Release: | 1.8.1 |
---|---|

Date: | 3rd June 2015 |

This document explains the new/changed features of Iris in version 1.8.
(*View all changes*.)

Showcase: Rotate winds

Iris can now rotate and unrotate wind vector data by transforming the wind vector data to another coordinate system.

For example:

```
>>> from iris.analysis.cartography import rotate_winds
>>> u_cube = iris.load_cube('my_rotated_u_wind_cube.pp')
>>> v_cube = iris.load_cube('my_rotated_v_wind_cube.pp')
>>> target_cs = iris.coord_systems.GeogCS(6371229.0)
>>> u_prime, v_prime = rotate_winds(u_cube, v_cube, target_cs)
```

Showcase: Nearest-neighbour scheme

A nearest-neighbour scheme for interpolation and regridding has been added
to Iris. This joins the existing `Linear` and
`AreaWeighted` interpolation and regridding schemes.

For example:

```
>>> result = cube.interpolate(sample_points, iris.analysis.Nearest())
>>> regridded_cube = cube.regrid(target_grid, iris.analysis.Nearest())
```

Showcase: Slices over a coordinate

You can slice over one or more dimensions of a cube using `iris.cube.Cube.slices_over()`.
This provides similar functionality to `slices()` but with
almost the opposite outcome.

Using `slices()` to slice a cube on a selected dimension returns
all possible slices of the cube with the selected dimension retaining its dimensionality.
Using `slices_over()` to slice a cube on a selected
dimension returns all possible slices of the cube over the selected dimension.

To demonstrate this:

```
>>> cube = iris.load(iris.sample_data_path('colpex.pp'))[0]
>>> print(cube.summary(shorten=True))
air_potential_temperature / (K) (time: 6; model_level_number: 10; grid_latitude: 83; grid_longitude: 83)
>>> my_slice = next(cube.slices('time'))
>>> my_slice_over = next(cube.slices_over('time'))
>>> print(my_slice.summary(shorten=True))
air_potential_temperature / (K) (time: 6)
>>> print(my_slice_over.summary(shorten=True))
air_potential_temperature / (K) (model_level_number: 10; grid_latitude: 83; grid_longitude: 83)
```

`iris.cube.CubeList.concatenate()`now works with biggus arrays and so now supports concatenation of cubes with deferred data.- Improvements to NetCDF saving through using biggus:

- A cube’s lazy data payload will still be lazy after saving; the data will not be loaded into memory by the save operation.
- Cubes with data payloads larger than system memory can now be saved to NetCDF through biggus streaming the data to disk.

`iris.util.demote_dim_coord_to_aux_coord()`and`iris.util.promote_aux_coord_to_dim_coord()`allow a coordinate to be easily demoted or promoted within a cube.`iris.util.squeeze()`removes all length 1 dimensions from a cube, and demotes any associated squeeze dimension`DimCoord`to be a scalar coordinate.`iris.cube.Cube.slices_over()`, which returns an iterator of all sub-cubes along a given coordinate or dimension index.`iris.cube.Cube.interpolate()`now accepts datetime.datetime and netcdftime.datetime instances for date or time coordinates.- Many new and updated translations between CF spec and STASH codes or GRIB2 parameter codes.
- PP/FF loader creates a height coordinate at 1.5m or 10m for certain relevant stash codes.
- Lazy aggregator support for the
`standard deviation`aggregator has been added. - A speed improvement in calculation of
`iris.analysis.cartography.area_weights()`. - Experimental support for unstructured grids has been added with
`iris.experimental.ugrid()`. This has been implemented using UGRID. `iris.cube.CubeList.extract_overlapping()`supports extraction of cubes over regions where common coordinates overlap, over multiple coordinates.- Warnings raised due to invalid units in loaded data have been suppressed.
- Experimental low-level read and write access for FieldsFile variants is now supported
via
`iris.experimental.um.FieldsFileVariant`. - PP loader will return cubes for all fields prior to a field with a problematic header before raising an exception.
- NetCDF loader skips invalid global attributes, raising a warning rather than raising an exception.
- A warning is now raised rather than an exception when constructing an
`AuxCoordFactory`fails. - Supported
`aux coordinate factories`have been extended to include:

ocean sigma coordinate,ocean s coordinate,ocean s coordinate, generic form 1, andocean s coordinate, generic form 2.

`iris.cube.Cube.intersection()`now supports taking a points-only intersection. Any bounds on intersected coordinates are ignored but retained.- The FF loader’s known handled grids now includes
`Grid 21`. - A
`nearest neighbour`scheme is now provided for`iris.cube.Cube.interpolate()`and`iris.cube.Cube.regrid()`. `iris.analysis.cartography.rotate_winds()`supports transformation of wind vectors to a different coordinate system.- NumPy universal functions can now be applied to cubes using
`iris.analysis.maths.apply_ufunc()`. - Generic functions can be applied to
`Cube`instances using`iris.analysis.maths.IFunc`. - The
`iris.analysis.Linear`scheme now supports regridding as well as interpolation. This enables`iris.cube.Cube.regrid()`to perform bilinear regridding, which now replaces the experimental routine “iris.experimental.regrid.regrid_bilinear_rectilinear_src_and_grid”.

- Fix in netCDF loader to correctly determine whether the longitude coordinate (including scalar coordinates) is circular.
`iris.cube.Cube.intersection()`now supports bounds that extend slightly beyond 360 degrees.- Lateral Boundary Condition (LBC) type FieldFiles are now handled correctly by the FF loader.
- Making a copy of a scalar cube with no data now correctly copies the data array.
- Height coordinates in NAME trajectory output files have been changed to match other NAME output file formats.
- Fixed datatype when loading an
`integer_constants`array from a FieldsFile. - FF/PP loader adds appropriate cell methods for
`lbtim.ib = 3`intervals. - An exception is raised if the units of the latitude and longitude coordinates
of the cube passed into
`iris.analysis.cartography.area_weights()`are not convertible to radians. - GRIB1 loader now creates a time coordinate for a time range indicator of 2.
- NetCDF loader now loads units that are empty strings as dimensionless.

- The PP loader now carefully handles floating point errors in date time conversions to hours.
- The handling fill values for lazy data loaded from NetCDF files is altered, such that the _FillValue set in the file is preserved through lazy operations.
- The risk that cube intersections could return incorrect results due to floating point tolerances is reduced.
- The new GRIB2 loading code is altered to enable the loading of various data representation templates; the data value unpacking is handled by the GRIB API.
- Saving cube collections to NetCDF, where multiple similar aux-factories exist within the cubes, is now carefully handled such that extra file variables are created where required in some cases.

- A fix to prevent the error:
*AttributeError: ‘module’ object has no attribute ‘date2num’*. This was caused by the function`netcdftime.date2num()`being removed from the netCDF4 package in recent versions.

- The original GRIB loader has been deprecated and replaced with a new template-based GRIB loader.
- Deprecated default NetCDF save behaviour of assigning the outermost
dimension to be unlimited. Switch to the new behaviour with no auto
assignment by setting
`iris.FUTURE.netcdf_no_unlimited`to True. - The former experimental method
“iris.experimental.regrid.regrid_bilinear_rectilinear_src_and_grid” has been removed, as
`iris.analysis.Linear`now includes this functionality.

- A chapter on
*merge and concatenate*has been added to the*user guide*. - A section on installing Iris using conda has been
added to the
*install guide*. - Updates to the chapter on
*regridding and interpolation*have been added to the*user guide*.