Getting Started

Dependencies

The following Python package dependencies should be installed on your system.

• numpy (required)

• healpy (optional, for handling healpix maps)

• astropy (optional, for updating internal IERS-A tables)

Installation

To use the latest version of QPoint, install via pip:

$ pip install qpoint

Otherwise, for developement work, clone the repository (https://github.com/arahlin/qpoint) and install manually:

$ pip install .

Or, if installing on a shared machine:

$ pip install --user .

Examples

Several example scripts are provided in the examples/ directory.

The script example_point.py shows some typical usage of the QPoint class, e.g. to construct timestreams in celestial coordinates from a set of local coordinates, and to compute offset detector pointing from a boresight location.

The script example_map.py shows some typical usage of the QMap class, e.g. to simulate detector timestreams with offset pointing from an input HEALpix sky realization, and to bin individual detector timestreams into a HEALpix map.

Algorithms

This document describes the quaternion-based algorithm used for computing equatorial right ascension and declination from the local coordinates of the (potentially moving) observing platform, including the various approximations that can be made to speed up the calculation. The document also covers computing detector pointing offset from the telescope boresight, using the same quaternion formalism.

Another document describes the mapmaking algorithm (implemented in the QMap class) for projecting time-ordered data onto a HEALPix spherical coordinate grid to make sky maps of Stokes parameters, typically used by telescopes designed for observing the cosmic microwave background (e.g. SPIDER).