alpyca (2.0.4)

Python 3.7+ API library for all ASCOM Alpaca universal interfaces

Produced by the ASCOM Initiative, and derived from Ethan Chappel's Alpyca 1.0.0. Ethan kindly released the name Alpyca to the ASCOM Initiative, hence this expanded package starts life as Version 2.0.

Requirements

This package runs under Python 3.7 or later. It is compatible with most Linux distros, Windows , and MacOS. Dependencies are minimal: requests, netifaces, typing-extensions, python-dateutil, and enum-tools.

Installation

The package installs from PyPi as

pip install alpyca

or if you have the source code in a tar file, extract it and run (with Python 3)

python setup.py install

The dependencies listed above (and others they may depend on) are automatically installed with alpyca.

Current Status & Documentation

This version 2.0.4 is the third production release (2.0.3 is unpublished). The documentation is extensive and available online as Alpyca: API Library for Alpaca as well as a PDF Document here. See CHANGES.rst (on GitHub) for change log.

Feedback and Discussion

Feedback can be given on the ASCOM Driver and Application Development Support Forum. Please note that the protocols are universal and strictly curated. This library is an implementation of the protocols, not the protocols themselves. For background please visit About Alpaca and ASCOM, as well as the ASCOM Interface Principle, The Standards Process, and the General Requirements.

Example

First download, install and run the cross-platform Alpaca Omni Simulator which will give you fully functional simulators for all Alpaca devices, as well as a live OpenAPI/Swagger interface to the Alpaca RESTful endpoints (see the details below). This example will use the Telescope simulator. Assuming you are running the Omni Simulator on your local host at its default port of 32323, its address is then localhost:32323. Here is a sample program using alpaca:

    import time
    from alpaca.telescope import *      # Multiple Classes including Enumerations
    from alpaca.exceptions import *     # Or just the exceptions you want to catch

    T = Telescope('localhost:32323', 0) # Local Omni Simulator
    try:
        T.Connected = True
        print(f'Connected to {T.Name}')
        print(T.Description)
        T.Tracking = True               # Needed for slewing (see below)
        print('Starting slew...')
        T.SlewToCoordinatesAsync(T.SiderealTime + 2, 50)    # 2 hrs east of meridian
        while(T.Slewing):
            time.sleep(5)               # What do a few seconds matter?
        print('... slew completed successfully.')
        print(f'RA={T.RightAscension} DE={T.Declination}')
        print('Turning off tracking then attempting to slew...')
        T.Tracking = False
        T.SlewToCoordinatesAsync(T.SiderealTime + 2, 55)    # 5 deg slew N
        # This will fail for tracking being off
        print("... you won't get here!")
    except Exception as e:              # Should catch specific InvalidOperationException
        print(f'Slew failed: {str(e)}')
    finally:                            # Assure that you disconnect
        print("Disconnecting...")
        T.Connected = False

Results

    Connected to Alpaca Telescope Sim
    Software Telescope Simulator for ASCOM
    Starting slew...
    ... slew completed successfully.
    RA=10.939969572854931 DE=50
    Turning off tracking then attempting to slew...
    Slew failed: SlewToCoordinatesAsync is not allowed when tracking is False
    Disconnecting...
    done

Alpaca Omni Simulators

The ASCOM Alpaca Simulators are available via GitHub here. Using the [Latest] link, scroll down the Assets section and pick the package for your OS and CPU type. Extract all files to a directory and start via

./ascom-alpaca.simulators

(or the equivalent on Windows or MacOS). A web browser should appear. This is the primary user interface to the simulator server and simulated devices. Once you get this running you are ready to try the sample above.

ASCOM Remote

Any current ASCOM COM device that is hosted on a Windows system can have an Alpaca interface added via the ASCOM Remote Windows app. This app allows you to expose any of your Windows-hosted astronomy devices to the Alpaca world, making them reachable from programs using alpyca.

Wireshark

If you are interested in monitoring the HTTP/REST traffic that alpyca creates and exchanges with the Alpaca devices, you can install the Wireshark network protocol analyzer. One thing that trips people up is making the installation so that Wireshark has access to all of the network insterfaces without needing root privs (linux) or running "As Administrator" on Windows. Pay close attention the installation steps on this. On WIndows the capture driver installation will require elevation, as it is a privileged module. For example installinn on Linux (e.g Debian/Raspberry Pi) you'll see this, and be sure to answer Yes.

To watch Alpaca traffic, set this simple display filter http and tcp.port == 32323 (with 32323 being the port of the OmniSim, see above). You'll get a nice analysis of the Alpaca traffic like this