WcsGeom

class gammapy.maps.WcsGeom(wcs, npix, cdelt=None, crpix=None, axes=None, cutout_info=None)[source]

Bases: gammapy.maps.Geom

Geometry class for WCS maps.

This class encapsulates both the WCS transformation object and the the image extent (number of pixels in each dimension). Provides methods for accessing the properties of the WCS object and performing transformations between pixel and world coordinates.

Parameters
wcsWCS

WCS projection object

npixtuple

Number of pixels in each spatial dimension

cdelttuple

Pixel size in each image plane. If none then a constant pixel size will be used.

crpixtuple

Reference pixel coordinate in each image plane.

axeslist

Axes for non-spatial dimensions

cutout_infodict

Dict with cutout info, if the WcsGeom was created by WcsGeom.cutout()

Attributes Summary

axes

List of non-spatial axes.

axes_names

center_coord

Map coordinate of the center of the geometry.

center_pix

Pixel coordinate of the center of the geometry.

center_skydir

Sky coordinate of the center of the geometry.

cutout_info

Cutout info dict.

data_shape

Shape of the Numpy data array matching this geometry.

frame

Coordinate system of the projection.

is_allsky

Flag for all-sky maps.

is_flat

Whether the geom non spatial axes have length 1, i.e.

is_hpx

is_image

Whether the geom is an image without extra dimensions.

is_regular

Is this geometry is regular in non-spatial dimensions (bool)?

ndim

npix

Tuple with image dimension in pixels in longitude and latitude.

pixel_area

Pixel area in deg^2.

pixel_scales

Pixel scale.

projection

Map projection.

shape_axes

Shape of non-spatial axes.

wcs

WCS projection object.

width

Tuple with image dimension in deg in longitude and latitude.

Methods Summary

bin_volume()

Bin volume (Quantity)

contains(coords)

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

contains_pix(pix)

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

coord_to_idx(coords[, clip])

Convert map coordinates to pixel indices.

coord_to_pix(coords)

Convert map coordinates to pixel coordinates.

coord_to_tuple(coord)

Generate a coordinate tuple compatible with this geometry.

copy(**kwargs)

Copy and overwrite given attributes.

create([npix, binsz, proj, frame, refpix, …])

Create a WCS geometry object.

crop(crop_width)

Crop the geometry at the edges.

cutout(position, width[, mode])

Create a cutout around a given position.

downsample(factor[, axis])

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

drop(axis)

Drop an axis from the geom.

energy_mask([emin, emax, round_to_edge])

Create a mask for a given energy range.

from_hdulist(hdulist[, hdu, hdu_bands])

Load a geometry object from a FITS HDUList.

from_header(header[, hdu_bands])

Create a WCS geometry object from a FITS header.

get_axis_by_name(name)

Get an axis by name (case in-sensitive).

get_axis_index_by_name(name)

Get an axis index by name (case in-sensitive).

get_coord([idx, flat, mode, frame])

Get map coordinates from the geometry.

get_idx([idx, flat])

Get tuple of pixel indices for this geometry.

get_image_shape(idx)

Get the shape of the image plane at index idx.

get_pix([idx, mode])

Get map pix coordinates from the geometry.

is_aligned(other[, tolerance])

Check if WCS and extra axes are aligned.

make_bands_hdu([hdu, hdu_skymap, conv])

make_header()

pad(pad_width)

Pad the geometry at the edges.

pix_to_coord(pix)

Convert pixel coordinates to map coordinates.

pix_to_idx(pix[, clip])

Convert pixel coordinates to pixel indices.

region_mask(regions[, inside])

Create a mask from a given list of regions

resample_axis(axis)

Resample geom to a new axis binning.

separation(center)

Compute sky separation wrt a given center.

slice_by_idx(slices)

Create a new geometry by slicing the non-spatial axes.

solid_angle()

Solid angle array (Quantity in sr).

squash(axis)

Squash geom axis.

to_binsz(binsz)

Change pixel size of the geometry.

to_cube(axes)

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

to_image()

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

upsample(factor[, axis])

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

Attributes Documentation

axes

List of non-spatial axes.

axes_names
center_coord

Map coordinate of the center of the geometry.

Returns
coordtuple
center_pix

Pixel coordinate of the center of the geometry.

Returns
pixtuple
center_skydir

Sky coordinate of the center of the geometry.

Returns
pixSkyCoord
cutout_info

Cutout info dict.

data_shape

Shape of the Numpy data array matching this geometry.

frame

Coordinate system of the projection.

