HpxGeom#

class gammapy.maps.HpxGeom[source]#

Bases: Geom

Geometry class for HEALPix maps.

This class performs mapping between partial-sky indices (pixel number within a HEALPix region) and all-sky indices (pixel number within an all-sky HEALPix map). Multi-band HEALPix geometries use a global indexing scheme that assigns a unique pixel number based on the all-sky index and band index. In the single-band case the global index is the same as the HEALPix index.

By default, the constructor will return an all-sky map. Partial-sky maps can be defined with the region argument.

Parameters:

nsidendarray: HEALPix NSIDE parameter, the total number of pixels is 12*nside*nside. For multi-dimensional maps one can pass either a single nside value or a vector of nside values defining the pixel size for each image plane. If nside is not a scalar then its dimensionality should match that of the non-spatial axes. If nest is True, nside must be a power of 2, less than 2**30.
nestbool, optional: Indexing scheme. If True, “NESTED” scheme. If False, “RING” scheme. Default is True.
frame{“icrs”, “galactic”}: Coordinate system. Default is “icrs”.
regionstr or tuple, optional: Spatial geometry for partial-sky maps. If None, the map will encompass the whole sky. String input will be parsed according to HPX_REG header keyword conventions. Tuple input can be used to define an explicit list of pixels encompassed by the geometry. Default is None.
axeslist: Axes for non-spatial dimensions.

Notes

For examples, see HEALPix-based maps

Attributes Summary

`axes`	List of non-spatial axes.
`axes_names`	All axes names.
`center_coord`	Map coordinates of the center of the geometry as a tuple.
`center_pix`	Pixel coordinates of the center of the geometry as a tuple.
`center_skydir`	Sky coordinate of the center of the geometry.
`data_shape`	Shape of the `ndarray` matching this geometry.
`data_shape_axes`	Shape of data of the non-spatial axes and unit spatial axes.
`frame`
`ipix`	HEALPix pixel and band indices for every pixel in the map.
`is_allsky`	Flag for all-sky maps.
`is_hpx`
`is_region`
`is_regular`	Flag identifying whether this geometry is regular in non-spatial dimensions.
`ndim`	Number of dimensions as an integer.
`nest`	Whether HEALPix order is nested as a boolean.
`npix`	Number of pixels in each band.
`npix_max`	Maximum number of pixels.
`nside`	NSIDE in each band.
`order`	The order in each band (`NSIDE = 2 ** ORDER`).
`ordering`	HEALPix ordering ('NESTED' or 'RING').
`pixel_scales`
`projection`	Map projection.
`region`	Region string.
`shape_axes`	Shape of non-spatial axes.
`width`	Width of the map.

Methods Summary

`contains`(coords)	Check if a given map coordinate is contained in the geometry.
`coord_to_pix`(coords)	Convert map coordinates to pixel coordinates.
`create`([nside, binsz, nest, frame, region, ...])	Create an HpxGeom object.
`crop`(crop_width)	Crop the geometry at the edges.
`cutout`(position, width, **kwargs)	Create a cutout around a given position.
`downsample`(factor[, axis_name])	Downsample the spatial dimension of the geometry by a given factor.
`from_hdu`(hdu[, hdu_bands])	Create an HPX object from a BinTable HDU.
`from_header`(header[, hdu_bands, format])	Create an HPX object from a FITS header.
`get_coord`([idx, flat, sparse, mode, axis_name])	Get the coordinate array for this geometry.
`get_idx`([idx, local, flat, sparse, mode, ...])	Get tuple of pixel indices for this geometry.
`get_index_list`(nside, nest, region)	Get list of pixels indices for all the pixels in a region.
`global_to_local`(idx_global[, ravel])	Compute global (all-sky) index from a local (partial-sky) index.
`interp_weights`(coords[, idxs])	Get interpolation weights for given coordinates.
`is_aligned`(other)	Check if HEALPix geoms and extra axes are aligned.
`is_allclose`(other[, rtol_axes, atol_axes])	Compare two data IRFs for equivalency.
`local_to_global`(idx_local)	Compute a global index (all-sky) from a local (partial-sky) index.
`pix_to_coord`(pix)	Convert pixel coordinates to map coordinates.
`pix_to_idx`(pix[, clip])	Convert pixel coordinates to pixel indices.
`region_mask`(regions)	Create a mask from a given list of regions.
`separation`(center)	Compute sky separation with respect to a given center.
`solid_angle`()	Solid angle array as a `Quantity` in `sr`.
`to_binsz`(binsz)	Change pixel size of the geometry.
`to_cube`(axes)	Append non-spatial axes to create a higher-dimensional geometry.
`to_header`([format])	Build and return FITS header for this HEALPix map.
`to_image`()	Create a 2D image geometry (drop non-spatial dimensions).
`to_nside`(nside)	Upgrade or downgrade the resolution to a given NSIDE.
`to_swapped`()	Geometry copy with swapped ORDERING (NEST->RING or vice versa).
`to_wcs_geom`([proj, oversample, width_pix])	Make a WCS projection appropriate for this HEALPix pixelization.
`to_wcs_tiles`([nside_tiles, margin])	Create WCS tiles geometries from HPX geometry with given nside.
`upsample`(factor)	Upsample the spatial dimension of the geometry by a given factor.

