New issue 1304: Boolean objects only inherit the fields present in both of their parent objects https://bitbucket.org/yt_analysis/yt/issues/1304/boolean-objects-only-inheri... chummels: Boolean objects are meant to combine the fields present in two data objects from the same dataset. Normally, this means that they will have the same fields present. However, the `ray` object creates a special field `"t"` as a parametric variable to tell you how far along the ray you are (goes from 0 to 1). When I take an intersection of this `ray` object with a `region` object, the result lacks this `"t"` field because `"t"` is only present in a single parent in the boolean intersection. Here is an example of this in action with a sample dataset: import yt import numpy as np ds = yt.load("gizmo_cosmology_plus/snap_N128L16_151.hdf5") ad = ds.all_data() ad[('gas', 'temperature')] ray_start = ds.arr(np.random.random(3), 'unitary') ray_end = ds.arr(np.random.random(3), 'unitary') ray1 = ds.ray(ray_start, ray_end) ray2 = ray1 & ad # ray1 object *has* a t field because it was created from scratch print ray1['t'] # ray2 object *lacks* a t field because only one of its parents contains it print ray2['t']