🪡 Source Extractor Wrapper (SEW)

Overview

SEW provides a simple user interface for running Source Extractor from python.

Basic Usage

SEW seamlessly (😉) works with both numpy arrays and fits files, which is Source Extractor's required input format.

import sew

image = function_that_returns_image_as_numpy_array()

catalog = sew.run(image)

The Source Extractor catalog is returned as an astropy Table object.

If instead you have a fits file path, the function call looks identical:

catalog = sew.run(path_to_fits_file)

You can specify any Source Extractor configuration parameter as a keyword in the run function:

catalog = sew.run(path_to_fits_file, DETECT_THRESH=3, MAG_ZEROPOINT=27)

By default, a small number of measurement parameters are returned in the catalog:

    X_IMAGE
    Y_IMAGE
    FLUX_AUTO
    FLUX_RADIUS
    FWHM_IMAGE
    A_IMAGE
    B_IMAGE
    THETA_IMAGE
    ISOAREA_IMAGE
    FLAGS

To add additional measurement parameters, use the extra_params keyword:

catalog = sew.run(path_to_fits_file, extra_params=["ISO0", "ISO1", "ISO2"])

SEW also offers helper functions for doing common tasks. For example, to generate a sky model:

sky_model = sew.segmentation.create_sextractor_sky_model(path_to_fits_file)

The returned sky model is a numpy array. Similar to the run function, you can pass configuration parameters and/or extra measurement parameters as keywords.

Installation

🐍 Create an environment (Optional)

If you don't have one already, create a python environment for SEW. Here, we'll use conda to create a new development environment:

conda create -n sew-env python=3.8

Don't forget to activate the environment:

conda activate sew-env

🐑 🐑 Clone this repository

Using SSH:

git clone [email protected]:DragonflyTelescope/SEW.git

or

Using HTTPS:

git clone https://github.com/DragonflyTelescope/SEW.git

💿 Install SEW and its dependencies

Install the package using pip:

cd sew
python -m pip install .

This will install SEW and the dependencies listed in setup.py.

If you plan to develop the package, pip install in editable mode with the [dev] option:

python -m pip install -e '.[dev]'

In addition to the main package dependencies, this will install extra packages that are used for development (e.g., black and pytest).

🌌 Source Extractor

Now comes the fun part – installing Source Extractor!

Assuming you have Source Extractor installed, you must create an environment variable called SE_EXECUTABLE that points to the SExtractor executable.

For example, if you are running bash and the executable sextractor is in your path, you can append your .bashrc file like this:

echo 'export SE_EXECUTABLE="sextractor"' >> ~/.bashrc

Be sure to either open a new terminal or source your .bashrc file to save the environment variable.

🚀 Let's Go!

If all the above steps worked without any errors, you should be ready to SEW it up 🪡!