New issue 1299: order of parameters set in VR matters https://bitbucket.org/yt_analysis/yt/issues/1299/order-of-parameters-set-in-... Michael Zingale: consider the following script: ``` import yt import numpy as np from yt.visualization.volume_rendering.api import \ Scene, \ VolumeSource # fake test dataset ds = yt.testing.fake_vr_orientation_test_ds(128) # no log please ds._get_field_info("density").take_log = False sc = Scene() vol = VolumeSource(ds, field=('gas', 'density')) sc.add_source(vol) cam = sc.add_camera(ds, lens_type="perspective") cam.resolution = (1280, 720) cam.north_vector = np.array([0., 0., 1.]) cam.focus = ds.arr(np.array([1., 0., 0.]), 'code_length') cam.position = ds.arr(np.array([0., 0., 0.]), 'code_length') #sc.annotate_domain(ds) sc.render() sc.save("test_{:03}.png".format(0), sigma_clip=6.0) ``` this runs as-is. If you change the order of the properties to: ``` cam.north_vector = np.array([0., 0., 1.]) cam.position = ds.arr(np.array([0., 0., 0.]), 'code_length') cam.focus = ds.arr(np.array([1., 0., 0.]), 'code_length') ``` it aborts with ``` RuntimeError: Cannot set the camera focus and position to the same value ``` it you change them to ``` cam.focus = ds.arr(np.array([1., 0., 0.]), 'code_length') cam.position = ds.arr(np.array([0., 0., 0.]), 'code_length') cam.north_vector = np.array([0., 0., 1.]) ``` it aborts with: ``` yt.utilities.exceptions.YTException: normal_vector and north_vector cannot be aligned. ``` these checks should wait until the user is done setting all the properties and the order of setting them should not matter.