32. Handling custom defined tags in StationXML with the Obspy Inventory

StationXML allows use of custom elements in addition to the ‘usual’ information defined by the StationXML standard. It allows a) custom namespace attributes to StationXML namespace tags and b) custom namespace subtags to StationXML namespace elements. ObsPy can handle both basic custom tags in all main elements (Network, Station, Channel, etc.) (a) and custom attributes (b) during input/output to/from StationXML. The following basic example illustrates how to output a StationXML file that contains additional xml tags/attributes:

from obspy import Inventory, UTCDateTime
from obspy.core.inventory import Network
from obspy.core.util import AttribDict

extra = AttribDict({
           'my_tag': {
                'value': True,
                'namespace': 'http://some-page.de/xmlns/1.0',
                'attrib': {
                  '{http://some-page.de/xmlns/1.0}my_attrib1': '123.4',
                  '{http://some-page.de/xmlns/1.0}my_attrib2': '567'
                }
            },
           'my_tag_2': {
                'value': u'True',
                'namespace': 'http://some-page.de/xmlns/1.0'
            },
           'my_tag_3': {
                'value': 1,
                'namespace': 'http://some-page.de/xmlns/1.0'
            },
           'my_tag_4': {
                'value': UTCDateTime('2013-01-02T13:12:14.600000Z'),
                'namespace': 'http://test.org/xmlns/0.1'
            },
           'my_attribute': {
                'value': 'my_attribute_value',
                'type': 'attribute',
                'namespace': 'http://test.org/xmlns/0.1'
            }
        })

inv = Inventory([Network('XX')], 'XX')
inv[0].extra = extra
inv.write('my_inventory.xml', format='STATIONXML',
          nsmap={'my_ns': 'http://test.org/xmlns/0.1',
                 'somepage_ns': 'http://some-page.de/xmlns/1.0'})

All custom information to be stored in the customized StationXML has to be stored in form of a dict or AttribDict object as the extra attribute of the object that should carry the additional custom information (e.g. Network, Station, Channel). The keys are used as the name of the xml tag, the content of the xml tag is defined in a simple dictionary: 'value' defines the content of the tag (the string representation of the object gets stored in the textual xml output). 'namespace' has to specify a custom namespace for the tag. 'type' can be used to specify whether the extra information should be stored as a subelement ('element', default) or as an attribute ('attribute'). Attributes to custom subelements can be provided in form of a dictionary as 'attrib'. If desired for better (human-)readability, namespace abbreviations in the output xml can be specified during output as StationXML by providing a dictionary of namespace abbreviation mappings as nsmap parameter to Inventory.write(). The xml output of the above example looks like:

<?xml version='1.0' encoding='UTF-8'?>
<FDSNStationXML xmlns:my_ns="http://test.org/xmlns/0.1" xmlns:somepage_ns="http://some-page.de/xmlns/1.0" xmlns="http://www.fdsn.org/xml/station/1" schemaVersion="1.0">
  <Source>XX</Source>
  <Module>ObsPy 1.0.2</Module>
  <ModuleURI>https://www.obspy.org</ModuleURI>
  <Created>2016-10-17T18:32:28.696287+00:00</Created>
  <Network code="XX">
    <somepage_ns:my_tag somepage_ns:my_attrib1="123.4" somepage_ns:my_attrib2="567">True</somepage_ns:my_tag>
    <my_ns:my_tag_4>2013-01-02T13:12:14.600000Z</my_ns:my_tag_4>
    <my_ns:my_attribute>my_attribute_value</my_ns:my_attribute>
    <somepage_ns:my_tag_2>True</somepage_ns:my_tag_2>
    <somepage_ns:my_tag_3>1</somepage_ns:my_tag_3>
  </Network>
</FDSNStationXML>

When reading the above xml again, using read_inventory(), the custom tags get parsed and attached to the respective Network type objects (in this example to the Inventory object) as .extra. Note that all values are read as text strings:

from obspy import read_inventory

inv = read_inventory('my_inventory.xml')
print(inv[0].extra)
AttribDict({
    u'my_tag': AttribDict({
        'attrib': {
          '{http://some-page.de/xmlns/1.0}my_attrib2': '567',
          '{http://some-page.de/xmlns/1.0}my_attrib1': '123.4'
        },
        'namespace': 'http://some-page.de/xmlns/1.0',
        'value': 'True'
    }),
    u'my_tag_4': AttribDict({
        'namespace': 'http://test.org/xmlns/0.1',
        'value': '2013-01-02T13:12:14.600000Z'
    }),
    u'my_attribute': AttribDict({
        'namespace': 'http://test.org/xmlns/0.1',
        'value': 'my_attribute_value'
    }),
    u'my_tag_2': AttribDict({
        'namespace': 'http://some-page.de/xmlns/1.0',
        'value': 'True'
    }),
    u'my_tag_3': AttribDict({
        'namespace': 'http://some-page.de/xmlns/1.0',
        'value': '1'
    })
})

Custom tags can be nested:

from obspy import Inventory
from obspy.core.inventory import Network
from obspy.core.util import AttribDict

ns = 'http://some-page.de/xmlns/1.0'

my_tag = AttribDict()
my_tag.namespace = ns
my_tag.value = AttribDict()

my_tag.value.my_nested_tag1 = AttribDict()
my_tag.value.my_nested_tag1.namespace = ns
my_tag.value.my_nested_tag1.value = 1.23E+10

my_tag.value.my_nested_tag2 = AttribDict()
my_tag.value.my_nested_tag2.namespace = ns
my_tag.value.my_nested_tag2.value = True

inv = Inventory([Network('XX')], 'XX')
inv[0].extra = AttribDict()
inv[0].extra.my_tag = my_tag
inv.write('my_inventory.xml', format='STATIONXML',
          nsmap={'somepage_ns': 'http://some-page.de/xmlns/1.0'})

This will produce an xml output similar to the following:

<?xml version='1.0' encoding='UTF-8'?>
<FDSNStationXML xmlns:somepage_ns="http://some-page.de/xmlns/1.0" xmlns="http://www.fdsn.org/xml/station/1" schemaVersion="1.0">
  <Source>XX</Source>
  <Module>ObsPy 1.0.2</Module>
  <ModuleURI>https://www.obspy.org</ModuleURI>
  <Created>2016-10-17T18:45:14.302265+00:00</Created>
  <Network code="XX">
    <somepage_ns:my_tag>
      <somepage_ns:my_nested_tag1>12300000000.0</somepage_ns:my_nested_tag1>
      <somepage_ns:my_nested_tag2>True</somepage_ns:my_nested_tag2>
    </somepage_ns:my_tag>
  </Network>
</FDSNStationXML>

The output xml can be read again using read_inventory() and the nested tags can be retrieved in the following way:

from obspy import read_inventory

inv = read_inventory('my_inventory.xml')
print(inv[0].extra.my_tag.value.my_nested_tag1.value)
print(inv[0].extra.my_tag.value.my_nested_tag2.value)
12300000000.0
True