just replace the elements within underscores):

dxfExport = QgsDxfExport()

settings = iface.mapCanvas().mapSettings()
# settings.setLayerStyleOverrides( QgsProject.instance().mapThemeCollection().mapThemeStyleOverrides( _yourmaptheme_ ) )
dxfExport.setMapSettings( settings )
dxfExport.addLayers( _layers_ )
dxfExport.setSymbologyScale( _scale_ )
dxfExport.setSymbologyExport( _mode_ )
dxfExport.setLayerTitleAsName( _title_ )
dxfExport.setDestinationCrs( _crs_ )
dxfExport.setForce2d( _force2d_ )
# dxfExport.setFlags( _flags_ )
dxfExport.setExtent( _extent_ )


dxfFile = QFile( fileName )
dxfExport.writeToFile( dxfFile, _encoding_ )

addLayer was causing a crash in QGIS. It has been fixed in QGIS 2.18.17 and QGIS 3.0. _layers_ is now a list of QgsDxfExport.DxfLayer( layer )

---

Another interesting approach (although not in Python) is that you can run QGIS dxf export from the command line: qgis.exe --dxf-export file.dxf myproject.qgs

See the command line options in the QGIS documentation for a complete description.

Answer 2

If I use your code in the Python Console with the QgsVectorFileWriter() class , the value 5 is returned which seems to be a ErrAttributeCreationFailed. We could skip the attribute creation using skipAttributeCreation=True as a parameter if you don't care for the attributes.

So your final line should read:

QgsVectorFileWriter.writeAsVectorFormat(layer, filename, "utf-8", layer.crs(), "DXF", skipAttributeCreation=True)

Answer 3

Suggested solution: using the ogr library, with this approach it is possible to set the value of the "Layer" attribute of the DXF with an attribute from the inLayer.

from osgeo import ogr
import os

# Get the input Layer
inShapefile = "c://gis//wrld.shp"
inDriver = ogr.GetDriverByName("ESRI Shapefile")
inDataSource = inDriver.Open(inShapefile, 0)
inLayer = inDataSource.GetLayer()

# Create the output Layer
outDXF = "wrld.dxf"
outDriver = ogr.GetDriverByName("DXF")

# Create the output DXF
outDataSource = outDriver.CreateDataSource(outDXF)
outLayer = outDataSource.CreateLayer("wrld", geom_type=ogr.wkbPolygon)

# Add input Layer Fields to the output Layer
inLayerDefn = inLayer.GetLayerDefn()
for i in range(0, inLayerDefn.GetFieldCount()):
    fieldDefn = inLayerDefn.GetFieldDefn(i)
    outLayer.CreateField(fieldDefn)    

# Get the output Layer's Feature Definition
outLayerDefn = outLayer.GetLayerDefn()

for i in range(0, inLayer.GetFeatureCount()):
    # Get the input Feature
    inFeature = inLayer.GetFeature(i)
    # Create output Feature
    outFeature = ogr.Feature(outLayerDefn)
    # Add attribute by index from inFeature to pass to output Layer.
    # Set the field_num (here 2) by the position of the field in the original file.
    outFeature.SetField("Layer", inFeature.GetField(2))         
    # Set geometry.
    geom = inFeature.GetGeometryRef()
    outFeature.SetGeometry(geom)
    # Add new feature to output Layer
    outLayer.CreateFeature(outFeature)
    inFeature = None
    outFeature = None

# Save and close DataSources
inDataSource = None
outDataSource = None

EDIT: This can be achieved also by :

import subprocess
command = ["C:\\Program Files\\QGIS 2.14\\bin\\ogr2ogr.exe", "-f", "DXF", "output.dxf", "c:\\gis\\wrld.shp", "-sql", "select ISO as Layer from wrld"]
subprocess.check_call(command)

For lines use:

import subprocess
command = ["C:\\Program Files\\QGIS 2.14\\bin\\ogr2ogr.exe", "-f", "DXF", "output_l.dxf", "c:\\gis\\wrld.shp", "-sql", "select ISO as Layer from wrld", "-nlt", "MULTILINESTRING"]
subprocess.check_call(command)

[Note: ISO is a name of a field in wrld.shp]