As of version
2.1.8, Gaia Sky uses Py4J instead of Jython as a mechanism to run Python scripts.
You can find lots of example scripts in the scripts folder of the project.
Gaia Sky scripts must be run with the system Python interpreter. They connect to a gateway service offered by a running instance of Gaia Sky. As of version
2.1.8, Gaia Sky is not responsible anymore to run the scripts.
In order to connect to the gateway server, you need a Python interpreter and the Py4J package. Find out how to install it here, or simply do, if you use
$ pip install py4j
Note that you may need to call this with elevated privileges.
You may also use your distribution or operating system package manager to install Py4J. Please, refer to your distribution or operating system documentation for more information. Find more information on the library at the Py4J homepage.
Running a test script
Then, launch Gaia Sky, download this script, open a terminal window (PowerShell in Windows) and run:
$ python asteroids-tour.py
The location from which you run the script does not matter. If all goes well, you should see no crashes anywhere, and Gaia Sky should be showing a nice tour of the asteroids in the DR2 catalog.
Have a look at the script. All lines which start with gs. are API calls which call methods in the Gaia Sky gateway server. What are API calls, you ask? See next section.
The scripting API
The scripting API is a set of methods which may be called from Python scripts to interact with Gaia Sky. The available methods differ depending on the version of Gaia Sky.
The only up-to-date API documentation for each version is in the interface header files themselves. Below is a list of links to the different APIs.
Writing scripts for Gaia Sky
In order to connect to Gaia Sky from Python, import
GatewayParameters, and then
create a gateway and get its entry point. The entry point is the object you can use to call
API methods on. The gateway must be closed at the end of the script for the Python program
to terminate correctly.
from py4j.java_gateway import JavaGateway, GatewayParameters gateway = JavaGateway(gateway_parameters=GatewayParameters(auto_convert=True)) gs = gateway.entry_point [...] gateway.close()
GatewayParameters(auto_convert=True) is not strictly necessary, but if you don’t use it you need
to convert Python lists to Java arrays yourself before calling the API.
Now, we can start calling API methods on
# Disable input gs.disableInput() gs.cameraStop() gs.minimizeInterfaceWindow() # Welcome gs.setHeadlineMessage("Welcome to the Gaia Sky") gs.setSubheadMessage("Explore Gaia, the Solar System and the whole Galaxy!") [...]
Find lots of example scripts here.
Logging to Gaia Sky and Python
When printing messages, you can either log to Gaia Sky or print to the standard output of the terminal where Python runs:
gs.print("This goes to the Gaia Sky log") print("This goes to the Python output")
In order to log messages to both outputs, you can define a function which takes a string and prints it out to both sides:
def pprint(text): gs.print(text) print(text) pprint("Hey, this is printed in both Gaia Sky AND Python!")
Method and attribute access
Py4J allows accessing public class methods but not public attrbiutes. In case you get objects from Gaia Sky, you can’t directly call public attributes, but need to access them via public methods:
# Get the Mars model object body = gs.getObject("Mars") # Get spherical coordinates radec = body.getPosSph() # DO NOT do this, it crashes! gs.print("RA/DEC: %f / %f" % (radec.x, radec.y)) # DO THIS instead gs.print("RA/DEC: %f / %f" % (radec.x(), radec.y()))
Strict parameter types
Please, be strict with the parameter types. Use floats when the method signature has floats and integers when it has integers. The scripting interface still tries to perform conversions under the hood but it is better to do it right from the beginning. For example, for the API method:
double galacticToInternalCartesian(double l, double b, double r);
may not work if called like this from Python:
gs.galacticToInternalCartesian(10, 43.5, 2)
Note that the first and third parameters are integers rather than floating-point numbers. Call it like this instead:
gs.galacticToInternalCartesian(10.0, 43.5, 2.0)
Loading datasets from scripts
Gaia Sky supports data loading from scripts using the STIL data provider.
It is really easy to load a
VOTable file from a script:
from py4j.java_gateway import JavaGateway, GatewayParameters gateway = JavaGateway(gateway_parameters=GatewayParameters(auto_convert=True)) gs = gateway.entry_point # Load dataset gs.loadDataset("dataset-name", "/path/to/dataset.vot") # Async insertion, let's make sure the data is available gs.sleep(2) # Now we can play around with it gs.hideDataset("dataset-name") # Show it again gs.showDataset("dataset-name")
Find an example of data loading in a script here.
Synchronizing with the main loop
Sometimes, when updating animations or creating camera paths, it is necessary to
sync the execution of scripts with the thread which runs the main loop (main thread).
However, the scripting engine runs scripts in separate threads asynchronously,
making it a non-obvious task to achieve this synchronization.
In order to fix this, a new mechanism has been added in Gaia Sky
2.0.3. Now, runnables
can be parked so that they run at the end of the update-render processing of each loop
cycle. A runnable is a class which extends
java.lang.Runnable, and implements
a very simple
public void run() method.
Runnables can be posted, meaning that they are run only once at the end fo the current cycle, or parked, meaning that they run until they stop or they are unparked. Parked runnables must provide a name identifier in order to be later accessed and unparked.
Let’s see an example of how to implement a frame counter in Python using
from py4j.java_gateway import JavaGateway, GatewayParameters, CallbackServerParameters class FrameCounterRunnable(object): def __init__(self): self.n = 0 def run(self): self.n = self.n + 1 if self.n % 30 == 0: gs.print("Number of frames: %d" % self.n) class Java: implements = ["java.lang.Runnable"] gateway = JavaGateway(gateway_parameters=GatewayParameters(auto_convert=True), callback_server_parameters=CallbackServerParameters()) gs = gateway.entry_point # We park a runnable which counts the frames and prints the current number # of frames every 30 of them gs.parkRunnable("frame_counter", FrameCounterRunnable()) gs.sleep(15.0) # We unpark the frame counter gs.unparkRunnable("frame_counter") gateway.close()
In this example, we park a runnable which counts frames for 15 seconds. Note that here we need
to pass a
CallbackServerParameters instance to the
A more useful example can be found here. In this one, a polyline is created between the Earth and the Moon. Then, a parked runnable is used to update the line points with the new postions of the bodies. Finally, time is started so that the bodies start moving and the line positions are updated correctly and in synch with the main thread.
As we said, you can find more examples in the
folder in the
Running and debugging scripts
In order to run scripts, you need a Python interpreter with the
python-py4j module installed in your system.
Load up Gaia Sky, open a new terminal window and run your script:
$ python script.py
Please, note that Gaia Sky needs to be running before the script is started for the connection to succeed.
To debug a script in the terminal using
pudb run this:
$ python -m pudb script.py