What 'options' are available in osgeo.gdal.ContourGenerateEx?

Question

I am working on generating contour polygons with gdal in python. I have a working script, which utilizes the osgeo.gdal.ContourGenerateEx function from the gdal library. However, I am having trouble finding documentation on this function. So far, I've been referencing the following:

• GDAL Python API (https://gdal.org/api/python/osgeo.gdal.html#osgeo.gdal.ContourGenerateEx)
• GDAL Autotest (https://github.com/OSGeo/gdal/blob/master/autotest/alg/contour.py)

On the GDAL Autotest script, lines 233 through 259 are:

def test_contour_3(input_tif, tmp_path):

    output_shp = str(tmp_path / "contour.shp")

    ogr_ds = ogr.GetDriverByName("ESRI Shapefile").CreateDataSource(output_shp)
    ogr_lyr = ogr_ds.CreateLayer("contour", geom_type=ogr.wkbMultiPolygon)
    field_defn = ogr.FieldDefn("ID", ogr.OFTInteger)
    ogr_lyr.CreateField(field_defn)
    field_defn = ogr.FieldDefn("elevMin", ogr.OFTReal)
    ogr_lyr.CreateField(field_defn)
    field_defn = ogr.FieldDefn("elevMax", ogr.OFTReal)
    ogr_lyr.CreateField(field_defn)

    ds = gdal.Open(input_tif)
    # gdal.ContourGenerateEx(ds.GetRasterBand(1), 0, 0, 0, [10, 20, 25], 0, 0, ogr_lyr, 0, 1, 1)
    gdal.ContourGenerateEx(
        ds.GetRasterBand(1),
        ogr_lyr,
        options=[
            "FIXED_LEVELS=10,20,25",
            "ID_FIELD=0",
            "ELEV_FIELD_MIN=1",
            "ELEV_FIELD_MAX=2",
            "POLYGONIZE=TRUE",
        ],
    )
    ds = None

Specifically, lines 248 through 257 show:

gdal.ContourGenerateEx(
    ds.GetRasterBand(1),
    ogr_lyr,
    options=[
        "FIXED_LEVELS=10,20,25",
        "ID_FIELD=0",
        "ELEV_FIELD_MIN=1",
        "ELEV_FIELD_MAX=2",
        "POLYGONIZE=TRUE",
    ],

I am interested in the "options" parameter of the gdal.ContourGenerateEx function. For instance, could I somehow specify a regular interval with an initial offset? In general, what options are available in this function? Is there a helper function to describe this?

Obviously the GDAL Autotest script describes options for fixed levels, ID field, elevation fields, and polygonize, but I am wondering what other options are available.

Here is my script for reference:

# import libraries
from osgeo import ogr
from osgeo import gdal 
from osgeo import osr 

# define input files
input_dem = "input path"

# define output files
output_gpkg = "output path"

# define output geopackage layer name
output_gpkg_layer = 'contour_polygons2'

# create raster data source
ds_dem = gdal.Open(input_dem)

# create spatial reference system
srs_26910 = osr.SpatialReference()

# define spatial reference system
srs_26910.ImportFromEPSG(26910)

# create geopackage driver
driver_gpkg = ogr.GetDriverByName('GPKG')

# create geopackage data source
ds_gpkg = driver_gpkg.CreateDataSource(output_gpkg)

# create geopackage layer
layer_contour1 = ds_gpkg.CreateLayer(output_gpkg_layer, geom_type=ogr.wkbMultiPolygon, srs=srs_26910)

# create field definitions
field_definition_elevMin = ogr.FieldDefn("elevMin", ogr.OFTReal)
field_definition_elevMax = ogr.FieldDefn("elevMax", ogr.OFTReal)

# create fields in layer
layer_contour1.CreateField(field_definition_elevMin)
layer_contour1.CreateField(field_definition_elevMax)

gdal.ContourGenerateEx(
    ds_dem.GetRasterBand(1),
    layer_contour1,
    options=[
        "FIXED_LEVELS=10,20,25",
        "ID_FIELD=-1",
        "ELEV_FIELD_MIN=0",
        "ELEV_FIELD_MAX=1",
        "POLYGONIZE=TRUE",
    ],
)

# close data sources and layers
layer_contour1 = None
ds_gpkg = None 
ds_dem = None

Answer 1

Detailed documentation of the GDALContourGenerateEx options can be found at least from the C API documentation https://gdal.org/api/gdal_alg.html#_CPPv421GDALContourGenerateEx15GDALRasterBandHPv12CSLConstList16GDALProgressFuncPv