visualizing_3d_skeletons.md

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# Display 3D skeletons in napari

There are two ways to display 3D skeletons in napari. First, we demonstrate how to use the napari Shapes layer to draw Paths for each skeleton path. As of napari 0.4.14, however, 3D interactivity in the Shapes layer is not ideal, so we also demonstrate how to use the Labels layer.

+++

## Using the Shapes layer

The napari Shapes layer allows displaying of 2D and 3D paths, and coloring them by tabular properties, which makes it ideal for displaying skeletons, and the measurements provided by skan.

```{code-cell} ipython3
import napari
import numpy as np
import skan
from skimage.data import binary_blobs
from skimage.morphology import skeletonize
import scipy.ndimage as ndi
```

```{note}
We use synthetic data here. If you have a cool 3D skeleton dataset that you'd like to show off in these docs, let us know!
```

```{code-cell} ipython3
blobs = binary_blobs(64, volume_fraction=0.3, n_dim=3)
binary_skeleton = skeletonize(blobs)
skeleton = skan.Skeleton(binary_skeleton)
```

```{code-cell} ipython3
all_paths = [
        skeleton.path_coordinates(i)
        for i in range(skeleton.n_paths)
        ]
```

```{code-cell} ipython3
paths_table = skan.summarize(skeleton, separator='_')
```

```{code-cell} ipython3
paths_table['path_id'] = np.arange(skeleton.n_paths)
```

First, we color by random path ID, showing each path in a distinct color using the matplotlib "tab10" qualitative palette. (Coloring by path ID directly results in "bands" of nearby paths receiving the same color.)

```{code-cell} ipython3
paths_table['random_path_id'] = np.random.default_rng().permutation(skeleton.n_paths)
```

```{code-cell} ipython3
viewer = napari.Viewer(ndisplay=3)

skeleton_layer = viewer.add_shapes(
        all_paths,
        shape_type='path',
        properties=paths_table,
        edge_width=0.5,
        edge_color='random_path_id',
        edge_colormap='tab10',
)
```

```{code-cell} ipython3
:tags: ["remove-input"]
viewer.camera.angles = (-30, 30, -135)
viewer.camera.zoom = 6.5
napari.utils.nbscreenshot(viewer)
```

We can also demonstrate that most of these branches are in one skeleton, with a few stragglers around the edges, by coloring by skeleton ID:

```{code-cell} ipython3
skeleton_layer.edge_color = 'skeleton_id'
# for now, we need to set the face color as well
skeleton_layer.face_color = 'skeleton_id'
```

```{code-cell} ipython3
:tags: ["remove-input"]
viewer.camera.angles = (-30, 30, -135)
napari.utils.nbscreenshot(viewer)
```

Finally, we can color the paths by a numerical property, such as their length.

```{code-cell} ipython3
skeleton_layer.edge_color = 'branch_distance'
skeleton_layer.edge_colormap = 'viridis'
# for now, we need to set the face color as well
skeleton_layer.face_color = 'branch_distance'
skeleton_layer.face_colormap = 'viridis'
```

```{code-cell} ipython3
:tags: [remove-input]

viewer.camera.angles = (-30, 30, -135)
napari.utils.nbscreenshot(viewer)
```