New issue 926: cylindrical_radial_velocity does not look right https://bitbucket.org/yt_analysis/yt/issue/926/cylindrical_radial_velocity-d... Suoqing Ji: Recently I just found that ``cylindrical_radial_velocity`` in yt3 does not give me what I expect. To test this, I setup a 3-D Sedov problem with domain ``[-0.5, 0.5]^3`` and explosion center at ``[0, 0, 0]``, and plot the ``cylindrical_radial_velocity`` as the following image. According to the pattern of the velocity streamline, the cylindrical radial velocity should be positive.  I don't understand in the function of ``_cylindrical_radial`` in [yt/fields/vector_operations.py](https://bitbucket.org/yt_analysis/yt/src/1089b61212d7bfd105a109728fb804b6ef8...): ``` #!python def _cylindrical_radial(field, data): normal = data.get_field_parameter("normal") vectors = obtain_rv_vec(data, (xn, yn, zn), "bulk_%s" % basename) theta = resize_vector(data["index", 'cylindrical_theta'], vectors) return get_cyl_r_component(vectors, theta, normal) ``` what does the line of ``resize_vector`` do. If I replace this simply with line ``theta = data['cylindrical_theta']``, it will give the image I expected as the following.  In addition, if I want to plot the same field for a 2-D Sedov dataset, the error of ``yt.utilities.exceptions.YTFieldNotFound: Could not find field '('all', 'cylindrical_radial_velocity')'`` will be raised. However, if changing the line ``` #!python vectors = obtain_rv_vec(data, (xn, yn, zn), "bulk_%s" % basename) ``` into ``` #!python vectors = obtain_rv_vec(data) ``` the correct image will be generated without raising any error. But I'm not very certain what's the correct way to fix this.