fitsmap 0.2.0

Turn fits files/catalogs into a leafletjs map

FitsMap

FitsMap is a tool for displaying astronomical images and their associated catalogs, powered by LeafletJS.

Survey images can have dimensions in the tens of thousands of pixels in multiple bands. Examining images of this size can be difficult, especially in multiple bands. Memory constraints and highly specialized tools like DS9 can make simple high-level analysis infeasible or cumbersome. FitsMap addresses these two issues by converting large fits files and images into tiles that can be presented using LeafletJS. Another issue in examining survey images is examining a catalog of sources in the context of the images. FitsMap addresses this by converting a catalog of sources into JSON map markers, which can be viewed in the webpage. Additionally, these sources are searchable using the web interface by the column id.

Installation

Requirements:

• astropy

• imageio

• numpy

• matplotlib

• pillow

• scikit-image

• sharedmem

• tqdm

Use pip to install

pip install fitsmap

Usage

FitsMap is designed to address the following example. A user has multiple FITS files or PNG files that represent multiple bands of the same area of the sky, along with a catalog of sources within that area. For example, the directory might look like:

- path/to/data/
  - F125W.png
  - F160W.png
  - catalog.cat

To convert this diretory into a map is as simple as using fitsmap.convert.dir_to_map:

from fitsmap import convert

convert.dir_to_map.(
    "path/to/data",
    out_dir="/path/to/data/map",
    cat_wcs_fits_file="path/to/header_file.fits",
)

The first argument is which directory contains the files that we would like to convert into a map. In our case, this is path/to/dir. The next argument is the out_dir keyword argument that tells FitsMap where to put the generated webpage and supporting directories. In this example, the website will be built in a new subdirectory called map within path/to/data. Finally, the last argument is the cat_wcs_fits_file keyword argument. This tells FitsMap which header to use to parse any catalog files and convert them into map markers. In this example, one of the FITS files in the directory is used.

Once FitsMap is finished, the following will have been generated:

- path/to/data/map/
  - css/
  - F125W/
  - F160W/
  - js/
  - index.html

The directories F125W and F160W contain tiled versions of the input fits files. The css directory contains some supporting css files for clustering the markers. The js directory contains the json converted catalog sources. Finally, index.html is the webpage that contains the map. To use the map, simply open index.html with your favorite browser.

Parallelization (Linux/Mac Only)

FitsMap supports the parallelization(via Multiprocessing/sharedmem) of map creation in two ways:

• splitting images/catalogs into parallel tasks

• parallel tiling of an image

The settings for parallelization are set using the following keyword arguments:

• procs_per_task: Sets how many layers/catalogs to convert in parallel at a time.

• task_procs: How many tiles to generate in parallel

You can use both keyword arguments at the same time, but keep in mind the number of cpus available. For example, if procs_per_task=2 amd task_procs=2 then that will generate 6 new processes, 2 new processes for each task, and each of those will generate 2 new processes to tile an image in parallel.

Parallelization offers a significant speed up, so if there are cores available it makes sense to use them.

Notes

Notes on Image Conversion

FitsMap has two “image engines” that you can choose from for converting arrays into PNGS: PIL and Matplotlib.imshow. The default is to use PIL(pillow), which seems to be faster but expects all files to be already normalized and image ready. If the images are already normalized or are already PNGS, then this will work fine. Matplotlib, although a little slower, can accept FITS files without normalizing them. However, the default scaling is Linear and changing it isn’t currently supported. So images should have their dynamic range compressed before using FitsMap. Additionally, the default colomap passed to imshow is “gray”, but you can change this by changing the variable convert.MPL_CMAP to the string name of a Matplotlib colormap.

To ensure that pixels are rendered correctly and that map markers are placed correctly, any image that is not square is squared by padding the array with NaN values that are converted into transparent pixels in the PNG. As a consequence, if a FITS file contains NaNs when it is converted, those pixels will be converted into transparent pixels.

Notes on Catalog Conversion

Catalogs should be whitespace delimited text files with the first line containing the column names, and the following lines containing values. Catalogs need to have an id column with a unique value for each row. It also needs to have coordinates for each source, which can be one of the following pairs of columns (ra/dec) or (x/y).

All of the columns/values for each source will be stored in the description for object and will show up when the marker is clicked. As a consequence, having many columns will cause the following:

• Very large pop-up descriptions when a marker is clicked.

• Slower web page loading times due to the json marker file being larger.

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For more information see the docs or the code.