osmfile

Osmfile.py

Osmfile.py is a Python module that provides functionality for writing OpenStreetMap (OSM) XML format output files. It is used as part of the osm-fieldwork toolset, and can be used as part of a larger Python application. Currently it is only used by the CSVDump.py program.

When used, osmfile.py takes a Python data structure containing OSM data as input and generates an OSM XML format output file. The data structure consists of nested Python dictionaries and lists, with each dictionary representing an OSM node, way or relation, and each list representing a set of nodes, ways or relations.

For example, consider the following Python data structure representing a single OSM node:

node = {
    'id': 1234,
    'lat': 51.5074,
    'lon': -0.1278,
    'tags': {
        'name': 'Big Ben',
        'amenity': 'clock'
    }
}

To write this node to an OSM XML format output file using osmfile.py, you would first create a new osmfile.OsmWriter object, and then call the write() method, passing in the node dictionary as an argument:

from osmfile import OsmFile

writer = OsmFile('output.osm')
node_xml = writer.createNode(node)
way_xml = writer.createWay(way)
relation_xml = writer.createRelation(relation)
writer.add_tag('1234', 'amenity', 'post_office')
writer.write(node_xml)
writer.write(way_xml)
writer.write(relation_xml)
writer.close()

This would create XML code for the node, way, and relation using createNode(), createWay(), and createRelation() respectively. These methods return a string of XML code which is then written to the output file using writer.write(). The add_tag() method can be used to add additional tags to any of the elements being written to the file.

<node id="1234" lat="51.5074" lon="-0.1278">
<tag k="name" v="Big Ben"/>
<tag k="amenity" v="clock"/>
</node>

Osmfile.py also provides methods for writing OSM ways and relations to output files, and for adding tags to existing OSM nodes, ways and relations.

To write an OSM way to an output file, you would create a dictionary representing the way, with a nodes key containing a list of the node IDs that make up the way. For example:

way = {
    'id': 5678,
    'nodes': [1234, 5678, 9012],
    'tags': {
        'name': 'Oxford Street',
        'highway': 'primary'
    }
}

writer.write_way(way)

This would write the following XML code to the output file:

<way id="5678">
    <nd ref="1234"/>
    <nd ref="5678"/>
    <nd ref="9012"/>
    <tag k="name" v="Oxford Street"/>
    <tag k="highway" v="primary"/>
</way>

To write an OSM relation to an output file, you would create a dictionary representing the relation, with a members key containing a list of dictionaries representing the members of the relation. Each member dictionary should have type, ref and role keys, specifying the type of OSM object (node, way or relation), the ID of the object, and the role of the object in the relation. For example:

relation = {
    'id': 7890,
    'members': [
        {'type': 'way', 'ref': 5678, 'role': 'outer'},
        {'type': 'node', 'ref': 1234, 'role': 'admin_centre'}
    ],
    'tags': {
        'name': 'London Borough of Westminster',
        'type': 'boundary'
    }
}

writer.write_relation(relation)

This would write the following XML code to the output file:

<relation id="7890">
    <member type="way" ref="5678" role="outer"/>
    <member type="node" ref="1234" role="admin_centre"/>
    <tag k="name" v="London Borough of Westminster"/>
    <tag k="type" v="boundary"/>
</relation>

In addition to writing new OSM objects to an output file, osmfile.py also provides methods for adding tags to existing objects. To add a tag to an OSM object, you would call the add_tag() method, passing in the object's ID, the tag key and the tag value:

writer.add_tag('1234', 'amenity', 'post_office')

This would add the following XML code to the output file, as a child of the existing node element with ID 1234:

<tag k="amenity" v="post_office"/>

Note that the OsmWriter class also provides methods for closing the output file and flushing any buffered data to disk. You should call the close() method once you have finished writing all of your OSM data to the output file.