HpxNDMap¶

class gammapy.maps.HpxNDMap(geom, data=None, dtype='float32', meta=None, unit='')[source]¶

Bases: gammapy.maps.HpxMap

HEALPix map with any number of non-spatial dimensions.

This class uses a N+1D numpy array to represent the sequence of HEALPix image planes. Following the convention of WCS-based maps this class uses a column-wise ordering for the data array with the spatial dimension being tied to the last index of the array.

Parameters:	geom : `HpxGeom` HEALPIX geometry object. data : `ndarray` HEALPIX data array. If none then an empty array will be allocated. meta : `dict` Dictionary to store meta data. unit : str or `Unit` The map unit

Attributes Summary

`data`	Data array (`ndarray`)
`geom`	Map geometry (`Geom`)
`meta`	Map meta (`dict`)
`quantity`	Map data times unit (`Quantity`)
`unit`	Map unit (`Unit`)

Methods Summary

`coadd`(self, map_in[, weights])	Add the contents of `map_in` to this map.
`copy`(self, \\kwargs)	Copy map instance and overwrite given attributes, except for geometry.
`create`([nside, binsz, nest, map_type, …])	Factory method to create an empty HEALPix map.
`crop`(self, crop_width)	Crop the spatial dimensions of the map.
`downsample`(self, factor[, preserve_counts])	Downsample the spatial dimension by a given factor.
`fill_by_coord`(self, coords[, weights])	Fill pixels at `coords` with given `weights`.
`fill_by_idx`(self, idx[, weights])	Fill pixels at `idx` with given `weights`.
`fill_by_pix`(self, pix[, weights])	Fill pixels at `pix` with given `weights`.
`from_geom`(geom[, meta, data, map_type, …])	Generate an empty map from a `Geom` instance.
`from_hdu`(hdu[, hdu_bands])	Make a HpxNDMap object from a FITS HDU.
`from_hdulist`(hdu_list[, hdu, hdu_bands])	Make a HpxMap object from a FITS HDUList.
`get_by_coord`(self, coords)	Return map values at the given map coordinates.
`get_by_idx`(self, idx)	Return map values at the given pixel indices.
`get_by_pix`(self, pix)	Return map values at the given pixel coordinates.
`get_image_by_coord`(self, coords)	Return spatial map at the given axis coordinates.
`get_image_by_idx`(self, idx)	Return spatial map at the given axis pixel indices.
`get_image_by_pix`(self, pix)	Return spatial map at the given axis pixel coordinates
`interp_by_coord`(self, coords[, interp])	Interpolate map values at the given map coordinates.
`interp_by_pix`(self, pix[, interp])	Interpolate map values at the given pixel coordinates.
`iter_by_image`(self)	Iterate over image planes of the map.
`make_hdu`(self[, hdu, hdu_bands, sparse, conv])	Make a FITS HDU with input data.
`make_wcs_mapping`(self[, sum_bands, proj, …])	Make a HEALPix to WCS mapping object.
`pad`(self, pad_width[, mode, cval, order])	Pad the spatial dimensions of the map.
`plot`(self[, method, ax, normalize, proj, …])	Quickplot method.
`plot_interactive`(self[, rc_params])	Plot map with interactive widgets to explore the non spatial axes.
`read`(filename[, hdu, hdu_bands, map_type])	Read a map from a FITS file.
`reproject`(self, geom[, order, mode])	Reproject this map to a different geometry.
`set_by_coord`(self, coords, vals)	Set pixels at `coords` with given `vals`.
`set_by_idx`(self, idx, vals)	Set pixels at `idx` with given `vals`.
`set_by_pix`(self, pix, vals)	Set pixels at `pix` with given `vals`.
`slice_by_idx`(self, slices)	Slice sub map from map object.
`sum_over_axes`(self)	Sum over all non-spatial dimensions.
`to_hdulist`(self[, hdu, hdu_bands, sparse, conv])	Convert to `HDUList`.
`to_swapped`(self)	Return a new map with the opposite scheme (ring or nested).
`to_ud_graded`(self, nside[, preserve_counts])	Upgrade or downgrade the resolution of the map to the chosen nside.
`to_wcs`(self[, sum_bands, normalize, proj, …])	Make a WCS object and convert HEALPIX data into WCS projection.
`upsample`(self, factor[, preserve_counts])	Upsample the spatial dimension by a given factor.
`write`(self, filename[, overwrite])	Write to a FITS file.

