Generates a mappings.xml file for use with osgEarth CoverageLayer based on unique values in an attribute in a vector file.

generate_mappings.py

from osgeo import ogr
import click


def get_unique_values(layer, field):
    """
    Finds all the unique values in the vector layer
    """
    layer.ResetReading()

    values = set()
    for feature in layer:
        values.add(feature.GetField(field))
    return values

def generate_ids(values):
    """
    Given a list of unique values generate a map that maps the string value to
    an integer id
    """
    ids = {}
    id = 0
    for v in values:
        ids[v] = id
        id+=1
    return ids

def write_ids(layer, ids, input_field, output_field):
    layer.ResetReading()
    for feature in layer:
        value = feature.GetField(input_field)
        id = ids[value]
        feature.SetField(output_field, id)
        layer.SetFeature(feature)        

def write_mapping_file(ids, filename):
    with open(filename, 'w') as out:
        out.write("<mappings>\n")    
        for i in ids.items():
            out.write('  <mapping value="%s" biome_id="%s"/>\n' % (i[1], i[0]))
        out.write("</mappings>")

@click.command()
@click.argument('filename')
@click.option('--input_field', help='The field to generate unique ids for')
@click.option('--output_field', help='The field to write ids to')
def generate_mapping_ids(filename, input_field, output_field):    
    # Open the dataset for writing
    dataset = ogr.Open(filename, 1)
    if dataset is None:
        print("Couldn't open %s" % filename)    
        return 0

    layer = dataset.GetLayer(0)
    # Find all the unique values in the dataset
    values = get_unique_values(layer, input_field)    

    # Generate a map from values to ids
    ids = generate_ids(values)

    write_ids(layer, ids, input_field, output_field)

    write_mapping_file(ids, "mappings.xml")

    layer = None
    dataset = None
    
        
if __name__ == '__main__':
    generate_mapping_ids()