[FEATURE][processing] New algorithm "Contour Polygons"

With similar functionality to the existing GDAL contour algorithm, but exporting polygon representations of the contours

python/plugins/processing/algs/gdal/GdalAlgorithmProvider.py

@@ -37,7 +37,7 @@ from .buildvrt import buildvrt
 from .ClipRasterByExtent import ClipRasterByExtent
 from .ClipRasterByMask import ClipRasterByMask
 from .ColorRelief import ColorRelief
-from .contour import contour
+from .contour import contour, contour_polygon
 from .Datasources2Vrt import Datasources2Vrt
 from .fillnodata import fillnodata
 from .gdalinfo import gdalinfo
@@ -147,6 +147,7 @@ class GdalAlgorithmProvider(QgsProcessingProvider):
             ClipRasterByMask(),
             ColorRelief(),
             contour(),
+            contour_polygon(),
             Datasources2Vrt(),
             fillnodata(),
             gdalinfo(),

python/plugins/processing/algs/gdal/contour.py

@@ -139,7 +139,7 @@ class contour(GdalAlgorithm):
     def commandName(self):
         return 'gdal_contour'
 
-    def getConsoleCommands(self, parameters, context, feedback, executing=True):
+    def _buildArgsList(self, parameters, context, feedback, executing):
         inLayer = self.parameterAsRasterLayer(parameters, self.INPUT, context)
         if inLayer is None:
             raise QgsProcessingException(self.invalidRasterError(parameters, self.INPUT))
@@ -192,5 +192,61 @@ class contour(GdalAlgorithm):
 
         arguments.append(inLayer.source())
         arguments.append(output)
+        return arguments
+
+    def getConsoleCommands(self, parameters, context, feedback, executing=True):
+        arguments = self._buildArgsList(parameters, context, feedback, executing)
+        return [self.commandName(), GdalUtils.escapeAndJoin(arguments)]
+
+
+class contour_polygon(contour):
+
+    FIELD_NAME_MIN = 'FIELD_NAME_MIN'
+    FIELD_NAME_MAX = 'FIELD_NAME_MAX'
+
+    def __init__(self):
+        super().__init__()
+
+    def initAlgorithm(self, config=None):
+        super().initAlgorithm(config)
+        # FIELD_NAME isn't used in polygon mode
+        self.removeParameter(contour.FIELD_NAME)
+
+        self.addParameter(QgsProcessingParameterString(self.FIELD_NAME_MIN,
+                                                       self.tr('Attribute name for minimum elevation of contour polygon'),
+                                                       defaultValue='ELEV_MIN',
+                                                       optional=True))
+
+        self.addParameter(QgsProcessingParameterString(self.FIELD_NAME_MAX,
+                                                       self.tr('Attribute name for maximum elevation of contour polygon'),
+                                                       defaultValue='ELEV_MAX',
+                                                       optional=True))
+
+        # Need to replace the output parameter, as we are producing a different type of output
+        self.removeParameter(contour.OUTPUT)
+        self.addParameter(QgsProcessingParameterVectorDestination(
+            contour.OUTPUT, self.tr('Contours'), QgsProcessing.TypeVectorPolygon))
+
+    def name(self):
+        return 'contour_polygon'
+
+    def displayName(self):
+        return self.tr('Contour Polygons')
+
+    def getConsoleCommands(self, parameters, context, feedback, executing=True):
+        arguments = self._buildArgsList(parameters, context, feedback, executing)
+
+        fieldNameMin = self.parameterAsString(parameters, self.FIELD_NAME_MIN, context)
+        fieldNameMax = self.parameterAsString(parameters, self.FIELD_NAME_MAX, context)
+
+        if fieldNameMin:
+            arguments.insert(0, fieldNameMin)
+            arguments.insert(0, '-amin')
+
+        if fieldNameMax:
+            arguments.insert(0, fieldNameMax)
+            arguments.insert(0, '-amax')
+
+        arguments.insert(0, "-p")
 
         return [self.commandName(), GdalUtils.escapeAndJoin(arguments)]

python/plugins/processing/tests/GdalAlgorithmsRasterTest.py

@@ -47,7 +47,7 @@ from processing.algs.gdal.GridNearestNeighbor import GridNearestNeighbor
 from processing.algs.gdal.gdal2tiles import gdal2tiles
 from processing.algs.gdal.gdalcalc import gdalcalc
 from processing.algs.gdal.gdaltindex import gdaltindex
-from processing.algs.gdal.contour import contour
+from processing.algs.gdal.contour import contour, contour_polygon
 from processing.algs.gdal.gdalinfo import gdalinfo
 from processing.algs.gdal.hillshade import hillshade
 from processing.algs.gdal.aspect import aspect
@@ -404,6 +404,25 @@ class TestGdalRasterAlgorithms(unittest.TestCase, AlgorithmsTestBase.AlgorithmsT
                  source + ' ' +
                  outdir + '/check.jpg'])
 
+    def testContourPolygon(self):
+        context = QgsProcessingContext()
+        feedback = QgsProcessingFeedback()
+        source = os.path.join(testDataPath, 'dem.tif')
+        alg = contour_polygon()
+        alg.initAlgorithm()
+        with tempfile.TemporaryDirectory() as outdir:
+            self.assertEqual(
+                alg.getConsoleCommands({'INPUT': source,
+                                        'BAND': 1,
+                                        'FIELD_NAME_MIN': 'min',
+                                        'FIELD_NAME_MAX': 'max',
+                                        'INTERVAL': 5,
+                                        'OUTPUT': outdir + '/check.shp'}, context, feedback),
+                ['gdal_contour',
+                    '-p -amax max -amin min -b 1 -i 5.0 -f "ESRI Shapefile" ' +
+                    source + ' ' +
+                    outdir + '/check.shp'])
+
     def testContour(self):
         context = QgsProcessingContext()
         feedback = QgsProcessingFeedback()