# Source code for dustmaps.unstructured_map

```
#!/usr/bin/env python
#
# unstructured_map.py
# Implements a class for querying dust maps with unstructured pixels. Sky
# coordinates are assigned to the nearest pixel.
#
# Copyright (C) 2016 Gregory M. Green
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License along
# with this program; if not, write to the Free Software Foundation, Inc.,
# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
#
from __future__ import print_function, division
import numpy as np
import astropy.coordinates as coordinates
import astropy.units as units
from scipy.spatial import cKDTree as KDTree
from .map_base import DustMap
[docs]class UnstructuredDustMap(DustMap):
"""
A class for querying dust maps with unstructured pixels. Sky coordinates are
assigned to the nearest pixel.
"""
[docs] def __init__(self, pix_coords, max_pix_scale, metric_p=2, frame=None):
"""
Args:
pix_coords (array-like :obj:`astropy.coordinates.SkyCoord`): The sky
coordinates of the pixels.
max_pix_scale (scalar :obj:`astropy.units.Quantity`): Maximum angular
extent of a pixel. If no pixel is within this distance of a
query point, NaN will be returned for that query point.
metric_p (Optional[:obj:`float`]): The metric to use. Defaults to 2, which
is the Euclidean metric. A value of 1 corresponds to the
Manhattan metric, while a value approaching infinity yields the
maximum component metric.
frame (Optional[:obj:`str`]): The coordinate frame to use internally. Must
be a frame understood by :obj:`astropy.coordinates.SkyCoord`.
Defaults to :obj:`None`, meaning that the frame will be inferred
from :obj:`pix_coords`.
"""
self._n_pix = pix_coords.shape[0]
self._metric_p = metric_p
if frame is None:
self._frame = pix_coords.frame
else:
self._frame = frame
# Tesselate the space
self._pix_vec = self._coords2vec(pix_coords)
self._kd = KDTree(self._pix_vec)
# Don't query more than this distance from any point
self._max_pix_scale = max_pix_scale.to('rad').value
def _coords2vec(self, coords):
"""
Converts from sky coordinates to unit vectors. Before conversion to unit
vectors, the coordiantes are transformed to the coordinate system used
internally by the :obj:`UnstructuredDustMap`, which can be set during
initialization of the class.
Args:
coords (:obj:`astropy.coordinates.SkyCoord`): Input coordinates to
convert to unit vectors.
Returns:
Cartesian unit vectors corresponding to the input coordinates, after
transforming to the coordinate system used internally by the
:obj:`UnstructuredDustMap`.
"""
# c = coords.transform_to(self._frame)
# vec = np.empty((c.shape[0], 2), dtype='f8')
# vec[:,0] = coordinates.Longitude(coords.l, wrap_angle=360.*units.deg).deg[:]
# vec[:,1] = coords.b.deg[:]
# return np.radians(vec)
c = coords.transform_to(self._frame).represent_as('cartesian')
vec_norm = np.sqrt(c.x**2 + c.y**2 + c.z**2)
vec = np.empty((c.shape[0], 3), dtype=c.x.dtype)
vec[:,0] = (c.x / vec_norm).value[:]
vec[:,1] = (c.y / vec_norm).value[:]
vec[:,2] = (c.z / vec_norm).value[:]
return vec
def _coords2idx(self, coords):
"""
Converts from sky coordinates to pixel indices.
Args:
coords (:obj:`astropy.coordinates.SkyCoord`): Sky coordinates.
Returns:
Pixel indices of the coordinates, with the same shape as the input
coordinates. Pixels which are outside the map are given an index
equal to the number of pixels in the map.
"""
x = self._coords2vec(coords)
idx = self._kd.query(x, p=self._metric_p,
distance_upper_bound=self._max_pix_scale)
return idx[1]
```