This is the README for the CMB footprint module provided by LAMBDA.

The CMB footprint module is designed to show where different surveys are observing on the sky. All surveys for which we provide footprint regions are listed in the footprint.cfg file.

The code runs on both Python 2 (checken on 2.7.10) and Python 3 (checked on 3.4.3). The Python modules that are required for the code to run are

• Numpy
• Matplotlib
• Healpy
• Astropy
• Scipy

Numpy, Matplotlib, and Healpy are fairly obvious requirements. Astropy is needed so that human readable values can be input into the configuration file. Additionally, it can be used to read in WCS FITS files. Scipy is only used for the code that converts a WCS map to a Healpix map.

As long as your PYTHONPATH environment variable points to the directory where this module is located, the code should be able to run.

There are a couple examples on how to run the code shown in the examples/ subdirectory. Additionally, a Jupyter notebook is provided that shows the results from both of the example scripts. A background for the footprint is needed for the code to run. Backgrounds can be added to the configuration file, but will need to be downloaded the first time and the files can be large. Alternatively, any Healpix map can be input.

There are many different options when plotting the survey footprints. You can plot using any projection that Healpy provides and use most of the options that these projections provide. The coordinate system of the background map and the coordinate system of the plot should be provided though they do have default values ('G' and 'C' respectively). The coordinate system of each survey in the configuration file is assumed to be in Equatorial coordinates, though if an input map is provided instead of using the definitions in the configuration file, a coordinate system should be provided.

The input colors can be any string understood by matplotlib or an rgb triplet. The plotted regions for single survey will have the same color but a varying (0.5 to 1) alpha depending on the pixel value.

A copy of the latest configuration file is additionally stored on LAMBDA and an option can be set to download the latest version of the configuration file every time the code is run.

There are several different ways to input surveys to the configuration file. Here we will go over all the different types. For each types I will list the different keys that must go in the configuration file for that entry. The regions are specified as strings in the standard astropy coordinate format.

These are keys that are common to all the different types of configuration file entries.

• coord : 'C', 'E', or 'G' describing the coordinate system of the input map or the coordinate system of the input values.
• instrument : Instrument with which this data comes from. Multiple entries can have the same instrument.
• survey_type : Either 'background', 'cmb', 'cmbpol', or 'lss'. Used to separate entries into different tables when we generate a markdown file listing all the entries in the configuration file.
• citation : Citation describing how we got our survey footprint for the given experiment. Possible entries include a link to a file that we got our data form or and link to a paper from which we pulled values.

This reads in a footprint stored as a Healpix file. If the file does not exist in the path specified when you initialize the class, it will attempt to download the file from LAMBDA

• handler : hpx_file
• file : filename of the file
• checksum : The MD5 checksum of the file. It the checksum does not match the checksum of the local file, it will attempt to download it from LAMBDA.

This generates a disc footprint given a location and radius for the disc.

• handler : disc
• center : The center of the disc in lon,lat in human readable form (i.e. 4h12m,-12d4m). Values must be separated by a comma
• radius : The radius of the disc in human readable form

This generates a footprint given vertices of a polygon. There is no limit to the number of vertices, but the resulting polygon must be convex.

• handler : polygon
• vertex1, vertex2, ... : Lon,lat location of the vertex. The lon,lat values must be separated by a comma

This type generates a rectangle for the footprint. The rectangle is generated from a center point and a length of each side. The rectangle is always oriented along ra/dec lines. This will only look like a rectangle in a cartesian like projection where the x- and y-axes are ra/dec.

• handler : rectangle
• center : The center lon,lat of the rectangle.
• size : The length of the sides of the rectangle.

The last option is a combination option which combines the footprints of multiple other surveys listed in the configuration file. This is used so that a single survey can have multiple entries for different patches, so we can choose to plot a single patch or multiple patches without the code thinking they are different surveys. All component maps must have the same coordinate system because we just sum the Healpix maps together. Additionally, all combination maps are normalized to a maximum value of 1.

• handler : combination
• components : The names of the other entries in the configuration file that will be combined. Names must be separated by a comma.

Examples are shown in the examples directory. The Jupyter (.ipynb) notebook (https://github.com/nasa-lambda/cmb_footprint/blob/master/examples/plot_footprints.ipynb) can be visualized by github. The output is what I get on my computer.

The entries in the config file can be seen at https://github.com/nasa-lambda/cmb_footprint/blob/master/footprint_config.md or http://lambda.gsfc.nasa.gov/toolbox/footprint/configfile.cfm. These pages are automatically generated by gen_footprint_md.py based on the entries in the configuration file and is an easier way of seeing what surveys are predefined.

• Nathan Miller (nathan.j.miller@nasa.gov)