UNIONSdata

A Python package for downloading multi-band imaging data from the Ultraviolet Near Infrared Optical Northern Survey (UNIONS). The package downloads the reduced images from the CANFAR VOSpace vault using the vos tool.

Features

✨ Multi-threaded downloads - Parallel downloading for improved performance
🎯 Flexible input methods - Use coordinates, tile numbers, or CSV catalogs
🌳 Spatial indexing - KD-tree for efficient coordinate-to-tile matching
📊 Progress tracking - Real-time download status and completion reports
⚙️ Configuration validation - Pydantic-based config with clear error messages
✂️ Cutout creation - Create and plot grayscale or RGB cutouts around objects of interest
🛡️ Graceful shutdown - Clean interrupt handling with temp file cleanup

Quick Start

# Install
pip install unionsdata

# Setup
unionsdata init    # Create your local copy of the config
unionsdata config  # Configure your download

# Download tiles
unionsdata download --tiles 217 292 --bands whigs-g cfis_lsb-r ps-i

Prerequisites

1. CANFAR VOSpace Account
   Register at https://www.canfar.net/en/

2. UNIONS survey membership
   Until the first public data release only collaboration members have access to the data.

3. Valid X.509 certificate for VOSpace access
   See below.

4. System dependencies
   Installed automatically (see pyproject.toml)

Installation & Setup

Option 1: Install from PyPI (Recommended)

Step 1: Install the package

pip install unionsdata

Step 2: Initialize the configuration file

unionsdata init

This creates your configuration file at:

• Linux/Mac: ~/.config/unionsdata/config.yaml
• Windows: %APPDATA%/unionsdata/config.yaml

Step 3: Edit the configuration

unionsdata config

This opens a terminal user interface (TUI). Set your paths, inputs and other parameters:

🔑 Important: Set up your CADC certificate in the TUI by clicking the Create/Renew button in the Paths tab and providing your CADC username and password. Credentials expire after 10 days. The button will indicate if a certificate is about to expire or already has. You can also manually create or renew your certificate in the terminal via:

cadc-get-cert -u YOUR_CANFAR_USERNAME

Option 2: Install from Source (For Development)

Step 1: Clone and install

# Clone the repository
git clone https://github.com/heesters-nick/unionsdata.git

# Change into the cloned repository
cd unionsdata

# Install in editable development mode
pip install -e ".[dev]"

Step 2: Edit the configuration file directly at src/unionsdata/config.yaml

Update the paths:

machine: local

paths_by_machine:
  local:
    root_dir_main: "/path/to/your/project"
    # **Important**: define location for downloaded data
    root_dir_data: "/path/to/download/data"
    dir_tables: "path/to/tables"
    dir_figures: "path/to/figures"
    cert_path: "/home/user/.ssl/cadcproxy.pem"

Step 3: Set up CANFAR credentials

cadc-get-cert -u YOUR_CANFAR_USERNAME

Usage

Command Line Interface

The package provides a unionsdata command with several subcommands:

Command	Description
unionsdata init	Initialize configuration file (first-time setup)
unionsdata config	Open terminal user interface to edit the config file
unionsdata download	Start downloading data
unionsdata	Shortcut alias for unionsdata download
unionsdata plot	Plot created cutouts

📝 Important - First Run: On your first download, the package automatically detects this and downloads tile availability information from CANFAR (~5 minutes one-time setup). A KD-tree spatial index is built for efficient coordinate-to-tile matching. Subsequent runs use the cached data.

To refresh tile availability data later, use the --update-tiles flag:

unionsdata download --update-tiles

Or tick the Update Tiles option in the TUI.

Download Specific Tiles

Download tiles by their tile numbers (x, y pairs):

unionsdata download --tiles 217 292 234 295

Download specific bands only:

unionsdata download --tiles 217 292 --bands whigs-g cfis_lsb-r ps-i

Download by Coordinates

Download tiles containing specific RA/Dec coordinates (in degrees):

unionsdata download --coordinates 227.3042 52.5285 231.4445 52.4447

Download from CSV Catalog

Download tiles for objects in a CSV file:

unionsdata download --table /path/to/catalog.csv

Your CSV should have columns for RA, Dec, and object ID. Example:

ID,ra,dec
M101,210.8022,54.3489
2,231.4445,52.4447

Note: Column names are customizable in the configuration file.

