Map

class gammapy.maps.Map(geom, data, meta=None, unit='')

Bases: abc.ABC

Abstract map class.

This can represent WCS- or HEALPIX-based maps with 2 spatial dimensions and N non-spatial dimensions.

Parameters

geomGeom

Geometry

datandarray or Quantity

Data array

metadict

Dictionary to store meta data

unitstr or Unit

Data unit, ignored if data is a Quantity.

Attributes Summary

data	Data array (ndarray)
geom	Map geometry (Geom)
is_mask	Whether map is mask with bool dtype
meta	Map meta (dict)
quantity	Map data times unit (Quantity)
tag
unit	Map unit (Unit)

Methods Summary

apply_edisp(edisp)	Apply energy dispersion to map.
coadd(map_in[, weights])	Add the contents of map_in to this map.
copy(**kwargs)	Copy map instance and overwrite given attributes, except for geometry.
create(**kwargs)	Create an empty map object.
crop(crop_width)	Crop the spatial dimensions of the map.
cumsum(axis_name)	Compute cumulative sum along a given axis
downsample(factor[, preserve_counts, axis_name])	Downsample the spatial dimension by a given factor.
fill_by_coord(coords[, weights])	Fill pixels at coords with given weights.
fill_by_idx(idx[, weights])	Fill pixels at idx with given weights.
fill_by_pix(pix[, weights])	Fill pixels at pix with given weights.
fill_events(events)	Fill event coordinates (EventList).
from_geom(geom[, meta, data, unit, dtype])	Generate an empty map from a Geom instance.
from_hdulist(hdulist[, hdu, hdu_bands, …])	Create from astropy.io.fits.HDUList.
from_stack(maps[, axis, axis_name])	Create Map from list of images and a non-spatial axis.
get_by_coord(coords[, fill_value])	Return map values at the given map coordinates.
get_by_idx(idx)	Return map values at the given pixel indices.
get_by_pix(pix[, fill_value])	Return map values at the given pixel coordinates.
get_image_by_coord(coords)	Return spatial map at the given axis coordinates.
get_image_by_idx(idx)	Return spatial map at the given axis pixel indices.
get_image_by_pix(pix)	Return spatial map at the given axis pixel coordinates
get_spectrum([region, func, weights])	Extract spectrum in a given region.
integral(axis_name, coords, **kwargs)	Compute integral along a given axis
interp_by_coord(coords[, method, fill_value])	Interpolate map values at the given map coordinates.
interp_by_pix(pix[, method, fill_value])	Interpolate map values at the given pixel coordinates.
interp_to_geom(geom[, preserve_counts, …])	Interpolate map to input geometry.
iter_by_image()	Iterate over image planes of the map.
mask_nearest_position(position)	Given a sky coordinate return nearest valid position in the mask
normalize([axis_name])	Normalise data in place along a given axis.
pad(pad_width[, axis_name, mode, cval, method])	Pad the spatial dimensions of the map.
plot_grid([figsize, ncols])	Plot map as a grid of subplots for non-spatial axes
plot_interactive([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.
reduce(axis_name[, func, keepdims, weights])	Reduce map over a single non-spatial axis
reduce_over_axes([func, keepdims, …])	Reduce map over non-spatial axes
resample_axis(axis[, weights, ufunc])	Resample map to a new axis binning by grouping over smaller bins and apply ufunc to the bin contents.
set_by_coord(coords, vals)	Set pixels at coords with given vals.
set_by_idx(idx, vals)	Set pixels at idx with given vals.
set_by_pix(pix, vals)	Set pixels at pix with given vals.
slice_by_idx(slices)	Slice sub map from map object.
sum_over_axes([axes_names, keepdims, weights])	To sum map values over all non-spatial axes.
to_cube(axes)	Append non-spatial axes to create a higher-dimensional Map.
to_unit(unit)	Convert map to different unit
upsample(factor[, order, preserve_counts, axis])	Upsample the spatial dimension by a given factor.
write(filename[, overwrite])	Write to a FITS file.

Attributes Documentation

data

Data array (ndarray)

geom

Map geometry (Geom)

is_mask

Whether map is mask with bool dtype

meta

Map meta (dict)

quantity

Map data times unit (Quantity)

tag = 'map'

unit

Map unit (Unit)

Methods Documentation

apply_edisp(edisp)

Apply energy dispersion to map. Requires energy axis.

Parameters

edispgammapy.irf.EDispKernel

Energy dispersion matrix

Returns

mapWcsNDMap

Map with energy dispersion applied.

coadd(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_inMap

Input map.

weights: `Map` or `~numpy.ndarray`

The weight factors while adding

copy(**kwargs)

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

Parameters

**kwargsdict

Keyword arguments to overwrite in the map constructor.

