scipy.ndimage.map_coordinates

scipy.ndimage.map_coordinates(input, coordinates, output=None, order=3, mode='constant', cval=0.0, prefilter=True)

Map the input array to new coordinates by interpolation.

The array of coordinates is used to find, for each point in the output, the corresponding coordinates in the input. The value of the input at those coordinates is determined by spline interpolation of the requested order.

The shape of the output is derived from that of the coordinate array by dropping the first axis. The values of the array along the first axis are the coordinates in the input array at which the output value is found.

Parameters:

input : ndarray

The input array.

coordinates : array_like

The coordinates at which input is evaluated.

output : ndarray or dtype, optional

The array in which to place the output, or the dtype of the returned array.

order : int, optional

The order of the spline interpolation, default is 3. The order has to be in the range 0-5.

mode : str, optional

Points outside the boundaries of the input are filled according to the given mode (‘constant’, ‘nearest’, ‘reflect’ or ‘wrap’). Default is ‘constant’.

cval : scalar, optional

Value used for points outside the boundaries of the input if mode='constant'. Default is 0.0

prefilter : bool, optional

The parameter prefilter determines if the input is pre-filtered with spline_filter before interpolation (necessary for spline interpolation of order > 1). If False, it is assumed that the input is already filtered. Default is True.

Returns:

map_coordinates : ndarray

The result of transforming the input. The shape of the output is derived from that of coordinates by dropping the first axis.

See also

spline_filter, geometric_transform, scipy.interpolate

Examples

>>> from scipy import ndimage
>>> a = np.arange(12.).reshape((4, 3))
>>> a
array([[  0.,   1.,   2.],
       [  3.,   4.,   5.],
       [  6.,   7.,   8.],
       [  9.,  10.,  11.]])
>>> ndimage.map_coordinates(a, [[0.5, 2], [0.5, 1]], order=1)
array([ 2.,  7.])

Above, the interpolated value of a[0.5, 0.5] gives output[0], while a[2, 1] is output[1].

>>> inds = np.array([[0.5, 2], [0.5, 4]])
>>> ndimage.map_coordinates(a, inds, order=1, cval=-33.3)
array([  2. , -33.3])
>>> ndimage.map_coordinates(a, inds, order=1, mode='nearest')
array([ 2.,  8.])
>>> ndimage.map_coordinates(a, inds, order=1, cval=0, output=bool)
array([ True, False], dtype=bool)