DECam Tiling for HSC - SSantosLab/desgw-map GitHub Wiki

We need to replace the tiling pattern for DECam, now that HSC is done.

Adopt the mathematics that DECals and BLISS adopted: http://www.mpe.mpg.de/~4most/4FS/geodesic_pattern_list.html

The reference for these geodesic patterns is here: Hardin, R. H., Sloane, N. J. A., & Smith, W. D. 2001, Tables of Spherical Codes with Icosahedral Symmetry (Florham Park: AT&T Shannon Lab.) For DECam I (David Schelgel) did a fairly thorough search of tiling patterns and offsets, and would be surprised if there were a solution with a mean density of 3 that had more uniform coverage. The attachment lists efficiencies from some of the other solutions in table form. For example, the g16752 pattern with appropriate offsets could boost the fraction of sky with 3 or more coverings from 74.4% to 78.4%, but at a cost of 5.5% more tiles (for an average covering of 3.16).

with code at: http://www.antiprism.com/index.html

specifically using the code at: http://www.antiprism.com/programs/geodesic.html

Setup

Follow the steps for your machine on www.antiprism.com.

In our case we used the source code and building instructions listed in the README:

Building
--------

These are instructions for building from a source tarball (see
README.git for building fron the Antiprism Git Repository). They
are not needed to run the Windows executables.

Antiprism uses the Autotools build system. The programs can be
built with

   ./configure
   make

and installed with

   sudo make install-strip

For DECam

We use the tiling pattern from the list of tiling patterns.

For DECam this is specifically:

geodesic_tiling_pattern_npts17282.txt

which was created using:

src/geodesic -c 2 -f 29 ico | src/off2crds | awk 'function acos2(a,h){return(atan2(((h)**2-(a)**2)**0.5,(a)))} BEGIN {pi=4.*atan2(1.,1.);} //{i++;x=$1;y=$2;z=$3;phi=atan2(y,x);theta=acos2(z,1.);ra=(phi*180./pi)+180.;dec=90.-(theta*180./pi);print ra,dec}' > geodesic_tiling_pattern_npts17282.txt

For HSC

For HSC we have to adopt a new tiling pattern. However the HSC tiling area is about 1.528, so we have to create a new tiling pattern using the mathematics above. We use the code corresponding to 18752 points on the sphere:

We create:

geodesic_tiling_pattern_npts18752.txt

using the code:

src/geodesic -c 2 -f 25 ico | src/off2crds | awk 'function acos2(a,h){return(atan2(((h)**2-(a)**2)**0.5,(a)))} BEGIN {pi=4.*atan2(1.,1.);} //{i++;x=$1;y=$2;z=$3;phi=atan2(y,x);theta=acos2(z,1.);ra=(phi*180./pi)+180.;dec=90.-(theta*180./pi);print ra,dec}' > geodesic_tiling_pattern_npts18752.txt

and then alter it by setting the -f 25 command to -f 30 to get an area per point consistent with HSC.

For HSC this is specifically:

geodesic_tiling_pattern_npts27002.txt

which was created using:

src/geodesic -c 2 -f 30 ico | src/off2crds | awk 'function acos2(a,h){return(atan2(((h)**2-(a)**2)**0.5,(a)))} BEGIN {pi=4.*atan2(1.,1.);} //{i++;x=$1;y=$2;z=$3;phi=atan2(y,x);theta=acos2(z,1.);ra=(phi*180./pi)+180.;dec=90.-(theta*180./pi);print ra,dec}' > geodesic_tiling_pattern_npts27002.txt