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"""A slicer that uses a Healpix grid to calculate metric values (at the center of each healpixel).""" 

 

# Requires healpy 

# See more documentation on healpy here http://healpy.readthedocs.org/en/latest/tutorial.html 

# Also requires numpy (for histogram and power spectrum plotting) 

 

import numpy as np 

import healpy as hp 

from lsst.sims.maf.plots.spatialPlotters import HealpixSkyMap, HealpixHistogram, HealpixPowerSpectrum 

 

from .baseSpatialSlicer import BaseSpatialSlicer 

 

 

__all__ = ['HealpixSlicer'] 

 

 

class HealpixSlicer(BaseSpatialSlicer): 

""" 

A spatial slicer that evaluates pointings on a healpix-based grid. 

 

Note that a healpix slicer is intended to evaluate the sky on a spatial grid. 

Usually this grid will be something like RA as the lonCol and Dec as the latCol. 

However, it could also be altitude and azimuth, in which case altitude as latCol, 

and azimuth as lonCol. 

An additional alternative is to use HA/Dec, with lonCol=HA, latCol=Dec. 

 

When plotting with RA/Dec, the default HealpixSkyMap can be used, corresponding to 

{'rot': (0, 0, 0), 'flip': 'astro'}. 

When plotting with alt/az, either the LambertSkyMap can be used (if Basemap is installed) 

or the HealpixSkyMap can be used with a modified plotDict, 

{'rot': (90, 90, 90), 'flip': 'geo'}. 

When plotting with HA/Dec, only the HealpixSkyMap can be used, with a modified plotDict of 

{'rot': (0, -30, 0), 'flip': 'geo'}. 

 

Parameters 

---------- 

nside : int, optional 

The nside parameter of the healpix grid. Must be a power of 2. 

Default 128. 

lonCol : str, optional 

Name of the longitude (RA equivalent) column to use from the input data. 

Default fieldRA 

latCol : str, optional 

Name of the latitude (Dec equivalent) column to use from the input data. 

Default fieldDec 

latLonDeg : boolean, optional 

Flag indicating whether the lat and lon values in the input data are in 

degrees (True) or radians (False). 

Default True. 

verbose : boolean, optional 

Flag to indicate whether or not to write additional information to stdout during runtime. 

Default True. 

badval : float, optional 

Bad value flag, relevant for plotting. Default the hp.UNSEEN value (in order to properly flag 

bad data points for plotting with the healpix plotting routines). This should not be changed. 

useCache : boolean 

Flag allowing the user to indicate whether or not to cache (and reuse) metric results 

calculated with the same set of simulated data pointings. 

This can be safely set to True for slicers not using maps and will result in increased speed. 

When calculating metric results using maps, the metadata at each individual ra/dec point may 

influence the metric results and so useCache should be set to False. 

Default True. 

leafsize : int, optional 

Leafsize value for kdtree. Default 100. 

radius : float, optional 

Radius for matching in the kdtree. Equivalent to the radius of the FOV. Degrees. 

Default 1.75. 

useCamera : boolean, optional 

Flag to indicate whether to use the LSST camera footprint or not. 

Default False. 

rotSkyPosColName : str, optional 

Name of the rotSkyPos column in the input data. Only used if useCamera is True. 

Describes the orientation of the camera orientation compared to the sky. 

Default rotSkyPos. 

mjdColName : str, optional 

Name of the exposure time column. Only used if useCamera is True. 

Default observationStartMJD. 

chipNames : array-like, optional 

List of chips to accept, if useCamera is True. This lets users turn 'on' only a subset of chips. 

Default 'all' - this uses all chips in the camera. 

""" 

def __init__(self, nside=128, lonCol ='fieldRA', 

latCol='fieldDec', latLonDeg=True, verbose=True, badval=hp.UNSEEN, 

useCache=True, leafsize=100, radius=1.75, 

useCamera=False, rotSkyPosColName='rotSkyPos', 

mjdColName='observationStartMJD', chipNames='all'): 

"""Instantiate and set up healpix slicer object.""" 

super(HealpixSlicer, self).__init__(verbose=verbose, 

lonCol=lonCol, latCol=latCol, 

badval=badval, radius=radius, leafsize=leafsize, 

useCamera=useCamera, rotSkyPosColName=rotSkyPosColName, 

mjdColName=mjdColName, chipNames=chipNames, latLonDeg=latLonDeg) 

# Valid values of nside are powers of 2. 

# nside=64 gives about 1 deg resolution 

# nside=256 gives about 13' resolution (~1 CCD) 

# nside=1024 gives about 3' resolution 

# Check validity of nside: 

if not(hp.isnsideok(nside)): 

raise ValueError('Valid values of nside are powers of 2.') 

self.nside = int(nside) 

self.pixArea = hp.nside2pixarea(self.nside) 

self.nslice = hp.nside2npix(self.nside) 

self.spatialExtent = [0, self.nslice-1] 

self.shape = self.nslice 

if self.verbose: 

print('Healpix slicer using NSIDE=%d, ' % (self.nside) + \ 

'approximate resolution %f arcminutes' % (hp.nside2resol(self.nside, arcmin=True))) 

# Set variables so slicer can be re-constructed 

self.slicer_init = {'nside': nside, 'lonCol': lonCol, 'latCol': latCol, 

'radius': radius} 

if useCache: 

# useCache set the size of the cache for the memoize function in sliceMetric. 

binRes = hp.nside2resol(nside) # Pixel size in radians 

# Set the cache size to be ~2x the circumference 

self.cacheSize = int(np.round(4.*np.pi/binRes)) 

# Set up slicePoint metadata. 

self.slicePoints['nside'] = nside 

self.slicePoints['sid'] = np.arange(self.nslice) 

self.slicePoints['ra'], self.slicePoints['dec'] = self._pix2radec(self.slicePoints['sid']) 

# Set the default plotting functions. 

self.plotFuncs = [HealpixSkyMap, HealpixHistogram, HealpixPowerSpectrum] 

 

def __eq__(self, otherSlicer): 

"""Evaluate if two slicers are equivalent.""" 

# If the two slicers are both healpix slicers, check nsides value. 

result = False 

if isinstance(otherSlicer, HealpixSlicer): 

if otherSlicer.nside == self.nside: 

if (otherSlicer.lonCol == self.lonCol and otherSlicer.latCol == self.latCol): 

if otherSlicer.radius == self.radius: 

if otherSlicer.useCamera == self.useCamera: 

if otherSlicer.chipsToUse == self.chipsToUse: 

if otherSlicer.rotSkyPosColName == self.rotSkyPosColName: 

if np.all(otherSlicer.shape == self.shape): 

result = True 

return result 

 

def _pix2radec(self, islice): 

"""Given the pixel number / sliceID, return the RA/Dec of the pointing, in radians.""" 

# Calculate RA/Dec in RADIANS of pixel in this healpix slicer. 

# Note that ipix could be an array, 

# in which case RA/Dec values will be an array also. 

lat, ra = hp.pix2ang(self.nside, islice) 

# Move dec to +/- 90 degrees 

dec = np.pi/2.0 - lat 

return ra, dec