Transforming QgsPoint from one CRS to another using PyQGIS

Question

I would like to change the coordinates of QgsPoints imported from a csv file before saving it in shapefile.

I succeed to do all the step except the crs transformation, the output is keeping EPSG: 4326 instead of EPSG: 31370

#Set up inputs
absolute_path_to_csv_file = '/Users/X/Documents/.../Granulo.csv'
encoding = 'UTF-8'
delimiter = ';'
decimal = '.'
crs = 'epsg:4326'
x = 'X'
y = 'Y'
uri = f"file://{absolute_path_to_csv_file}?encoding={encoding}&delimiter={delimiter}&decimalPoint={decimal}&crs={crs}&xField={x}&yField={y}"
#Make a vector layer
layer = QgsVectorLayer(uri, "Points", "delimitedtext")
#Check if layer is valid
if not layer.isValid():
    print ("Layer not loaded")
#Add CSV data
QgsProject.instance().addMapLayer(layer)
#Transform CSV data
sourceCrs = QgsCoordinateReferenceSystem(4326)
destCrs = QgsCoordinateReferenceSystem(31370)
layer = QgsCoordinateTransform(sourceCrs, destCrs, QgsProject.instance())
myGeometryInstance.transform(layer)
#Write shapefile
QgsVectorFileWriter.writeAsVectorFormat(layer, '/Users/X/Documents/.../Points.shp', "UTF-8", layer.crs(), "ESRI Shapefile", layerOptions=['SHPT=POINT'])

The error message I obtain is the following:

Traceback (most recent call last):
  File "/Applications/QGIS-LTR.app/Contents/MacOS/../Resources/python/code.py", line 90, in runcode
    exec(code, self.locals)
  File "<input>", line 1, in <module>
  File "<string>", line 29, in <module>
NameError: name 'myGeometryInstance' is not defined

I am working on MacOs with QGIS 3.28.5-Firenze and Python 3.9.5

The code use is adapted from Adding points with coordinates delimited by commas from CSV file in QGIS Python Console & Transforming single QgsGeometry object from one CRS to another using PyQGIS

score 2 · Accepted Answer · answered Aug 11 '23 at 12:47

A slightly simpler solution

# ... previous code
#Make a vector layer
layer = QgsVectorLayer(uri, "Points", "delimitedtext")
#Check if layer is valid
if not layer.isValid():
    print ("Layer not loaded")
#Add CSV data
QgsProject.instance().addMapLayer(layer)
#prepare transform CSV data
sourceCrs = QgsCoordinateReferenceSystem(4326)
destCrs = QgsCoordinateReferenceSystem(31370)
tr = QgsCoordinateTransform(sourceCrs, destCrs, QgsProject.instance())
#Write shapefile
----> set the CRS of the writer to the destination CRS in the options
options = QgsVectorFileWriter.SaveVectorOptions()
options.ct = tr
options.fileEncoding = "utf-8"
options.driverName = "ESRI Shapefile"
result_code, *_ = QgsVectorFileWriter.writeAsVectorFormatV3(layer, '/Users/X/Documents/.../Points.shp', QgsProject.instance().transformContext(), options)

Thank you for your answer. It works nicely – C. Guff Aug 12 '23 at 07:03 — C. Guff, Aug 12 '23 at 07:03

score 0 · Answer 2 · edited Aug 11 '23 at 12:39

There a couple of issues with your current code.

myGeometryInstance is undeclared in your code - hence the NameError you get
You are overwriting your layer variable with a QgsCoordinateTransform object.
The transformation should be applied to a feature's geometry (alluded to by the variable name myGeometryInstance).

Try these adaptations:

# ... previous code
#Make a vector layer
layer = QgsVectorLayer(uri, "Points", "delimitedtext")
#Check if layer is valid
if not layer.isValid():
    print ("Layer not loaded")
#Add CSV data
QgsProject.instance().addMapLayer(layer)
#Transform CSV data
sourceCrs = QgsCoordinateReferenceSystem(4326)
destCrs = QgsCoordinateReferenceSystem(31370)
----> create the transform context (as a new variable)
tr = QgsCoordinateTransform(sourceCrs, destCrs, QgsProject.instance())
----> iterate through the features in the layer
for feat in layer.getFeatures():
    # ----> transform each feature in the layer (** be warned - this overwrites the feature's geometry **)
    myGeometryInstance = feat.geometry()
    myGeometryInstance.transform(tr)
#Write shapefile
----> set the CRS of the writer to the destination CRS
QgsVectorFileWriter.writeAsVectorFormat(layer, '/Users/X/Documents/.../Points.shp', "UTF-8", destCrs, "ESRI Shapefile", layerOptions=['SHPT=POINT'])

writeAsVectorFormat has been deprecated (which means it raises a warning to stop using it) for quite a while and should probably not be promoted as the function to use. — Kalak, Aug 11 '23 at 12:56

Transforming QgsPoint from one CRS to another using PyQGIS

2 Answers2

----> set the CRS of the writer to the destination CRS in the options

----> create the transform context (as a new variable)

----> iterate through the features in the layer

----> set the CRS of the writer to the destination CRS