Returns

copyMap

Copied Map.

static create(**kwargs)

Create an empty map object.

This method accepts generic options listed below, as well as options for HpxMap and WcsMap objects. For WCS-specific options, see WcsMap.create and for HPX-specific options, see HpxMap.create.

Parameters

framestr

Coordinate system, either Galactic (“galactic”) or Equatorial (“icrs”).

map_type{‘wcs’, ‘wcs-sparse’, ‘hpx’, ‘hpx-sparse’, ‘region’}

Map type. Selects the class that will be used to instantiate the map.

binszfloat or ndarray

Pixel size in degrees.

skydirSkyCoord

Coordinate of map center.

axeslist

List of MapAxis objects for each non-spatial dimension. If None then the map will be a 2D image.

dtypestr

Data type, default is ‘float32’

unitstr or Unit

Data unit.

metadict

Dictionary to store meta data.

regionSkyRegion

Sky region used for the region map.

Returns

mapMap

Empty map object.

abstract crop(crop_width)

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

mapMap

Cropped map.

cumsum(axis_name)

Compute cumulative sum along a given axis

Parameters

axis_namestr

Along which axis to integrate.

Returns

cumsumMap

Map with cumulative sum

abstract downsample(factor, preserve_counts=True, axis_name=None)

Downsample the spatial dimension by a given factor.

Parameters

factorint

Downsampling factor.

preserve_countsbool

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_namestr

Which axis to downsample. By default spatial axes are downsampled.

Returns

mapMap

Downsampled map.

fill_by_coord(coords, weights=None)

Fill pixels at coords with given weights.

Parameters

coordstuple 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.

weightsndarray

Weights vector. Default is weight of one.

abstract fill_by_idx(idx, weights=None)

Fill pixels at idx with given weights.

Parameters

idxtuple

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.

weightsndarray

Weights vector. Default is weight of one.

fill_by_pix(pix, weights=None)

Fill pixels at pix with given weights.

Parameters

pixtuple

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.

weightsndarray

Weights vector. Default is weight of one.

fill_events(events)

Fill event coordinates (EventList).

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

Generate an empty map from a Geom instance.

Parameters

geomGeom

Map geometry.

datanumpy.ndarray

data array

metadict

Dictionary to store meta data.

unitstr or Unit

Data unit.

Returns

map_outMap

Map object

static from_hdulist(hdulist, hdu=None, hdu_bands=None, map_type='auto', format=None, colname=None)

Create from astropy.io.fits.HDUList.

Parameters

hdulistHDUList

HDU list containing HDUs for map data and bands.

hdustr

Name or index of the HDU with the map data.

hdu_bandsstr

Name or index of the HDU with the BANDS table.

map_type{“auto”, “wcs”, “hpx”, “region”}

Map type.

format{‘gadf’, ‘fgst-ccube’, ‘fgst-template’}

FITS format convention.

colnamestr, optional

Data column name to be used for the HEALPix map.

Returns

map_outMap

Map object

classmethod from_stack(maps, axis=None, axis_name=None)

Create Map from list of images and a non-spatial axis.

The image geometries must be aligned, except for the axis that is stacked.

Parameters

mapslist of Map objects

List of maps

axisMapAxis

If a MapAxis is provided the maps are stacked along the last data axis and the new axis is introduced.

axis_namestr

If an axis name is as string the given the maps are stacked along the given axis name.

Returns

mapMap

Map with additional non-spatial axis.

get_by_coord(coords, fill_value=nan)

Return map values at the given map coordinates.

Parameters

coordstuple 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.

fill_valuefloat

Value which is returned if the position is outside of the projection footprint

Returns

valsndarray

Values of pixels in the map. np.nan used to flag coords outside of map.

abstract get_by_idx(idx)

Return map values at the given pixel indices.

Parameters

idxtuple

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

valsndarray

Array of pixel values. np.nan used to flag coordinate outside of map

get_by_pix(pix, fill_value=nan)

Return map values at the given pixel coordinates.

Parameters

pixtuple

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.

fill_valuefloat

Value which is returned if the position is outside of the projection footprint

Returns

valsndarray

Array of pixel values. np.nan used to flag coordinates outside of map

get_image_by_coord(coords)

Return spatial map at the given axis coordinates.

Parameters

coordstuple 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_outMap

Map with spatial dimensions only.

