ztf_tiling

Note: unlikely to work for Dec>80deg since part of the tile will come close to wrapping over the pole.

Data:

data sources (in data/):

• ztf_fields.txt: list of ZTF field centers for primary and secondary grids. From XXX?
• ZTF_quadrantcenters.dat: centers of individual quadrants relative to the pointing center in the TAN projection OLD
• ZTF_quadrantcenters_20180813.dat: centers of individual quadrants, updated 2018-08-13 (by @dlakaplan)

Installation:

Standard python ./setup.py install

Requirements:

• astropy
• healpy (not actually for most functionality)

Usage:

Basic check to see if a position is within a tile:

from ztf_tiling import ztf_tiling
from astropy import units as u
from astropy.coordinates import SkyCoord

# test a position
c=SkyCoord(33.30833*u.deg, 32.73167*u.deg)
# get the tile that corresponds roughly to this position
Z=ztf_tiling.get_tile(651)
print(Z.inside(c))

should return 21. To figure out which CCD/quadrant:

print('CCD=%d' % ((Z.inside(c)-1)//4+1))
print('Quadrant=%d' % (Z.inside(c)-4*(Z.inside(c)-1)//4))

should return 6 and 1

Look at a all of the pixels in a healpix map and see what the probability for a tile is:

from ztf_tiling import ztf_tiling
import healpy as hp

nside=256
npix=hp.nside2npix(nside)

# coordinates for each pixel in the map
RA,Dec=hp.pix2ang(nside, np.arange(npix),lonlat=True)
Z=ztf_tiling.get_tile(651)
# this can be slow for a large value of npix
on=Z.inside(RA,Dec)
# now plot the result, rotating to the center of the tile:
hp.mollview(on,rot=(Z.RA.value,Z.Dec.value,0),xsize=4000)

Note that this will appear a bit blotchy toward the edges becase of the coarse pixelization.

Update quadrant centers (e.g., if the detector is re-shimmed)

There are two scripts in utils/. One will download a bunch of metadata using ZTFQuery for different tiles at different Decs (utils/get_tiledata.py) and write csv files with the results. The second (utils/write_quadrantoffsets.py) will write a new quadrants offset file that can be placed in data/. Note that this isn't done automatically, and the location of the quadrant offset file in ztf_tiling/ztf_tiling.py also needs to be changed.

Look at actual positions using ZTFQuery results

from ztfquery import query
zquery = query.ZTFQuery()

from ztf_tiling import ztf_tiling

zquery.load_metadata(sql_query='ccdid=1 and field=720 and qid=3 and filefracday=20180802305347')
# convert the results (should only be one in this case, else returns a list of WCS objects) to WCS
w=ztf_tiling.metadata2wcs(zquery.metatable)
# calculate footprint.  3072x3080 is the size of a quadrant in pixels
footprint=w.calc_footprint(axes=(3072,3080))

from astropy.coordinates import SkyCoord
from astropy import units as u

# pick a position (in this case the center):
c=SkyCoord(229.6432834462*u.deg,  37.23028328539*u.deg)

# check if it is on the quadrant.
# note that the second position needs to be an array/list also, so make it one
print(ztf_tiling.inside(footprint[:,0],footprint[:,1],[c.ra.value],[c.dec.value]))
# this should return True