32. Connecting to a SeedLink Server¶
The obspy.seedlink module provides a Python implementation of the SeedLink client protocol. The obspy.seedlink.easyseedlink submodule contains a high-level interface to the SeedLink implementation that facilitates the creation of a SeedLink client.
32.1. The create_client function¶
The easiest way to connect to a SeedLink server is using the obspy.seedlink.easyseedlink.create_client() function to create a new instance of the EasySeedLinkClient class. It accepts as an argument a function that handles new data received from the SeedLink server, for example:
def handle_data(trace):
print('Received the following trace:')
print(trace)
print()
This function can then be passed to create_client() together with a SeedLink server URL to create a client instance:
client = create_client('geofon.gfz-potsdam.de', on_data=handle_data)
The client immediately connects to the server when it is created.
32.1.1. Sending INFO requests to the server¶
The client instance can be used to send SeedLink INFO requests to the server:
# Send the INFO:ID request
client.get_info('ID')
# Returns:
# <?xml version="1.0"?>\n<seedlink software="SeedLink v3.2 (2014.071)" organization="GEOFON" started="2014/09/01 14:08:37.4192"/>\n
The responses to INFO requests are in XML format. The client provides a shortcut to retrieve and parse the server’s capabilities (via an INFO:CAPABILITIES request):
>>> client.capabilities
['dialup', 'multistation', 'window-extraction', 'info:id', 'info:capabilities', 'info:stations', 'info:streams']
The capabilities are fetched and parsed when the attribute is first accessed and are cached after that.
32.1.2. Streaming data from the server¶
In order to start receiving waveform data, a stream needs to be selected. This is done by calling the select_stream() method:
client.select_stream('BW', 'MANZ', 'EHZ')
Multiple streams can be selected. SeedLink wildcards are also supported:
client.select_stream('BW', 'ROTZ', 'EH?')
After having selected the streams, the client is ready to enter streaming mode:
client.loop()
This starts streaming data from the server. Upon every complete trace that is received from the server, the function defined above is called with the trace object:
Received new data:
BW.MANZ..EHZ | 2014-09-04T19:47:25.625000Z - 2014-09-04T19:47:26.770000Z | 200.0 Hz, 230 samples
Received new data:
BW.ROTZ..EHZ | 2014-09-04T19:47:22.685000Z - 2014-09-04T19:47:24.740000Z | 200.0 Hz, 412 samples
Received new data:
BW.ROTZ..EHZ | 2014-09-04T19:47:24.745000Z - 2014-09-04T19:47:26.800000Z | 200.0 Hz, 412 samples
Received new data:
BW.ROTZ..EHN | 2014-09-04T19:47:20.870000Z - 2014-09-04T19:47:22.925000Z | 200.0 Hz, 412 samples
Received new data:
BW.ROTZ..EHN | 2014-09-04T19:47:22.930000Z - 2014-09-04T19:47:24.985000Z | 200.0 Hz, 412 samples
The create_client() function also accepts functions to be called when the connection terminates or when a SeedLink error is received. See the documentation for details.
32.2. Advanced usage: subclassing the client¶
For advanced use cases, subclassing the EasySeedLinkClient class allows for finer control over the instance. Implementing the same client as above:
class DemoClient(EasySeedLinkClient):
"""
A custom SeedLink client
"""
def on_data(self, trace):
"""
Override the on_data callback
"""
print('Received trace:')
print(trace)
print()
The documentation has more details about the client.