Attributes Documentation

data¶: Data array (ndarray)

geom¶: Map geometry (Geom)

meta¶: Map meta (dict)

quantity¶: Map data times unit (Quantity)

unit¶: Map unit (Unit)

Methods Documentation

coadd(self, map_in, weights=None)¶

Add the contents of map_in to this map.

This method can be used to combine maps containing integral quantities (e.g. counts) or differential quantities if the maps have the same binning.

Parameters:	map_in : `Map` Input map. weights: `Map` or `~numpy.ndarray` The weight factors while adding

copy(self, **kwargs)¶

Copy map instance and overwrite given attributes, except for geometry.

Parameters:	**kwargs : dict Keyword arguments to overwrite in the map constructor.
Returns:	copy : `Map` Copied Map.

classmethod create(nside=None, binsz=None, nest=True, map_type='hpx', coordsys='CEL', data=None, skydir=None, width=None, dtype='float32', region=None, axes=None, meta=None, unit='')¶

Factory method to create an empty HEALPix map.

Parameters:

nside : int or ndarray: HEALPix NSIDE parameter. This parameter sets the size of the spatial pixels in the map.
binsz : float or ndarray: Approximate pixel size in degrees. An NSIDE will be chosen that correponds to a pixel size closest to this value. This option is superseded by nside.
nest : bool: True for HEALPix “NESTED” indexing scheme, False for “RING” scheme.
coordsys : {‘CEL’, ‘GAL’}, optional: Coordinate system, either Galactic (‘GAL’) or Equatorial (‘CEL’).
skydir : tuple or SkyCoord: 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.
map_type : {‘hpx’, ‘hpx-sparse’}: Map type. Selects the class that will be used to instantiate the map.
width : float: Diameter of the map in degrees. If None then an all-sky geometry will be created.
axes : list: List of MapAxis objects for each non-spatial dimension.
meta : dict: Dictionary to store meta data.
unit : str or Unit: The map unit

Returns:

map : HpxMap: A HPX map object.

crop(self, crop_width)[source]¶

Crop the spatial dimensions of the map.

Parameters:	crop_width : {sequence, array_like, int} Number of pixels cropped from the edges of each axis. Defined analogously to `pad_with` from `numpy.pad`.
Returns:	map : `Map` Cropped map.

downsample(self, factor, preserve_counts=True)[source]¶

Downsample the spatial dimension by a given factor.

Parameters:	factor : int Downsampling factor. preserve_counts : bool Preserve the integral over each bin. This should be true if the map is an integral quantity (e.g. counts) and false if the map is a differential quantity (e.g. intensity). axis : str Which axis to downsample. By default spatial axes are downsampled.
Returns:	map : `Map` Downsampled map.

fill_by_coord(self, coords, weights=None)¶

Fill pixels at coords with given weights.

Parameters:	coords : tuple or `MapCoord` Coordinate arrays for each dimension of the map. Tuple should be ordered as (lon, lat, x_0, …, x_n) where x_i are coordinates for non-spatial dimensions of the map. weights : `ndarray` Weights vector. Default is weight of one.

fill_by_idx(self, idx, weights=None)[source]¶

Fill pixels at idx with given weights.

Parameters:	idx : tuple Tuple of pixel index arrays for each dimension of the map. Tuple should be ordered as (I_lon, I_lat, I_0, …, I_n) for WCS maps and (I_hpx, I_0, …, I_n) for HEALPix maps. weights : `ndarray` Weights vector. Default is weight of one.

fill_by_pix(self, pix, weights=None)¶

Fill pixels at pix with given weights.

Parameters:	pix : tuple Tuple of pixel index arrays for each dimension of the map. Tuple should be ordered as (I_lon, I_lat, I_0, …, I_n) for WCS maps and (I_hpx, I_0, …, I_n) for HEALPix maps. Pixel indices can be either float or integer type. Float indices will be rounded to the nearest integer. weights : `ndarray` Weights vector. Default is weight of one.

static from_geom(geom, meta=None, data=None, map_type='auto', unit='', dtype='float32')¶

Generate an empty map from a Geom instance.

Parameters:

geom : Geom: Map geometry.
data : numpy.ndarray: data array
meta : dict: Dictionary to store meta data.
map_type : {‘wcs’, ‘wcs-sparse’, ‘hpx’, ‘hpx-sparse’, ‘auto’}: Map type. Selects the class that will be used to instantiate the map. The map type should be consistent with the geometry. If map_type is ‘auto’ then an appropriate map type will be inferred from type of geom.
unit : str or Unit: Data unit.

Returns:

map_out : Map: Map object

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

Make a HpxNDMap object from a FITS HDU.

