Iris: cube.intersection out of bounds point

[trexfeathers]

Example: when the upper bound of a point_x is at 0, the following code returns point_x, instead of wrapping the point to 360-point_x:
target_grid.intersection(iris.coords.CoordExtent('longitude', 0, 360))

[valeriupredoi]

we have noticed this too, here is a minimal example that reproduces the problem hassle-free:

import iris
import numpy as np

lon_points = np.array([-8.75, -6.25, -3.75, -1.25,  1.25,  3.75,  6.25,  8.75, 11.25,
                       13.75, 16.25, 18.75, 21.25, 23.75, 26.25, 28.75, 31.25, 33.75,
                       36.25, 38.75])
lon_bounds = np.array([[ -2.5,   0. ], [  0. ,   2.5],
    [  2.5,   5. ], [  5. ,   7.5],
    [  7.5,  10. ], [ 10. ,  12.5],
    [ 12.5,  15. ], [ 15. ,  17.5],
    [ 17.5,  20. ], [ 20. ,  22.5],
    [ 22.5,  25. ], [ 25. ,  27.5],
    [ 27.5,  30. ], [ 30. ,  32.5],
    [ 32.5,  35. ], [ 35. ,  37.5],
    [ 37.5,  40. ], [350. , 352.5],
    [352.5, 355. ], [355. , 357.5]])
lons = iris.coords.DimCoord(lon_points, standard_name='longitude', bounds=lon_bounds,
                            units='degrees_east')
cube = iris.cube.Cube(np.zeros((20,)), dim_coords_and_dims=[(lons, 0)])
isect_with_bounds = cube.intersection(longitude=(0, 360))
print(isect_with_bounds.coord("longitude"))
cube.coord("longitude").bounds = None
isect_without_bounds = cube.intersection(longitude=(0, 360))
print(isect_without_bounds.coord("longitude"))
cube.coord("longitude").guess_bounds()
isect_guessbounds = cube.intersection(longitude=(0, 360))
print(isect_guessbounds.coord("longitude"))

• with bounds I get a negative point where should be none;
• removing the bounds I get the correct result;
• reintroducing the bounds by guessing them, the undesired behavior is seen again

@bjlittle @pelson @lbdreyer what you guys reckon? Muchos cheers :beer:

[valeriupredoi]

just a heads up that the behavior is exactly the same as described above for iris=3.0.1 too so the issue still stands, friendly ping to @bjlittle @lbdreyer :+1: :beer:

[rcomer]

I think I can see how to fix this. Will unassign myself if I'm wrong!

[valeriupredoi]

cheers muchly @rcomer :beer:

[rcomer]

Now fixed in v3.0.x by #4059