Attributes Documentation

axes#: List of non-spatial axes.

axes_names#: All axes names.

center_coord#: Map coordinates of the center of the geometry as a tuple.

center_pix#: Pixel coordinates of the center of the geometry as a tuple.

center_skydir#

Sky coordinate of the center of the geometry.

Returns:

centerSkyCoord: Center position.

data_shape#: Shape of the ndarray matching this geometry.

data_shape_axes#: Shape of data of the non-spatial axes and unit spatial axes.

frame#

ipix#: HEALPix pixel and band indices for every pixel in the map.

is_allsky#: Flag for all-sky maps.

is_hpx = True#

is_region = False#

is_regular#

Flag identifying whether this geometry is regular in non-spatial dimensions.

False for multi-resolution or irregular geometries. If True, all image planes have the same pixel geometry.

ndim#: Number of dimensions as an integer.

nest#: Whether HEALPix order is nested as a boolean.

npix#

Number of pixels in each band.

For partial-sky geometries this can be less than the number of pixels for the band NSIDE.

npix_max#: Maximum number of pixels.

nside#: NSIDE in each band.

order#

The order in each band (NSIDE = 2 ** ORDER).

Set to -1 for bands with NSIDE that is not a power of 2.

ordering#: HEALPix ordering (‘NESTED’ or ‘RING’).

pixel_scales#

projection#: Map projection.

region#: Region string.

shape_axes#: Shape of non-spatial axes.

width#: Width of the map.

Methods Documentation

contains(coords)[source]#

Check if a given map coordinate is contained in the geometry.

Parameters:

coordstuple or MapCoord: Tuple of map coordinates.

Returns:

containmentndarray: Bool array.

coord_to_pix(coords)[source]#

Convert map coordinates to pixel coordinates.

Parameters:

coordstuple: Coordinate values in each dimension of the map. This can either be a tuple of numpy arrays or a MapCoord object. If passed as a tuple then the ordering should be (longitude, latitude, c_0, …, c_N) where c_i is the coordinate vector for axis i.

Returns:

pixtuple: Tuple of pixel coordinates in image and band dimensions.

classmethod create(nside=None, binsz=None, nest=True, frame='icrs', region=None, axes=None, skydir=None, width=None)[source]#

Create an HpxGeom object.

Parameters:

nsideint or ndarray, optional: HEALPix NSIDE parameter. This parameter sets the size of the spatial pixels in the map. If nest is True, nside must be a power of 2, less than 2**30. Default is None.
binszfloat or ndarray, optional: Approximate pixel size in degrees. An nside will be chosen that corresponds to a pixel size closest to this value. This option is superseded by nside. Default is None.
nestbool, optional: Indexing scheme. If True, “NESTED” scheme. If False, “RING” scheme. Default is True.
frame{“icrs”, “galactic”}: Coordinate system, either Galactic (“galactic”) or Equatorial (“icrs”). Default is “icrs”.
regionstr, optional: HEALPix region string. Allows for partial-sky maps. Default is None.
axeslist, optional: List of axes for non-spatial dimensions. Default is None.
skydirtuple or SkyCoord, optional: Sky position of map center. Can be either a SkyCoord object or a tuple of longitude and latitude in deg in the coordinate system of the map. Default is None.
widthfloat, optional: Diameter of the map in degrees. If set the map will encompass all pixels within a circular region centered on skydir. Default is None.

Returns:

geomHpxGeom: A HEALPix geometry object.

Examples

>>> from gammapy.maps import HpxGeom, MapAxis
>>> axis = MapAxis.from_bounds(0,1,2)
>>> geom = HpxGeom.create(nside=16)
>>> geom = HpxGeom.create(binsz=0.1, width=10.0)
>>> geom = HpxGeom.create(nside=64, width=10.0, axes=[axis])
>>> geom = HpxGeom.create(nside=[32,64], width=10.0, axes=[axis])

crop(crop_width)[source]#

Crop the geometry at the edges.

