## Visualization with yt and Napari Part 2: annotations¶

In this notebook series, we'll continue our exploration of using napari to interactively visualize data loaded and sampled with yt. The first notebook in this series (available here) covered loading both in-memory and dask lazy-loaded yt arrays extracted from Fixed Resolution Regions into napari. In this notebook, we'll explore ways to use napari's point and shape layers to add annotations including Particle Positions and 3D Streamlines

## required packages¶

Running this notebook requires yt and napari in addition to stanard packages from the scipy stack (numpy, matplotlib).

## imports¶

So let's start off by setting up the qt environment needed by napari:

In [1]:
 # for napari, do it first!
%gui qt


and import all the packages we'll use

In [2]:
# general imports
import numpy as np
import matplotlib.pyplot as plt
import os

# yt related
import yt
from yt.units import kpc, Mpc

# napari related imports
import napari
from napari.utils import nbscreenshot


## Test data¶

In this notebook, we'll use the Enzo_64 test dataset (download here, 2.4 Gb). So let's load and slice it, centered on the location of the max density:

In [3]:
ds = yt.load("Enzo_64/DD0043/data0043")
slc = yt.SlicePlot(ds, 'z', 'density', center='m',width=(100,'Mpc'))
slc.show()

yt : [INFO     ] 2020-09-09 09:17:04,459 Parameters: current_time              = 645.81707236914
yt : [INFO     ] 2020-09-09 09:17:04,459 Parameters: domain_dimensions         = [64 64 64]
yt : [INFO     ] 2020-09-09 09:17:04,460 Parameters: domain_left_edge          = [0. 0. 0.]
yt : [INFO     ] 2020-09-09 09:17:04,460 Parameters: domain_right_edge         = [1. 1. 1.]
yt : [INFO     ] 2020-09-09 09:17:04,460 Parameters: cosmological_simulation   = 1
yt : [INFO     ] 2020-09-09 09:17:04,461 Parameters: current_redshift          = 0.0013930880640796
yt : [INFO     ] 2020-09-09 09:17:04,461 Parameters: omega_lambda              = 0.7
yt : [INFO     ] 2020-09-09 09:17:04,461 Parameters: omega_matter              = 0.3
yt : [INFO     ] 2020-09-09 09:17:04,461 Parameters: omega_radiation           = 0.0
yt : [INFO     ] 2020-09-09 09:17:04,462 Parameters: hubble_constant           = 0.71
Parsing Hierarchy : 100%|██████████| 752/752 [00:00<00:00, 9154.52it/s]
yt : [INFO     ] 2020-09-09 09:17:04,563 Gathering a field list (this may take a moment.)
yt : [INFO     ] 2020-09-09 09:17:05,901 max value is 6.27782e-27 at 112568199846666733380173824.0000000000000000 303527266574506220996001792.0000000000000000 62658443770072329458024448.0000000000000000
yt : [INFO     ] 2020-09-09 09:17:05,913 xlim = -0.075093 0.480367
yt : [INFO     ] 2020-09-09 09:17:05,913 ylim = 0.268657 0.824117
yt : [INFO     ] 2020-09-09 09:17:05,914 xlim = -0.075093 0.480367
yt : [INFO     ] 2020-09-09 09:17:05,914 ylim = 0.268657 0.824117
yt : [INFO     ] 2020-09-09 09:17:05,915 Making a fixed resolution buffer of (('gas', 'density')) 800 by 800


In [4]:
slc.center

Out[4]:
[unyt_quantity(0.20263672, 'code_length'),
unyt_quantity(0.54638672, 'code_length')]

## Particle Positions¶

In yt, we we can add particle positions to the slice following the example in the yt docs (link):

In [5]:
slc.annotate_particles((10, 'Mpc'))
slc.show()


But for napari, we'll need to extract that particle position data.

Let's start, by following the previous notebook and pull out a Fixed Resolution Region of the log of the density field into memory and adding it to a napari viewer:

In [6]:
cg = ds.r[::300j,::300j,::300j]
dens_log = np.log10(cg['density'])

In [7]:
viewer = napari.Viewer()
nbscreenshot(viewer)

Out[7]:

Now the question is how do we add our particle positions?

From the napari docs, we have the following example (link) for adding points to an image:

from skimage import data
import napari

viewer = napari.view_image(data.astronaut(), rgb=True)
points = np.array([[100, 100], [200, 200], [300, 100]])
viewer.add_points(points, size=30)

where points is an array with shape (N, D) for N points in D dimensions.

So all we need to do is extract some particle positions and reshape it to an array of the right dimensions.

So let's do just that! Easy enough in yt:

In [8]:
ad = ds.all_data()
particles.shape

Out[8]:
(274305, 3)

Great! We now have our N by D array to add to napari! but wait... these positions are in the code_length of the data set:

In [9]:
ad['particle_position_x'][0]

Out[9]:
unyt_quantity(0.01247314, 'code_length')

but our image's coordinate system is in pixel values so we need to convert our to a pixel coordinate system. Our domain in code_length goes from 0 to 1 in each dimension

In [10]:
print(ds.domain_left_edge)
print(ds.domain_right_edge)

[0. 0. 0.] code_length
[1. 1. 1.] code_length


and we pulled out a 300-pixel image, so we can just multiply the positions by 300:

In [11]:
particles  = particles * 300

In [12]:
viewer.add_points(particles, size=1)
nbscreenshot(viewer)

Out[12]:

Now when we slide through the domain, we also slice through the particle positions:

In [13]:
slc.center

Out[13]:
[unyt_quantity(0.20263672, 'code_length'),
unyt_quantity(0.54638672, 'code_length')]

## 3D Streamlines¶

Napari also has a path shape type that we can use to add 3D streamlines. So let's first calculate some streamlines. Following yt's example streamline notebook, we first define our streamline starting positions as random position within a range of the domain center:

In [14]:
N = 30
c = ds.domain_center
scale = ds.domain_width[0]*.25
pos_dx = np.random.random((N,3))*scale - scale/2
pos = c+pos_dx


Now we create and integrate our streamline object (this step can take a few minutes):

In [15]:
# Create streamlines of the 3D vector velocity and integrate them through
# the box defined above
streamlines = yt.visualization.api.Streamlines(ds, pos, 'velocity_x', 'velocity_y', 'velocity_z',
length=30.0*Mpc, get_magnitude=True)
streamlines.integrate_through_volume()

yt : [INFO     ] 2020-09-09 09:19:38,371 AMRKDTree rebuilt, Final Volume: 1.000000e+00
Streamlining: 100%|██████████| 30/30 [00:00<00:00, 146.70it/s]


The streamlines object now has a list of streamlines in streamlines.streamlines. To access the first 5 positions of the the first streamline:

In [16]:
streamlines.streamlines[0][:5]

Out[16]:
unyt_array([[0.462263  , 0.6093524 , 0.59120923],
[0.46132888, 0.60927614, 0.59094234],
[0.46039483, 0.60920003, 0.59067515],
[0.45946082, 0.60912416, 0.59040776],
[0.45852679, 0.6090486 , 0.59014033]], 'code_length')

To add to napari, we can use the viewer.add_shapes with a shape_type of line, but first we once again need to convert to pixel coordinates

In [17]:
streamlines.streamlines = streamlines.streamlines * 300


and then add to the viewer with add_shapes (we'll also switch to a 3D view):

In [18]:
viewer.add_shapes(streamlines.streamlines, shape_type='path', edge_width=1, edge_color=['white'])
viewer.dims.ndisplay = 3
nbscreenshot(viewer)

Out[18]: