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I'm trying to write a Python script to convert a vector layer using 4326 to EPSG:54002 World Equidistant Cylindrical for road distance calculations, but the script fails to do the conversion, I've tried numerous methods to get it right:

Using the re-project layer algorithm:

reprojectedLayer = processing.run("native:reprojectlayer", {'INPUT': roadLayer ,'TARGET_CRS': 'EPSG:54002', 'OUTPUT':'TEMPORARY_OUTPUT'})['OUTPUT']

reprojectedLayer = processing.run("native:reprojectlayer", {'INPUT': roadLayer ,'TARGET_CRS': QgsCoordinateReferenceSystem('EPSG:54002'), 'OUTPUT':'TEMPORARY_OUTPUT'})['OUTPUT']

Calling the setCrs method on the layer:

roadLayer.setCrs(QgsCoordinateReferenceSystem(54002, QgsCoordinateReferenceSystem.PostgisCrsId))

roadLayer.setCrs(QgsCoordinateReferenceSystem('EPSG:54002'))

Even just writing the layer to a file while specifying a different CRS:

QgsVectorFileWriter.writeAsVectorFormat(roadLayer, sys.argv[2] + "/roads", "utf-8",  QgsCoordinateReferenceSystem('EPSG:54002'), "GPKG")

Unfortunately, none of these have worked. If I save the file after any of the operations above and open it in QGIS it either just opens it fine as 4326 or opens it and displays a message that the CRS is invalid and that it will be defaulting to 4326.

One interesting thing to note is that when I specify the crs while writing the file, this pops up in the console:

proj_create_from_database: crs not found

It doesn't do that with the other methods, only when I write the file. This message doesn't make sense since if I try to reproject the layer to 54002 in QGIS, it works fine. Its only in the script that it fails.

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  • 54002 isn't a code in the EPSG registry
    – nmtoken
    Feb 12, 2020 at 6:59
  • Hmmm... Its listed in QGIS as a CRS and seems to work fine if I reproject to it using QGIS. the Python code I used to call the reproject layer method is from the processing log window. But I do see that epsg.io has it as ESRI:54002, let me try that.
    – Walter
    Feb 12, 2020 at 7:33
  • Okay no that didn't work, maybe the question I should be asking is, what CRS should I be using for measuring the length of a road (that isn't UTM)
    – Walter
    Feb 12, 2020 at 7:56
  • What if you put the proj definition in your code, rather than using an EPSG /ESRI number.. If that's possible.
    – nmtoken
    Feb 12, 2020 at 9:07
  • 1
    Unfortunately, there's no map projection that's great at road distances. If the data is in a limited area, some large scale (designed for a smallish area) projCRS would probably give okay values, but using a geodesic distance-based function would be better.
    – mkennedy
    Feb 12, 2020 at 18:18

1 Answer 1

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This script working fine for me :

params = {
    'INPUT': r'path/to/input/file.shp',
    'OUTPUT': r'path/to/the/export/file.shp',
    'TARGET_CRS': QgsCoordinateReferenceSystem('EPSG:54002')
}

processing.run("qgis:reprojectlayer", params)
vlayer = QgsVectorLayer(r'path/to/the/export/file.shp', 'reprojected', 'ogr')
QgsProject.instance().addMapLayer(vlayer)

The memory output work fine too :

params = {
    'INPUT': r'path/to/input/file.shp',
    'OUTPUT': 'memory:',
    'TARGET_CRS': QgsCoordinateReferenceSystem('EPSG:54002')
}

vlayer = processing.run("qgis:reprojectlayer", params)['OUTPUT']
QgsProject.instance().addMapLayer(vlayer)
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