Geographic Information Systems Asked by Zhifang Hu on June 10, 2021
I am trying to create contours from a raster layer I have loaded in my QGIS project as below using gdal
from qgis.core import QgsProject
import processing
## QgsVectorLayer('Coordinate','Layer name','memory layer')
layer = QgsVectorLayer('LineString?crs=epsg:28356', 'Contour' , 'memory')
for raster in QgsProject.instance().mapLayers().values():
if 'h_Max' in raster.name():
processing.run('gdal:contour', raster, 1, 'ELEV' , layer)
I’ve never had any chance of getting the code to work, the error message I got is
AttributeError: 'QgsVectorLayer' object has no attribute 'feedback'
I am not sure when I should define this feedback attribute, any suggestion?
You need to pass the algorithm parameters as a dictionary.
Try something like:
raster = [l for l in QgsProject().instance().mapLayers().values() if isinstance(l, QgsRasterLayer) and 'h_Max' in l.name()][0]
processing.runAndLoadResults("gdal:contour",
{'INPUT':raster,
'BAND':1,
'INTERVAL':10,# adjust interval as required
'FIELD_NAME':'ELEV',
'OUTPUT':'TEMPORARY_OUTPUT'})
By executing processing.algorithmHelp("gdal:contour") you may also get additional information about the algorithm:
Contour (gdal:contour)
----------------
Input parameters
----------------
INPUT: Input layer
Parameter type: QgsProcessingParameterRasterLayer
Accepted data types:
- str: layer ID
- str: layer name
- str: layer source
- QgsProperty
- QgsRasterLayer
BAND: Band number
Parameter type: QgsProcessingParameterBand
Accepted data types:
- int
- QgsProperty
INTERVAL: Interval between contour lines
Parameter type: QgsProcessingParameterNumber
Accepted data types:
- int
- float
- QgsProperty
FIELD_NAME: Attribute name (if not set, no elevation attribute is attached)
Parameter type: QgsProcessingParameterString
Accepted data types:
- str
- QgsProperty
CREATE_3D: Produce 3D vector
Parameter type: QgsProcessingParameterBoolean
Accepted data types:
- bool
- int
- str
- QgsProperty
IGNORE_NODATA: Treat all raster values as valid
Parameter type: QgsProcessingParameterBoolean
Accepted data types:
- bool
- int
- str
- QgsProperty
NODATA: Input pixel value to treat as "nodata"
Parameter type: QgsProcessingParameterNumber
Accepted data types:
- int
- float
- QgsProperty
OFFSET: Offset from zero relative to which to interpret intervals
Parameter type: QgsProcessingParameterNumber
Accepted data types:
- int
- float
- QgsProperty
EXTRA: Additional command-line parameters
Parameter type: QgsProcessingParameterString
Accepted data types:
- str
- QgsProperty
OPTIONS: Additional creation options
Parameter type: QgsProcessingParameterString
Accepted data types:
- str
- QgsProperty
OUTPUT: Contours
Parameter type: QgsProcessingParameterVectorDestination
Accepted data types:
- str
- QgsProperty
- QgsProcessingOutputLayerDefinition
----------------
Outputs
----------------
OUTPUT: <QgsProcessingOutputVectorLayer>
Contours
Answered by Ben W on June 10, 2021
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