Add function for HiPS to HEALPix conversion

hips/draw/healpix.py

@@ -1,17 +1,23 @@
 # Licensed under a 3-clause BSD style license - see LICENSE.rst
-from pathlib import Path
 import numpy as np
+from pathlib import Path
+from typing import Union, List
+from astropy.io import fits
 from astropy_healpix import healpy as hp
+import healpy as hp
+
 from ..tiles import HipsTile, HipsTileMeta, HipsSurveyProperties
 from ..utils.healpix import hips_tile_healpix_ipix_array
 
 __all__ = [
     'healpix_to_hips_tile',
     'healpix_to_hips',
+    'hips_to_healpix'
 ]
 
 
-def healpix_to_hips_tile(hpx_data, tile_width, tile_idx, file_format) -> HipsTile:
+def healpix_to_hips_tile(hpx_data: np.ndarray, tile_width: int,
+                         tile_idx: int, file_format: str) -> HipsTile:
     """Create single hips tile from healpix data given a tile index.
 
     Parameters
@@ -55,7 +61,8 @@ def healpix_to_hips_tile(hpx_data, tile_width, tile_idx, file_format) -> HipsTil
     return HipsTile.from_numpy(meta=meta, data=data)
 
 
-def healpix_to_hips(hpx_data, tile_width, base_path, file_format='fits'):
+def healpix_to_hips(hpx_data: np.ndarray, tile_width: int,
+                    base_path: Union[str, Path], file_format='fits') -> None:
     """Convert HEALPix image to HiPS.
 
     Parameters
@@ -88,3 +95,49 @@ def healpix_to_hips(hpx_data, tile_width, base_path, file_format='fits'):
 
     properties = HipsSurveyProperties(data=data)
     properties.write(base_path / 'properties')
+
+def hips_to_healpix(hips_url: str, hips_tiles: List[HipsTile], healpix_pixels: np.ndarray) -> np.ndarray:
+    """Given a HiPS survey, generate a HEALPix map.
+
+    Parameters
+    ----------
+    hips_tiles : List[HipsTile]
+        List of HiPS tiles.
+    hips_url : str
+        URL of HiPS survey.
+    healpix_pixels : `~numpy.ndarray`
+        HEALPix pixel numbers.
+
+    Returns
+    -------
+    healpix_map : `~numpy.ndarray`
+        HEALPix map.
+    """
+    # Query the HiPS survey properties.
+    hips_properties = HipsSurveyProperties.fetch(hips_url + "/properties")
+
+    hips_tile_width = hips_properties.tile_width
+    order = int(np.log2(hips_tile_width))
+
+    # xy_to_healpix = hips_tile_healpix_ipix_array(shift_order=order).flatten()
+
+    healpix_map = np.empty(hp.nside2npix(2 ** 12), dtype=np.double) # 2 ** 12?
+    healpix_map[:] = hp.pixelfunc.UNSEEN
+
+    for index, tile in enumerate(hips_tiles):
+        has_blank_value = False
+
+        if 'BLANK' in tile.data:
+            has_blank_value = True
+            blank_value_scaled = bscale * tile[0].header['BLANK'] + bzero
+
+        # healpix_index = xy_to_healpix[index]
+        pixel_value = tile.data
+
+        if has_blank_value and np.fabs(pixel_value - blank_value_scaled) < 1e-6:
+            pixel_value = hp.pixelfunc.UNSEEN
+
+        healpix_map_range = index * (hips_tile_width ** 2)
+        healpix_map[healpix_map_range: healpix_map_range + tile.meta.width] = pixel_value[0]
+
+    return healpix_map

hips/draw/tests/test_healpix.py

@@ -3,9 +3,11 @@
 import numpy as np
 from PIL import Image
 from astropy.io import fits
-from numpy.testing import assert_allclose
 from astropy_healpix import healpy as hp
-from ..healpix import healpix_to_hips
+from numpy.testing import assert_allclose
+
+from ..healpix import healpix_to_hips, healpix_to_hips_tile
+from ..healpix import hips_to_healpix
 
 
 @pytest.mark.parametrize('file_format', ['fits', 'png'])
@@ -36,3 +38,19 @@ def test_healpix_to_hips(tmpdir, file_format):
 
     properties = (tmpdir / 'properties').read_text(encoding=None)
     assert file_format in properties
+
+def test_hips_to_healpix(tmpdir):
+    nside, tile_width = 4, 2
+    npix = hp.nside2npix(nside)
+    healpix_data = np.arange(npix, dtype='uint8')
+
+    n_tiles = healpix_data.size // tile_width ** 2
+
+    tiles = []
+    for tile_idx in range(n_tiles):
+        tiles.append(healpix_to_hips_tile(hpx_data=healpix_data, tile_width=tile_width,
+                                          tile_idx=tile_idx, file_format='fits'))
+
+    healpix_map = hips_to_healpix(hips_url='http://alasky.u-strasbg.fr/Pan-STARRS/DR1/g',
+                                  hips_tiles=tiles,
+                                  healpix_pixels=healpix_data)