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DM-40746: Fix size and shape of HiPS Allsky file. #831

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merged 2 commits into from
Sep 14, 2023
Merged

DM-40746: Fix size and shape of HiPS Allsky file. #831

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266fd58
Change default Allsky tile size to 64 and add check for power-of-two.
erykoff Sep 13, 2023
5f27628
Fix size of Allsky file to be correctly rectangular.
erykoff Sep 13, 2023
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28 changes: 22 additions & 6 deletions python/lsst/pipe/tasks/hips.py
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Original file line number Diff line number Diff line change
Expand Up @@ -51,6 +51,8 @@
from lsst.afw.geom import makeHpxWcs
from lsst.resources import ResourcePath

from .healSparseMapping import _is_power_of_two


class HighResolutionHipsConnections(pipeBase.PipelineTaskConnections,
dimensions=("healpix9", "band"),
Expand Down Expand Up @@ -829,8 +831,9 @@ class GenerateHipsConfig(pipeBase.PipelineTaskConfig,
)
allsky_tilesize = pexConfig.Field(
dtype=int,
doc="Allsky.png tile size. Must be power of 2.",
default=512,
doc="Allsky tile size; must be power of 2. HiPS standard recommends 64x64 tiles.",
default=64,
check=_is_power_of_two,
)
png_gray_asinh_minimum = pexConfig.Field(
doc="AsinhMapping intensity to be mapped to black for grayscale png scaling.",
Expand Down Expand Up @@ -1532,7 +1535,20 @@ def _write_allsky_file(self, hips_base_path, allsky_order):
HEALPix order of the minimum order to make allsky file.
"""
tile_size = self.config.allsky_tilesize
n_tiles_per_side = int(np.sqrt(hpg.nside_to_npixel(hpg.order_to_nside(allsky_order))))

# The Allsky file format is described in
# https://www.ivoa.net/documents/HiPS/20170519/REC-HIPS-1.0-20170519.pdf
# From S4.3.2:
# The Allsky file is built as an array of tiles, stored side by side in
# the left-to-right order. The width of this array must be the square
# root of the number of the tiles of the order. For instance, the width
# of this array at order 3 is 27 ( (int)sqrt(768) ). To avoid having a
# too large Allsky file, the resolution of each tile may be reduced but
# must stay a power of two (typically 64x64 pixels rather than 512x512).

n_tiles = hpg.nside_to_npixel(hpg.order_to_nside(allsky_order))
n_tiles_wide = int(np.floor(np.sqrt(n_tiles)))
n_tiles_high = int(np.ceil(n_tiles / n_tiles_wide))

allsky_image = None

Expand All @@ -1549,15 +1565,15 @@ def _write_allsky_file(self, hips_base_path, allsky_order):
matches = re.match(pixel_regex, png_uri.basename())
pix_num = int(matches.group(1))
tile_image = Image.open(io.BytesIO(png_uri.read()))
row = math.floor(pix_num//n_tiles_per_side)
column = pix_num % n_tiles_per_side
row = math.floor(pix_num//n_tiles_wide)
column = pix_num % n_tiles_wide
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Row and column both use the width?

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Yeah, it's div and mod to get x/y from an ordered list.

box = (column*tile_size, row*tile_size, (column + 1)*tile_size, (row + 1)*tile_size)
tile_image_shrunk = tile_image.resize((tile_size, tile_size))

if allsky_image is None:
allsky_image = Image.new(
tile_image.mode,
(n_tiles_per_side*tile_size, n_tiles_per_side*tile_size),
(n_tiles_wide*tile_size, n_tiles_high*tile_size),
)
allsky_image.paste(tile_image_shrunk, box)

Expand Down