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https://github.com/nasa-gcn/pygcn
Python package for processing Gamma-ray Coordinates Network (GCN) notices
https://github.com/nasa-gcn/pygcn
astronomy python voevent
Last synced: about 2 hours ago
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Python package for processing Gamma-ray Coordinates Network (GCN) notices
- Host: GitHub
- URL: https://github.com/nasa-gcn/pygcn
- Owner: nasa-gcn
- License: gpl-3.0
- Created: 2013-02-09T16:25:14.000Z (almost 12 years ago)
- Default Branch: main
- Last Pushed: 2024-02-19T23:26:42.000Z (9 months ago)
- Last Synced: 2024-04-27T02:26:14.588Z (7 months ago)
- Topics: astronomy, python, voevent
- Language: Python
- Homepage: https://pypi.org/project/pygcn/
- Size: 2.6 MB
- Stars: 46
- Watchers: 12
- Forks: 23
- Open Issues: 4
-
Metadata Files:
- Readme: README.md
- Changelog: CHANGES.md
- License: LICENSE.md
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README
# PyGCN
[](https://codecov.io/gh/nasa-gcn/pygcn)
Anonymous VOEvent client for receiving GCN/TAN notices in XML format
The [Gamma-ray Coordinates Network/Transient Astronomy Network (GCN/TAN)][1] is
a system for distributing astronomical alerts, largely focused on operations of
and detections from high-energy satellite missions.
GCN/TAN disseminates both Notices (prompt, machine-readable alerts) and
Circulars (human-readable correspondence) through a handful of delivery methods
and formats.
This package implements a simple client that listens for [VOEvent][2] XML
format notices over the custom TCP/IP [VOEvent Transport Protocol][3]. By
default, it connects to one of the anonymous GCN/TAN server, so no sign-up
or configuration is necessary to begin receiving alerts.
## Installation
To install PyGCN, simply run:
$ pip install --user pygcn
## Usage
PyGCN provides an example script called `pygcn-listen` that will simply write
all VOEvents that it receives to files in the current directory. To try it out,
simply run:
$ pygcn-listen
and then type Control-C to quit.
## Writing a custom GCN handler
You can also write your own handler that performs a custom action for every GCN
that is received. A handler function takes two arguments: `payload`, the raw
content of the GCN, and `root`, the root element of the XML document as parsed
by [`lxml.etree`][5]. Here is a basic example:
```python
#!/usr/bin/env python
import gcn
# Define your custom handler here.
def handler(payload, root):
# Get the IVORN, or unique VOEvent ID, and print it.
print(root.attrib['ivorn'])
# Print all of the event attributes.
for param in root.findall('./What/Param'):
name = param.attrib['name']
value = param.attrib['value']
print('{} = {}'.format(name, value))
# Listen for VOEvents until killed with Control-C.
gcn.listen(handler=handler)
```
## Filtering
You can also filter events by notice type using
`gcn.include_notice_types` or `gcn.exclude_notice_types`.
Here is an example:
```python
#!/usr/bin/env python
import gcn
# Define your custom handler here.
@gcn.include_notice_types(
gcn.notice_types.FERMI_GBM_FLT_POS, # Fermi GBM localization (flight)
gcn.notice_types.FERMI_GBM_GND_POS, # Fermi GBM localization (ground)
gcn.notice_types.FERMI_GBM_FIN_POS) # Fermi GBM localization (final)
def handler(payload, root):
# Look up right ascension, declination, and error radius fields.
pos2d = root.find('.//{*}Position2D')
ra = float(pos2d.find('.//{*}C1').text)
dec = float(pos2d.find('.//{*}C2').text)
radius = float(pos2d.find('.//{*}Error2Radius').text)
# Print.
print('ra = {:g}, dec={:g}, radius={:g}'.format(ra, dec, radius))
# Listen for VOEvents until killed with Control-C.
gcn.listen(handler=handler)
```
[1]: http://gcn.gsfc.nasa.gov
[2]: http://www.ivoa.net/documents/VOEvent
[3]: http://www.ivoa.net/documents/Notes/VOEventTransport
[4]: https://docs.python.org/2/library/xml.etree.elementtree.html
[5]: http://lxml.de