Galactic (“galactic”) or Equatorial (“icrs”).

is_allsky

Flag for all-sky maps.

is_flat

Whether the geom non spatial axes have length 1, i.e. if the geom is equivalent to an image.

is_hpx = False
is_image

Whether the geom is an image without extra dimensions.

is_regular

Is this geometry is regular in non-spatial dimensions (bool)?

  • False for multi-resolution or irregular geometries.

  • True if all image planes have the same pixel geometry.

ndim
npix

Tuple with image dimension in pixels in longitude and latitude.

pixel_area

Pixel area in deg^2.

pixel_scales

Pixel scale.

Returns angles along each axis of the image at the CRPIX location once it is projected onto the plane of intermediate world coordinates.

Returns
angle: Angle
projection

Map projection.

shape_axes

Shape of non-spatial axes.

wcs

WCS projection object.

width

Tuple with image dimension in deg in longitude and latitude.

Methods Documentation

bin_volume()[source]

Bin volume (Quantity)

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.

contains_pix(pix)

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

Parameters
pixtuple

Tuple of pixel coordinates.

Returns
containmentndarray

Bool array.

coord_to_idx(coords, clip=False)

Convert map coordinates to pixel indices.

Parameters
coordstuple or MapCoord

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.

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.

Returns
pixtuple

Tuple of pixel indices in image and band dimensions. Elements set to -1 correspond to coordinates outside the map.

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.

coord_to_tuple(coord)

Generate a coordinate tuple compatible with this geometry.

Parameters
coordMapCoord
copy(**kwargs)

Copy and overwrite given attributes.

Parameters
**kwargsdict

Keyword arguments to overwrite in the map geometry constructor.

Returns
copyGeom

Copied map geometry.

classmethod create(npix=None, binsz=0.5, proj='CAR', frame='icrs', refpix=None, axes=None, skydir=None, width=None)[source]

Create a WCS geometry object.

Pixelization of the map is set with binsz and one of either npix or width arguments. For maps with non-spatial dimensions a different pixelization can be used for each image plane by passing a list or array argument for any of the pixelization parameters. If both npix and width are None then an all-sky geometry will be created.

Parameters
npixint or tuple or list

Width of the map in pixels. A tuple will be interpreted as parameters for longitude and latitude axes. For maps with non-spatial dimensions, list input can be used to define a different map width in each image plane. This option supersedes width.

widthfloat or tuple or list

Width of the map in degrees. A tuple will be interpreted as parameters for longitude and latitude axes. For maps with non-spatial dimensions, list input can be used to define a different map width in each image plane.

binszfloat or tuple or list

Map pixel size in degrees. A tuple will be interpreted as parameters for longitude and latitude axes. For maps with non-spatial dimensions, list input can be used to define a different bin size in each image plane.

skydirtuple 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.

frame{“icrs”, “galactic”}, optional

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

axeslist

List of non-spatial axes.

projstring, optional

Any valid WCS projection type. Default is ‘CAR’ (cartesian).

refpixtuple

Reference pixel of the projection. If None this will be set to the center of the map.

Returns
geomWcsGeom

A WCS geometry object.

Examples

>>> from gammapy.maps import WcsGeom
>>> from gammapy.maps import MapAxis
>>> axis = MapAxis.from_bounds(0,1,2)
>>> geom = WcsGeom.create(npix=(100,100), binsz=0.1)
>>> geom = WcsGeom.create(npix=[100,200], binsz=[0.1,0.05], axes=[axis])
>>> geom = WcsGeom.create(width=[5.0,8.0], binsz=[0.1,0.05], axes=[axis])
>>> geom = WcsGeom.create(npix=([100,200],[100,200]), binsz=0.1, 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, mode='trim')[source]

Create a cutout around a given position.

Parameters
positionSkyCoord

Center position of the cutout region.

widthtuple of Angle

Angular sizes of the region in (lon, lat) in that specific order. If only one value is passed, a square region is extracted.

mode{‘trim’, ‘partial’, ‘strict’}

Mode option for Cutout2D, for details see Cutout2D.

Returns
cutoutWcsNDMap

Cutout map

downsample(factor, axis=None)[source]

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

Parameters
factorint

Downsampling factor.

axisstr

Axis to downsample.

Returns
geomGeom

Downsampled geometry.

drop(axis)

Drop an axis from the geom.

Parameters
axisstr

Name of the axis to remove.

Returns
geomGeom

New geom with the axis removed.

energy_mask(emin=None, emax=None, round_to_edge=False)

Create a mask for a given energy range.

The energy bin must be fully contained to be included in the mask.

Parameters
emin, emaxQuantity

Energy range

Returns
maskndarray

Energy mask

classmethod from_hdulist(hdulist, hdu=None, hdu_bands=None)

Load a geometry object from a 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. If not defined this will be inferred from the FITS header of the map HDU.