See also

get_image_by_idx, get_image_by_pix

Examples

import numpy as np
from gammapy.maps import Map, MapAxis
from astropy.coordinates import SkyCoord
from astropy import units as u

# Define map axes
energy_axis = MapAxis.from_edges(
    np.logspace(-1., 1., 4), unit='TeV', name='energy',
)

time_axis = MapAxis.from_edges(
    np.linspace(0., 10, 20), unit='h', name='time',
)

# Define map center
skydir = SkyCoord(0, 0, frame='galactic', unit='deg')

# Create map
m_wcs = Map.create(
    map_type='wcs',
    binsz=0.02,
    skydir=skydir,
    width=10.0,
    axes=[energy_axis, time_axis],
)

# Get image by coord tuple
image = m_wcs.get_image_by_coord(('500 GeV', '1 h'))

# Get image by coord dict with strings
image = m_wcs.get_image_by_coord({'energy': '500 GeV', 'time': '1 h'})

# Get image by coord dict with quantities
image = m_wcs.get_image_by_coord({'energy': 0.5 * u.TeV, 'time': 1 * u.h})

get_image_by_idx(idx)

Return spatial map at the given axis pixel indices.

Parameters

idxtuple

Tuple of scalar indices for each non spatial dimension of the map. Tuple should be ordered as (I_0, …, I_n).

Returns

map_outMap

Map with spatial dimensions only.

See also

get_image_by_coord, get_image_by_pix

get_image_by_pix(pix)

Return spatial map at the given axis pixel coordinates

Parameters

pixtuple

Tuple of scalar pixel coordinates for each non-spatial dimension of the map. Tuple should be ordered as (I_0, …, I_n). Pixel coordinates can be either float or integer type.

Returns

map_outMap

Map with spatial dimensions only.

See also

get_image_by_coord, get_image_by_idx

get_spectrum(region=None, func=<function nansum>, weights=None)

Extract spectrum in a given region.

The spectrum can be computed by summing (or, more generally, applying func) along the spatial axes in each energy bin. This occurs only inside the region, which by default is assumed to be the whole spatial extension of the map.

Parameters

region: `~regions.Region`

Region (pixel or sky regions accepted).

funcnumpy.func

Function to reduce the data. Default is np.nansum. For a boolean Map, use np.any or np.all.

weightsWcsNDMap

Array to be used as weights. The geometry must be equivalent.

Returns

spectrumRegionNDMap

Spectrum in the given region.

integral(axis_name, coords, **kwargs)

Compute integral along a given axis

This method uses interpolation of the cumulative sum.

Parameters

axis_namestr

Along which axis to integrate.

coordsdict or MapCoord

Map coordinates

**kwargsdict

Coordinates at which to evaluate the IRF

Returns

arrayQuantity

Returns 2D array with axes offset

abstract interp_by_coord(coords, method='nearest', fill_value=None)

Interpolate map values at the given map coordinates.

Parameters

coordstuple 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.

method{“nearest”, “linear”}

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.

fill_valueNone or float value

The value to use for points outside of the interpolation domain. If None, values outside the domain are extrapolated.

Returns

valsndarray

Interpolated pixel values.

abstract interp_by_pix(pix, method='nearest', fill_value=None)

Interpolate map values at the given pixel coordinates.

Parameters

pixtuple

Tuple of pixel coordinate arrays for each dimension of the map. Tuple should be ordered as (p_lon, p_lat, p_0, …, p_n) where p_i are pixel coordinates for non-spatial dimensions of the map.

method{“nearest”, “linear”}

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.

fill_valueNone or float value

The value to use for points outside of the interpolation domain. If None, values outside the domain are extrapolated.

Returns

valsndarray

Interpolated pixel values.

interp_to_geom(geom, preserve_counts=False, fill_value=0, **kwargs)

Interpolate map to input geometry.

Parameters

geomGeom

Target Map geometry

preserve_countsbool

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)

**kwargsdict

Keyword arguments passed to Map.interp_by_coord

Returns

interp_mapMap

Interpolated Map

iter_by_image()

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.

mask_nearest_position(position)

Given a sky coordinate return nearest valid position in the mask

If the mask contains additional axes, the mask is reduced over those.

Parameters

positionSkyCoord

Test position

Returns

positionSkyCoord

Nearest position in the mask

normalize(axis_name=None)

Normalise data in place along a given axis.

Parameters

axis_namestr

Along which axis to normalize.

pad(pad_width, axis_name=None, mode='constant', cval=0, method='linear')

Pad the spatial dimensions of the map.

Parameters

pad_width{sequence, array_like, int}

Number of pixels padded to the edges of each axis.

axis_namestr

Which axis to downsample. By default spatial axes are padded.

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.

cvalfloat

Padding value when mode=’consant’.