Parameters:

crop_width{sequence, array_like, int}: Number of values cropped from the edges of each axis.

Returns:

geomGeom: Cropped geometry.

cutout(position, width, **kwargs)[source]#

Create a cutout around a given position.

Parameters:

positionSkyCoord: Center position of the cutout region.
widthAngle or Quantity: Diameter of the circular cutout region.

Returns:

cutoutWcsNDMap: Cutout map.

downsample(factor, axis_name=None)[source]#

Downsample the spatial dimension of the geometry by a given factor.

Parameters:

factorint: Downsampling factor.
axis_namestr: Axis to downsample.

Returns:

geomGeom: Downsampled geometry.

classmethod from_hdu(hdu, hdu_bands=None)[source]#

Create an HPX object from a BinTable HDU.

Parameters:

hduBinTableHDU: The FITS HDU.
hdu_bandsBinTableHDU, optional: The BANDS table HDU. Default is None.

Returns:

hpxHpxGeom: HEALPix geometry.

classmethod from_header(header, hdu_bands=None, format=None)[source]#

Create an HPX object from a FITS header.

Parameters:

headerHeader

The FITS header.

hdu_bandsBinTableHDU, optional

The BANDS table HDU. Default is None.

formatstr, optional

FITS convention. Default is None. If None the format is guessed. The following formats are supported:

“gadf”

“fgst-ccube”

“fgst-ltcube”

“fgst-bexpcube”

“fgst-srcmap”

“fgst-template”

“fgst-srcmap-sparse”

“galprop”

“galprop2”

“healpy”

Returns:

hpxHpxGeom: HEALPix geometry.

get_coord(idx=None, flat=False, sparse=False, mode='center', axis_name=None)[source]#

Get the coordinate array for this geometry.

Returns a coordinate array with the same shape as the data array. Pixels outside the geometry are set to NaN. Coordinates for a single image plane can be accessed by setting idx to the index tuple of a plane.

Parameters:

idxtuple, optional: A tuple of indices with one index for each non-spatial dimension. If defined only coordinates for the image plane with this index will be returned. If none then coordinates for all pixels will be returned. Default is None.
flatbool, optional: Return a flattened array containing only coordinates for pixels contained in the geometry. Default is False.

Returns:

coordstuple: Tuple of coordinate vectors with one vector for each dimension.

get_idx(idx=None, local=False, flat=False, sparse=False, mode='center', axis_name=None)[source]#

Get tuple of pixel indices for this geometry.

Returns all pixels in the geometry by default. Pixel indices for a single image plane can be accessed by setting idx to the index tuple of a plane.

Parameters:

idxtuple, optional: A tuple of indices with one index for each non-spatial dimension. If defined only pixels for the image plane with this index will be returned. If none then all pixels will be returned. Default is None.
localbool, optional: Flag to return local or global pixel indices. Local indices run from 0 to the number of pixels in a given image plane. Default is False.
flatbool, optional: Return a flattened array containing only indices for pixels contained in the geometry. Default is False.

Returns:

idxtuple: Tuple of pixel index vectors with one vector for each dimension.

static get_index_list(nside, nest, region)[source]#

Get list of pixels indices for all the pixels in a region.

Parameters:

nsideint: HEALPix NSIDE parameter.
nestbool: Indexing scheme. If True, “NESTED” scheme. If False, “RING” scheme.
regionstr: HEALPix region string.

Returns:

ilistndarray: List of pixel indices.

global_to_local(idx_global, ravel=False)[source]#

Compute global (all-sky) index from a local (partial-sky) index.

Parameters:

idx_globaltuple: A tuple of pixel indices with global HEALPix pixel indices.
ravelbool, optional: Return a raveled index. Default is False.

Returns:

idx_localtuple: A tuple of pixel indices with local HEALPix pixel indices.

interp_weights(coords, idxs=None)[source]#

Get interpolation weights for given coordinates.

Parameters:

coordsMapCoord or dict: Input coordinates.
idxsndarray, optional: Indices for non-spatial axes. Default is None.

Returns:

weightsndarray: Interpolation weights.

is_aligned(other)[source]#

Check if HEALPix geoms and extra axes are aligned.

Parameters:

otherHpxGeom: Other geometry.

Returns:

alignedbool: Whether geometries are aligned.

is_allclose(other, rtol_axes=1e-06, atol_axes=1e-06)[source]#

Compare two data IRFs for equivalency.

Parameters:

otherHpxGeom: Geometry to compare against.
rtol_axesfloat, optional: Relative tolerance for axes comparison. Default is 1e-6.
atol_axesfloat, optional: Relative tolerance for axes comparison. Default is 1e-6.

