31. Handling custom defined tags in QuakeML and the ObsPy Catalog/Event framework

QuakeML allows use of custom elements in addition to the ‘usual’ information defined by the QuakeML standard. It allows a) custom namespace attributes to QuakeML namespace tags and b) custom namespace subtags to QuakeML namespace elements. ObsPy can handle both basic custom tags in event type objects (a) and custom attributes (b) during input/output to/from QuakeML. The following basic example illustrates how to output a valid QuakeML file with custom xml tags/attributes:

from obspy import Catalog, UTCDateTime

extra = {'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'}}

cat = Catalog()
cat.extra = extra
cat.write('my_catalog.xml', format='QUAKEML',
          nsmap={'my_ns': 'http://test.org/xmlns/0.1'})

All custom information to be stored in the customized QuakeML 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. Catalog, Event, Pick). 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 QuakeML by providing a dictionary of namespace abbreviation mappings as nsmap parameter to Catalog.write(). The xml output of the above example looks like:

<?xml version='1.0' encoding='utf-8'?>
<q:quakeml xmlns:q='http://quakeml.org/xmlns/quakeml/1.2'
  <eventParameters publicID='smi:local/b425518c-9445-40c7-8284-d1f299ed2eac'
    <ns0:my_tag ns0:my_attrib1='123.4' ns0:my_attrib2='567'>true</ns0:my_tag>

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

from obspy import read_events

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

Custom tags can be nested:

from obspy import Catalog
from obspy.core 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

cat = Catalog()
cat.extra = AttribDict()
cat.extra.my_tag = my_tag
cat.write('my_catalog.xml', 'QUAKEML')

This will produce an xml output similar to the following:

<?xml version='1.0' encoding='utf-8'?>
<q:quakeml xmlns:q='http://quakeml.org/xmlns/quakeml/1.2'
  <eventParameters publicID='smi:local/97d2b338-0701-41a4-9b6b-5903048bc341'>

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

from obspy import read_events

cat = read_events('my_catalog.xml')

The order of extra tags can be controlled by using an OrderedDict for the extra attribute (using a plain dict or AttribDict can result in arbitrary order of tags):

from collections import OrderedDict
from obspy.core.event import Catalog, Event

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

my_tag1 = {'namespace': ns, 'value': 'some value 1'}
my_tag2 = {'namespace': ns, 'value': 'some value 2'}

event = Event()
cat = Catalog(events=[event])
event.extra = OrderedDict()
event.extra['myFirstExtraTag'] = my_tag2
event.extra['mySecondExtraTag'] = my_tag1
cat.write('my_catalog.xml', 'QUAKEML')