Returns

mapMap

Padded map.

plot_grid(figsize=None, ncols=3, **kwargs)

Plot map as a grid of subplots for non-spatial axes

Parameters

figsizetuple of int

Figsize to plot on

ncolsint

Number of columns to plot

**kwargsdict

Keyword arguments passed to Map.plot.

Returns

axesndarray of Axes

Axes grid

plot_interactive(rc_params=None, **kwargs)

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

Parameters

rc_paramsdict

Passed to matplotlib.rc_context(rc=rc_params) to style the plot.

**kwargsdict

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', format=None, colname=None)

Read a map from a FITS file.

Parameters

filenamestr or Path

Name of the FITS file.

hdustr

Name or index of the HDU with the map data.

hdu_bandsstr

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’, ‘region’}

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.

colnamestr, optional

data column name to be used of healix map.

Returns

map_outMap

Map object

reduce(axis_name, func=<ufunc 'add'>, keepdims=False, weights=None)

Reduce map over a single non-spatial axis

Parameters

axis_name: str

The name of the axis to reduce over

funcufunc

Function to use for reducing the data.

keepdimsbool, optional

If this is set to true, the axes which are summed over are left in the map with a single bin

weightsMap

Weights to be applied.

Returns

map_outMap

Map with the given non-spatial axes reduced

reduce_over_axes(func=<ufunc 'add'>, keepdims=False, axes_names=None, weights=None)

Reduce map over non-spatial axes

Parameters

funcufunc

Function to use for reducing the data.

keepdimsbool, optional

If this is set to true, the axes which are summed over are left in the map with a single bin

axes_names: list

Names of MapAxis to reduce over If None, all will reduced

weightsMap

Weights to be applied.

Returns

map_outMap

Map with non-spatial axes reduced

resample_axis(axis, weights=None, ufunc=<ufunc 'add'>)

Resample map to a new axis binning by grouping over smaller bins and apply ufunc to the bin contents.

By default, the map content are summed over the smaller bins. Other numpy ufunc can be used, e.g. np.logical_and, np.logical_or

Parameters

axisMapAxis

New map axis.

weightsMap

Array to be used as weights. The spatial geometry must be equivalent to other and additional axes must be broadcastable.

ufuncufunc

ufunc to use to resample the axis. Default is numpy.add.

Returns

mapMap

Map with resampled axis.

set_by_coord(coords, vals)

Set pixels at coords with given vals.

Parameters

coordstuple 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.

valsndarray

Values vector.

abstract set_by_idx(idx, vals)

Set pixels at idx with given vals.

Parameters

idxtuple

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.

valsndarray

Values vector.

set_by_pix(pix, vals)

Set pixels at pix with given vals.

Parameters

pixtuple

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.

valsndarray

Values vector.

slice_by_idx(slices)

Slice sub map from map object.

Parameters

slicesdict

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_outMap

Sliced map object.

sum_over_axes(axes_names=None, keepdims=True, weights=None)

To sum map values over all non-spatial axes.

Parameters

keepdimsbool, optional

If this is set to true, the axes which are summed over are left in the map with a single bin

axes_names: list of str

Names of MapAxis to reduce over. If None, all will summed over

weightsMap

Weights to be applied. The Map should have the same geometry.

Returns

map_outMap

Map with non-spatial axes summed over

to_cube(axes)

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

This will result in a Map with 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. The data is reshaped onto the new geometry

Parameters

axeslist

Axes that will be appended to this Map. The axes should have only one bin

Returns

mapWcsNDMap

new map

to_unit(unit)

Convert map to different unit

Parameters

unitUnit or str

New unit

Returns

mapMap

Map with new unit and converted data

abstract upsample(factor, order=0, preserve_counts=True, axis=None)

Upsample the spatial dimension by a given factor.

Parameters

factorint

Upsampling factor.

orderint

Order of the interpolation used for upsampling.

preserve_countsbool

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).

axisstr

Which axis to upsample. By default spatial axes are upsampled.

Returns

mapMap

Upsampled map.

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

Write to a FITS file.

Parameters

filenamestr

Output file name.

overwritebool

Overwrite existing file?

hdustr

Set the name of the image extension. By default this will be set to SKYMAP (for BINTABLE HDU) or PRIMARY (for IMAGE HDU).

hdu_bandsstr

Set the name of the bands table extension. By default this will be set to BANDS.

formatstr, optional

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). The following formats are supported:

• “gadf” (default)

• “fgst-ccube”

• “fgst-ltcube”

• “fgst-bexpcube”

• “fgst-srcmap”

• “fgst-template”

• “fgst-srcmap-sparse”

• “galprop”

• “galprop2”

sparsebool

Sparsify the map by dropping pixels with zero amplitude. This option is only compatible with the ‘gadf’ format.