Parameters:	hdu : `BinTableHDU` The FITS HDU hdu_bands : `BinTableHDU` The BANDS table HDU

classmethod from_hdulist(hdu_list, hdu=None, hdu_bands=None)¶

Make a HpxMap object from a FITS HDUList.

Parameters:	hdu_list : `HDUList` HDU list containing HDUs for map data and bands. hdu : str Name or index of the HDU with the map data. If None then the method will try to load map data from the first BinTableHDU in the file. hdu_bands : str Name or index of the HDU with the BANDS table.
Returns:	hpx_map : `HpxMap` Map object

get_by_coord(self, coords)¶

Return map values at the given map coordinates.

Parameters:	coords : tuple or `MapCoord` Coordinate arrays for each dimension of the map. Tuple should be ordered as (lon, lat, x_0, …, x_n) where x_i are coordinates for non-spatial dimensions of the map.
Returns:	vals : `ndarray` Values of pixels in the map. np.nan used to flag coords outside of map.

get_by_idx(self, idx)[source]¶

Return map values at the given pixel indices.

Parameters:	idx : tuple Tuple of pixel index arrays for each dimension of the map. Tuple should be ordered as (I_lon, I_lat, I_0, …, I_n) for WCS maps and (I_hpx, I_0, …, I_n) for HEALPix maps.
Returns:	vals : `ndarray` Array of pixel values. np.nan used to flag coordinate outside of map

get_by_pix(self, pix)¶

Return map values at the given pixel coordinates.

Parameters:	pix : tuple Tuple of pixel index arrays for each dimension of the map. Tuple should be ordered as (I_lon, I_lat, I_0, …, I_n) for WCS maps and (I_hpx, I_0, …, I_n) for HEALPix maps. Pixel indices can be either float or integer type.
Returns:	vals : `ndarray` Array of pixel values. np.nan used to flag coordinates outside of map

get_image_by_coord(self, coords)¶

Return spatial map at the given axis coordinates.

Parameters:	coords : tuple or dict Tuple should be ordered as (x_0, …, x_n) where x_i are coordinates for non-spatial dimensions of the map. Dict should specify the axis names of the non-spatial axes such as {‘axes0’: x_0, …, ‘axesn’: x_n}.
Returns:	map_out : `Map` Map with spatial dimensions only.

See also

get_image_by_coord, get_image_by_idx

interp_by_coord(self, coords, interp=1)[source]¶

Interpolate map values at the given map coordinates.

Parameters:

coords : tuple or MapCoord: Coordinate arrays for each dimension of the map. Tuple should be ordered as (lon, lat, x_0, …, x_n) where x_i are coordinates for non-spatial dimensions of the map.
interp : {None, ‘nearest’, ‘linear’, ‘cubic’, 0, 1, 2, 3}: Method to interpolate data values. By default no interpolation is performed and the return value will be the amplitude of the pixel encompassing the given coordinate. Integer values can be used in lieu of strings to choose the interpolation method of the given order (0=’nearest’, 1=’linear’, 2=’quadratic’, 3=’cubic’). Note that only ‘nearest’ and ‘linear’ methods are supported for all map types.
fill_value : None or float value: The value to use for points outside of the interpolation domain. If None, values outside the domain are extrapolated.

Returns:

vals : ndarray: Interpolated pixel values.

interp_by_pix(self, pix, interp=None)[source]¶: Interpolate map values at the given pixel coordinates.

iter_by_image(self)¶

Iterate over image planes of the map.

This is a generator yielding (data, idx) tuples, where data is a numpy.ndarray view of the image plane data, and idx is a tuple of int, the index of the image plane.

The image plane index is in data order, so that the data array can be indexed directly. See Iterating by image for further information.

make_hdu(self, hdu=None, hdu_bands=None, sparse=False, conv=None)¶

Make a FITS HDU with input data.

Parameters:	hdu : str The HDU extension name. hdu_bands : str The HDU extension name for BANDS table. sparse : bool Set INDXSCHM to SPARSE and sparsify the map by only writing pixels with non-zero amplitude. conv : {‘fgst-ccube’, ‘fgst-template’, ‘gadf’, None}, optional FITS format convention. If None this will be set to the default convention of the map.
Returns:	hdu_out : `BinTableHDU` or `ImageHDU` Output HDU containing map data.

make_wcs_mapping(self, sum_bands=False, proj='AIT', oversample=2, width_pix=None)[source]¶

Make a HEALPix to WCS mapping object.

Parameters:

sum_bands : bool: sum over non-spatial dimensions before reprojecting
proj : str: WCS-projection
oversample : float: Oversampling factor for WCS map. This will be the approximate ratio of the width of a HPX pixel to a WCS pixel. If this parameter is None then the width will be set from width_pix.
width_pix : int: 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.