Returns
geomGeom

Geometry object.

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

Create a WCS geometry object from a FITS header.

Parameters
headerHeader

The FITS header

hdu_bandsBinTableHDU

The BANDS table HDU.

Returns
wcsWcsGeom

WCS geometry object.

get_axis_by_name(name)

Get an axis by name (case in-sensitive).

Parameters
namestr

Name of the requested axis

Returns
axisMapAxis

Axis

get_axis_index_by_name(name)

Get an axis index by name (case in-sensitive).

Parameters
namestr

Axis name

Returns
indexint

Axis index

get_coord(idx=None, flat=False, mode='center', frame=None)[source]

Get map coordinates from the geometry.

Parameters
mode{‘center’, ‘edges’}

Get center or edge coordinates for the spatial axes.

Returns
coordMapCoord

Map coordinate object.

get_idx(idx=None, flat=False)[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.

localbool

Flag to return local or global pixel indices. Local indices run from 0 to the number of pixels in a given image plane.

flatbool, optional

Return a flattened array containing only indices for pixels contained in the geometry.

Returns
idxtuple

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

get_image_shape(idx)[source]

Get the shape of the image plane at index idx.

get_pix(idx=None, mode='center')[source]

Get map pix coordinates from the geometry.

Parameters
mode{‘center’, ‘edges’}

Get center or edge pix coordinates for the spatial axes.

Returns
coordtuple

Map pix coordinate tuple.

is_aligned(other, tolerance=1e-06)[source]

Check if WCS and extra axes are aligned.

Parameters
otherWcsGeom

Other geom.

tolerancefloat

Tolerance for the comparison.

Returns
alignedbool

Whether geometries are aligned

make_bands_hdu(hdu=None, hdu_skymap=None, conv=None)
make_header()[source]
pad(pad_width)[source]

Pad the geometry at the edges.

Parameters
pad_width{sequence, array_like, int}

Number of values padded to the edges of each axis.

Returns
geomGeom

Padded geometry.

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 of 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.

Returns
idxtuple

Tuple of pixel indices.

region_mask(regions, inside=True)[source]

Create a mask from a given list of regions

Parameters
regionslist of Region

Python list of regions (pixel or sky regions accepted)

insidebool

For inside=True, pixels in the region to True (the default). For inside=False, pixels in the region are False.

Returns
mask_mapndarray of boolean type

Boolean region mask

Examples

Make an exclusion mask for a circular region:

from regions import CircleSkyRegion
from astropy.coordinates import SkyCoord, Angle
from gammapy.maps import WcsNDMap, WcsGeom

pos = SkyCoord(0, 0, unit='deg')
geom = WcsGeom.create(skydir=pos, npix=100, binsz=0.1)

region = CircleSkyRegion(
    SkyCoord(3, 2, unit='deg'),
    Angle(1, 'deg'),
)
mask = geom.region_mask([region], inside=False)

Note how we made a list with a single region, since this method expects a list of regions.

The return mask is a boolean Numpy array. If you want a map object (e.g. for storing in FITS or plotting), this is how you can make the map:

mask_map = WcsNDMap(geom=geom, data=mask)
mask_map.plot()
resample_axis(axis)

Resample geom to a new axis binning.

This method groups the existing bins into a new binning.

Parameters
axisMapAxis

New map axis.

Returns
mapGeom

Geom with resampled axis.

separation(center)[source]

Compute sky separation wrt a given center.

Parameters
centerSkyCoord

Center position

Returns
separationAngle

Separation angle array (2D)

slice_by_idx(slices)

Create a new geometry by slicing the non-spatial axes.

Parameters
slicesdict

Dict of axes names and integers or slice object pairs. Contains one element for each non-spatial dimension. For integer indexing the correspoding axes is dropped from the map. Axes not specified in the dict are kept unchanged.

Returns
geomGeom

Sliced geometry.

solid_angle()[source]

Solid angle array (Quantity in sr).

The array has the same dimension as the WcsGeom object.

To return solid angles for the spatial dimensions only use:

WcsGeom.to_image().solid_angle()
squash(axis)

Squash geom axis.

Parameters
axisstr

Axis to squash.

Returns
geomGeom

Geom with squashed axis.

to_binsz(binsz)[source]

Change pixel size of the geometry.

Parameters
binszfloat or tuple or list

New pixel size 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_image()[source]

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

Returns
geomGeom

Image geometry.

upsample(factor, axis=None)[source]

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

Parameters
factorint

Upsampling factor.

axisstr

Axis to upsample.

Returns
geomGeom

Upsampled geometry.