diff --git a/python/lsst/pipe/tasks/hips.py b/python/lsst/pipe/tasks/hips.py index c0220d74d..9c0db34c1 100644 --- a/python/lsst/pipe/tasks/hips.py +++ b/python/lsst/pipe/tasks/hips.py @@ -1545,7 +1545,20 @@ def _write_allsky_file(self, hips_base_path, allsky_order): """ file_type = self.config.allsky_filetype 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 @@ -1562,15 +1575,15 @@ 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 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)