Returns:

hpx2wcs : HpxToWcsMapping

pad(self, pad_width, mode='constant', cval=0, order=1)[source]¶

Pad the spatial dimensions of the map.

Parameters:

pad_width : {sequence, array_like, int}: Number of pixels padded to the edges of each axis.
mode : {‘edge’, ‘constant’, ‘interp’}: Padding mode. ‘edge’ pads with the closest edge value. ‘constant’ pads with a constant value. ‘interp’ pads with an extrapolated value.
cval : float: Padding value when mode=’consant’.
order : int: Order of interpolation when mode=’constant’ (0 = nearest-neighbor, 1 = linear, 2 = quadratic, 3 = cubic).

Returns:

map : Map: Padded map.

plot(self, method='raster', ax=None, normalize=False, proj='AIT', oversample=2, width_pix=1000, **kwargs)[source]¶

Quickplot method.

This will generate a visualization of the map by converting to a rasterized WCS image (method=’raster’) or drawing polygons for each pixel (method=’poly’).

Parameters:

method : {‘raster’,’poly’}: Method for mapping HEALPix pixels to a two-dimensional image. Can be set to ‘raster’ (rasterization to cartesian image plane) or ‘poly’ (explicit polygons for each pixel). WARNING: The ‘poly’ method is much slower than ‘raster’ and only suitable for maps with less than ~10k pixels.
proj : string, optional: Any valid WCS projection type.
oversample : float: Oversampling factor for WCS map. This will be the approximate ratio of the width of a HPX pixel to a WCS pixel. If this parameter is None then the width will be set from width_pix.
width_pix : int: 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.
**kwargs : dict: Keyword arguments passed to imshow.

Returns:

fig : Figure: Figure object.
ax : WCSAxes: WCS axis object
im : AxesImage or PatchCollection: Image object.

plot_interactive(self, rc_params=None, **kwargs)¶

Plot map with interactive widgets to explore the non spatial axes.

Parameters:	rc_params : dict Passed to `matplotlib.rc_context(rc=rc_params)` to style the plot. **kwargs : dict Keyword arguments passed to `WcsNDMap.plot`.

Examples

You can try this out e.g. using a Fermi-LAT diffuse model cube with an energy axis:

from gammapy.maps import Map

m = Map.read("$GAMMAPY_DATA/fermi_3fhl/gll_iem_v06_cutout.fits")
m.plot_interactive(add_cbar=True, stretch="sqrt")

If you would like to adjust the figure size you can use the rc_params argument:

rc_params = {'figure.figsize': (12, 6), 'font.size': 12}
m.plot_interactive(rc_params=rc_params)

static read(filename, hdu=None, hdu_bands=None, map_type='auto')¶

Read a map from a FITS file.

Parameters:

filename : str or Path: Name of the FITS file.
hdu : str: Name or index of the HDU with the map data.
hdu_bands : str: Name or index of the HDU with the BANDS table. If not defined this will be inferred from the FITS header of the map HDU.
map_type : {‘wcs’, ‘wcs-sparse’, ‘hpx’, ‘hpx-sparse’, ‘auto’}: Map type. Selects the class that will be used to instantiate the map. The map type should be consistent with the format of the input file. If map_type is ‘auto’ then an appropriate map type will be inferred from the input file.

Returns:

map_out : Map: Map object

reproject(self, geom, order=1, mode='interp')¶

Reproject this map to a different geometry.

Only spatial axes are reprojected, if you would like to reproject non-spatial axes consider using Map.interp_by_coord() instead.

Parameters:	geom : `Geom` Geometry of projection. mode : {‘interp’, ‘exact’} Method for reprojection. ‘interp’ method interpolates at pixel centers. ‘exact’ method integrates over intersection of pixels. order : int or str Order of interpolating polynomial (0 = nearest-neighbor, 1 = linear, 2 = quadratic, 3 = cubic).
Returns:	map : `Map` Reprojected map.

set_by_coord(self, coords, vals)¶

Set pixels at coords with given vals.

Parameters:	coords : tuple or `MapCoord` Coordinate arrays for each dimension of the map. Tuple should be ordered as (lon, lat, x_0, …, x_n) where x_i are coordinates for non-spatial dimensions of the map. vals : `ndarray` Values vector.

set_by_idx(self, idx, vals)[source]¶

Set pixels at idx with given vals.

