5. gridData.core
— Core functionality for storing nD grids¶
The core
module contains classes and functions that are
independent of the grid data format. In particular this module
contains the Grid
class that acts as a universal constructor
for specific formats:
g = Grid(**kwargs) # construct
g.export(filename, format) # export to the desired format
Some formats can also be read:
g = Grid() # make an empty Grid
g.load(filename) # populate with data from filename
5.1. Classes and functions¶

class
gridData.core.
Grid
(grid=None, edges=None, origin=None, delta=None, metadata={}, interpolation_spline_order=3, file_format=None)[source]¶ Class to manage a multidimensional grid object.
The export(format=’dx’) method always exports a 3D object, the rest should work for an array of any dimension.
The grid (Grid.grid) can be manipulated as a standard numpy array.
The attribute Grid.metadata holds a userdefined dictionary that can be used to annotate the data. It is saved with save().
Create a Grid object from data.
From a numpy.histogramdd():
grid,edges = numpy.histogramdd(...) g = Grid(grid,edges=edges)
From an arbitrary grid:
g = Grid(grid,origin=origin,delta=delta)
From a saved file:
g = Grid(filename)
or
g = Grid() g.load(filename)
 Arguments
 grid
histogram or density, defined on numpy nD array, or filename
 edges
list of arrays, the lower and upper bin edges along the axes (both are output by numpy.histogramdd())
 origin
cartesian coordinates of the center of grid[0,0,…,0]
 delta
Either n x n array containing the cell lengths in each dimension, or n x 1 array for rectangular arrays.
 metadata
a user defined dictionary of arbitrary values associated with the density; the class does not touch metadata[] but stores it with save()
 interpolation_spline_order
order of interpolation function for resampling; cubic splines = 3 [3]
 file_format
file format; only necessary when
grid
is a filename (seeGrid.load()
); default isNone
and the file format is autodetected.
Changed in version 0.5.0: New file_format keyword argument.

check_compatible
(other)[source]¶ Check if other can be used in an arithmetic operation.
other is a scalar
other is a grid defined on the same edges
 Raises
TypeError
if not compatible.

export
(filename, file_format=None, type=None, typequote='"')[source]¶ export density to file using the given format.
The format can also be deduced from the suffix of the filename though the format keyword takes precedence.
The default format for export() is ‘dx’. Use ‘dx’ for visualization.
Implemented formats:
 dx
OpenDX
 pickle
pickle (use
Grid.load()
to restore);Grid.save()
is simpler thanexport(format='python')
.
 Parameters
filename (str) – name of the output file
file_format ({'dx', 'pickle', None} (optional)) – output file format, the default is “dx”
type (str (optional)) –
for DX, set the output DX array type, e.g., “double” or “float”. By default (
None
), the DX type is determined from the numpy dtype of the array of the grid (and this will typically result in “double”).New in version 0.4.0.
typequote (str (optional)) –
For DX, set the character used to quote the type string; by default this is a doublequote character, ‘”’. Custom parsers like the one from NAMDGridForces (backend for MDFF) expect no quotes, and typequote=’’ may be used to appease them.
New in version 0.5.0.

interpolated
¶ Bspline function over the data grid(x,y,z).
The
interpolated()
function allows one to obtain data values for any values of the coordinates:interpolated([x1,x2,...],[y1,y2,...],[z1,z2,...]) > F[x1,y1,z1],F[x2,y2,z2],...
The interpolation order is set in
Grid.interpolation_spline_order
.The interpolated function is computed once and is cached for better performance. Whenever
interpolation_spline_order
is modified,Grid.interpolated()
is recomputed.The value for unknown data is set in
Grid.interpolation_cval
(TODO: also recompute wheninterpolation_cval
value is changed.)Example
Example usage for resampling:
XX, YY, ZZ = numpy.mgrid[40:75:0.5, 96:150:0.5, 20:50:0.5] FF = interpolated(XX, YY, ZZ)
Note
Values are interpolated with a spline function. It is possible that the spline will generate values that would not normally appear in the data. For example, a density is nonnegative but a cubic spline interpolation can generate negative values, especially at the boundary between 0 and high values.

interpolation_spline_order
¶ Order of the Bspline interpolation of the data.
3 = cubic; 4 & 5 are also supported
Only choose values that are acceptable to
scipy.ndimage.spline_filter()
!See also

load
(filename, file_format=None)[source]¶ Load saved (pickled or dx) grid and edges from <filename>.pickle
Grid.load(<filename>.pickle) Grid.load(<filename>.dx)
The load() method calls the class’s constructor method and completely resets all values, based on the loaded data.

resample
(edges)[source]¶ Resample data to a new grid with edges edges.
This method creates a new grid with the data from the current grid resampled to a regular grid specified by edges. The order of the interpolation is set by
Grid.interpolation_spline_order
: change the value before callingresample()
. Parameters
edges (tuple of arrays or Grid) – edges of the new grid or a
Grid
instance that providesGrid.edges
 Returns
a new
Grid
with the data interpolated over the new grid cells Return type
Examples
Providing edges (a tuple of three arrays, indicating the boundaries of each grid cell):
g = grid.resample(edges)
As a convenience, one can also supply another
Grid
as the argument for this methodg = grid.resample(othergrid)
and the edges are taken from
Grid.edges
.

resample_factor
(factor)[source]¶ Resample to a new regular grid.
 Parameters
factor (float) – The number of grid cells are scaled with factor in each dimension, i.e.,
factor * N_i
cells along each dimension i. Returns
 Return type
See also

save
(filename)[source]¶ Save a grid object to <filename>.pickle
Internally, this calls
Grid.export(filename, format="python")
. A grid can be regenerated from the saved data withg = Grid(filename="grid.pickle")
Note
The pickle format depends on the Python version and therefore it is not guaranteed that a grid saved with, say, Python 2.7 can also be read with Python 3.5. The OpenDX format is a better alternative for portability.

gridData.core.
ndmeshgrid
(*arrs)[source]¶ Return a mesh grid for N dimensions.
The input are N arrays, each of which contains the values along one axis of the coordinate system. The arrays do not have to have the same number of entries. The function returns arrays that can be fed into numpy functions so that they produce values for all points spanned by the axes arrs.
Original from http://stackoverflow.com/questions/1827489/numpymeshgridin3d and fixed.