Download All Available Tiles

⚠️ Warning: This will download a large amount of data!

unionsdata download --all-tiles --bands whigs-g cfis_lsb-r

Using the Terminal User Interface (TUI)

Instead of using command-line arguments, you can configure downloads in the terminal user interface via

unionsdata config

A clickable user interface will open in your terminal where you can specify options for your download, cutout creation and subsequent cutout plotting. The configuration is grouped into several tabs: General, Paths, Inputs, Runtime, Bands, Tiles, Cutouts, and Plotting. The input fields are validated in real time: all drop down menus need to have a selection before allowing you to save the config file. Text boxes have a green border if the entry is valid and a red one if it is invalid. The info icons (𝑖) next to the settings in the TUI provide additional information. Choose either specific sky coordinates or a table of objects as an input and enable cutout creation if you want to plot your input objects after the data is downloaded. The application will augment your input table (or create a table from your input coordinates) and save it to the Tables directory. In the Plotting tab you can specify the catalog from which objects should be plotted under Catalog Name. The setting Auto automatically uses the most recent input. Once you have completed the configuration, hit the Save & Quit button.

Then run:

unionsdata download

Or simply:

unionsdata

If you have opted to create cutouts, you can plot them using:

unionsdata plot

Supported Bands

Band	Survey	Filter
cfis-u	CFIS	u-band
whigs-g	WHIGS	g-band
cfis-r	CFIS	r-band
cfis_lsb-r	CFIS	r-band (LSB optimized)
ps-i	Pan-STARRS	i-band
wishes-z	WISHES	z-band
ps-z	Pan-STARRS	z-band

Output Structure

Downloaded files are organized by tile and band:

data/
├── 217_292/
│   ├── whigs-g/
│   │   └── calexp-CFIS_217_292.fits
│   ├── cfis_lsb-r/
│   │   └── CFIS_LSB.217.292.r.fits
│   ├── ps-i/
│   │   └── PSS.DR4.217.292.i.fits
│   └── cutouts/
│       └── 217_292_cutouts_512.h5
└── 234_295/
    └── ...

Configuration Reference

Key Configuration Options

Section	Option	Description
Inputs	Input Source	Input method: Specific Tiles, Sky Coordinates, Table (CSV), or All Available Tiles
Runtime	Download Threads	Number of parallel download threads (1-32)
Runtime	Cutout Processes	Number of parallel cutout processes (1-32)
Bands	Band Selection	List of bands to download
Tiles	Update Tiles	Refresh tile lists from VOSpace
Tiles	Band Constraint	Minimum bands required per tile
Tiles	Require All Bands	Require that all requested bands are available to download a tile
Cutouts	Cutout Mode	Create cutouts around input coordinates: After Download or Direct Only. Works if input is Sky Coordinates or Table
Plotting	Catalog Name	Name of the catalog that should be used to plot cutouts around objects. Auto will use the most recent input
Plotting	RGB Bands	Select which bands should be mapped to red, green and blue to create color images. Locked in after selection. Hit the Reset button to start over.
Plotting	Display Mode	Grid: plot object cutouts in a grid; Channel: show individual bands + RGB image for every object

Band Configuration

Each band has a specific file structure and location. Example for the WHIGS g-band:

bands:
  whigs-g:
    name: "calexp-CFIS"
    band: "g"
    vos: "vos:cfis/whigs/stack_images_CFIS_scheme"
    suffix: ".fits"
    delimiter: "_"
    fits_ext: 1  # Data extension in fits file
    zfill: 0  # No zero padding the tile numbers in the file name
    zp: 27.0  # Zero point magnitude

Note: Data paths or file formats may change over time. Check the CANFAR vault for current locations:

Band	vault directory
cfis-u	tiles_DR6
whigs-g	whigs
cfis-r	tiles_DR6
cfis_lsb-r	tiles_LSB_DR6
ps-i	panstarrs
wishes-z	wishes_1
ps-z	panstarrs

Troubleshooting

Certificate Expired

cadc-get-cert -u YOUR_CANFAR_USERNAME

Config Issues

# Create a fresh copy of the default config file in your local environment
unionsdata init --force

Acknowledgments

• UNIONS collaboration
• CANFAR (Canadian Advanced Network for Astronomical Research)

Links

• UNIONS Survey
• CANFAR
• CANFAR Storage Documentation
• CANFAR VOSpace Documentation
• vostools

Support

For issues and questions:

• Open an issue on GitHub
• Contact: nick.heesters@epfl.ch

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