Returns:

is_allclosebool: Whether the geometry is all close.

local_to_global(idx_local)[source]#

Compute a global index (all-sky) from a local (partial-sky) index.

Parameters:

idx_localtuple: A tuple of pixel indices with local HEALPix pixel indices.

Returns:

idx_globaltuple: A tuple of pixel index vectors with global HEALPix pixel indices.

pix_to_coord(pix)[source]#

Convert pixel coordinates to map coordinates.

Parameters:

pixtuple: Tuple of pixel coordinates.

Returns:

coordstuple: Tuple of map coordinates.

pix_to_idx(pix, clip=False)[source]#

Convert pixel coordinates to pixel indices.

Returns -1 for pixel coordinates that lie outside the map.

Parameters:

pixtuple: Tuple of pixel coordinates.
clipbool: Choose whether to clip indices to the valid range of the geometry. If False then indices for coordinates outside the geometry range will be set -1. Default is False.

Returns:

idxtuple: Tuple of pixel indices.

region_mask(regions)[source]#

Create a mask from a given list of regions.

The mask is filled such that a pixel inside the region is filled with “True”. To invert the mask, e.g. to create a mask with exclusion regions the tilde (~) operator can be used (see example below).

Parameters:

regionsstr, Region or list of Region: Region or list of regions (pixel or sky regions accepted). A region can be defined as a string ind DS9 format as well. See http://ds9.si.edu/doc/ref/region.html for details.

Returns:

mask_mapWcsNDMap of boolean type: Boolean region mask.

separation(center)[source]#

Compute sky separation with respect to a given center.

Parameters:

centerSkyCoord: Center position.

Returns:

separationAngle: Separation angle array (1D).

solid_angle()[source]#

Solid angle array as a Quantity in sr.

The array has the same dimensionality as map.nside as all pixels have the same solid angle.

to_binsz(binsz)[source]#

Change pixel size of the geometry.

Parameters:

binszfloat or Quantity: New pixel size. A float is assumed to be in degree.

Returns:

geomWcsGeom: Geometry with new pixel size.

to_cube(axes)[source]#

Append non-spatial axes to create a higher-dimensional geometry.

This will result in a new geometry with N+M dimensions where N is the number of current dimensions and M is the number of axes in the list.

Parameters:

axeslist: Axes that will be appended to this geometry.

Returns:

geomGeom: Map geometry.

to_header(format='gadf', **kwargs)[source]#: Build and return FITS header for this HEALPix map.

to_image()[source]#

Create a 2D image geometry (drop non-spatial dimensions).

Returns:

geomGeom: Image geometry.

to_nside(nside)[source]#

Upgrade or downgrade the resolution to a given NSIDE.

Parameters:

nsideint: HEALPix NSIDE parameter.

Returns:

geomHpxGeom: A HEALPix geometry object.

to_swapped()[source]#

Geometry copy with swapped ORDERING (NEST->RING or vice versa).

Returns:

geomHpxGeom: A HEALPix geometry object.

to_wcs_geom(proj='AIT', oversample=2, width_pix=None)[source]#

Make a WCS projection appropriate for this HEALPix pixelization.

Parameters:

projstr, optional: Projection type of WCS geometry. Default is “AIT”.
oversamplefloat, optional: Oversampling factor for WCS map. This will be the approximate ratio of the width of a HEALPix pixel to a WCS pixel. If this parameter is None then the width will be set from width_pix. Default is 2.
width_pixint, optional: Width of the WCS geometry in pixels. The pixel size will be set to the number of pixels satisfying oversample or width_pix whichever is smaller. If this parameter is None then the width will be set from oversample. Default is None.

Returns:

wcsWcsGeom: WCS geometry.

to_wcs_tiles(nside_tiles=4, margin='0 deg')[source]#

Create WCS tiles geometries from HPX geometry with given nside.

The HEALPix geom is divide into superpixels defined by nside_tiles, which are then represented by a WCS geometry using a tangential projection. The number of WCS tiles is given by the number of pixels for the given nside_tiles.

Parameters:

nside_tilesint, optional: HEALPix NSIDE parameter for super pixel tiles. Default is 4.
marginQuantity, optional: Width margin of the WCS tile. Default is “0 deg”.

Returns:

wcs_tileslist: List of WCS tile geometries.

upsample(factor)[source]#

Upsample the spatial dimension of the geometry by a given factor.

Parameters:

factorint: Upsampling factor.
axis_namestr: Axis to upsample.

Returns:

geomGeom: Upsampled geometry.

__init__(nside, nest=True, frame='icrs', region=None, axes=None)[source]#

classmethod __new__(*args, **kwargs)#

HpxGeom#

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