Parameters:	idx : tuple Tuple of pixel index arrays for each dimension of the map. Tuple should be ordered as (I_lon, I_lat, I_0, …, I_n) for WCS maps and (I_hpx, I_0, …, I_n) for HEALPix maps. vals : `ndarray` Values vector.

set_by_pix(self, pix, vals)¶

Set pixels at pix with given vals.

Parameters:	pix : tuple Tuple of pixel index arrays for each dimension of the map. Tuple should be ordered as (I_lon, I_lat, I_0, …, I_n) for WCS maps and (I_hpx, I_0, …, I_n) for HEALPix maps. Pixel indices can be either float or integer type. Float indices will be rounded to the nearest integer. vals : `ndarray` Values vector.

slice_by_idx(self, slices)¶

Slice sub map from map object.

For usage examples, see Indexing and Slicing.

Parameters:	slices : dict Dict of axes names and integers or `slice` object pairs. Contains one element for each non-spatial dimension. For integer indexing the corresponding axes is dropped from the map. Axes not specified in the dict are kept unchanged.
Returns:	map_out : `Map` Sliced map object.

sum_over_axes(self)[source]¶

Sum over all non-spatial dimensions.

Returns:	map_out : `HpxNDMap` Summed map.

to_hdulist(self, hdu='SKYMAP', hdu_bands=None, sparse=False, conv='gadf')¶

Convert to HDUList.

Parameters:	hdu : str The HDU extension name. hdu_bands : str The HDU extension name for BANDS table. sparse : bool Set INDXSCHM to SPARSE and sparsify the map by only writing pixels with non-zero amplitude. conv : {‘fgst-ccube’,’fgst-template’,’gadf’,None}, optional FITS format convention. If None this will be set to the default convention of the map.
Returns:	hdu_list : `HDUList`

to_swapped(self)[source]¶

Return a new map with the opposite scheme (ring or nested).

Returns:	map : `HpxMap` Map object.

to_ud_graded(self, nside, preserve_counts=False)[source]¶

Upgrade or downgrade the resolution of the map to the chosen nside.

Parameters:	nside : int NSIDE parameter of the new map. preserve_counts : bool Choose whether to preserve counts (total amplitude) or intensity (amplitude per unit solid angle).
Returns:	map : `HpxMap` Map object.

to_wcs(self, sum_bands=False, normalize=True, proj='AIT', oversample=2, width_pix=None, hpx2wcs=None)[source]¶

Make a WCS object and convert HEALPIX data into WCS projection.

Parameters:

sum_bands : bool: Sum over non-spatial axes before reprojecting. If False then the WCS map will have the same dimensionality as the HEALPix one.
normalize : bool: Preserve integral by splitting HEALPIX values between bins?
proj : str: WCS-projection
oversample : float: Oversampling factor for WCS map. This will be the approximate ratio of the width of a HPX pixel to a WCS pixel. If this parameter is None then the width will be set from width_pix.
width_pix : int: 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.
hpx2wcs : HpxToWcsMapping: Set the HPX to WCS mapping object that will be used to generate the WCS map. If none then a new mapping will be generated based on proj and oversample arguments.

Returns:

map_out : WcsMap: WCS map object.

upsample(self, factor, preserve_counts=True)[source]¶

Upsample the spatial dimension by a given factor.

Parameters:	factor : int Upsampling factor. order : int Order of the interpolation used for upsampling. preserve_counts : bool Preserve the integral over each bin. This should be true if the map is an integral quantity (e.g. counts) and false if the map is a differential quantity (e.g. intensity). axis : str Which axis to upsample. By default spatial axes are upsampled.
Returns:	map : `Map` Upsampled map.

write(self, filename, overwrite=False, **kwargs)¶

Write to a FITS file.

Parameters:

filename : str: Output file name.
overwrite : bool: Overwrite existing file?
hdu : str: Set the name of the image extension. By default this will be set to SKYMAP (for BINTABLE HDU) or PRIMARY (for IMAGE HDU).
hdu_bands : str: Set the name of the bands table extension. By default this will be set to BANDS.
conv : str: FITS format convention. By default files will be written to the gamma-astro-data-formats (GADF) format. This option can be used to write files that are compliant with format conventions required by specific software (e.g. the Fermi Science Tools). Supported conventions are ‘gadf’, ‘fgst-ccube’, ‘fgst-ltcube’, ‘fgst-bexpcube’, ‘fgst-template’, ‘fgst-srcmap’, ‘fgst-srcmap-sparse’, ‘galprop’, and ‘galprop2’.
sparse : bool: Sparsify the map by dropping pixels with zero amplitude. This option is only compatible with the ‘gadf’ format.