Open3d: Visualize mesh normals

[ndrplz]

I'm a bit struggling to understand how to get to a visualization similar to this one but for a mesh instead of a point cloud.

Currently what I'm doing is the following:

mesh = read_triangle_mesh("knot.ply")
mesh.compute_vertex_normals()
mesh.vertex_colors = mesh.vertex_normals
draw_geometries([mesh])

which outputs the following:

Is it correct / is there a more principled way to do it?

Thank you.
Andrea

[qianyizh]

The easiest way to mimic point cloud normal rendering behavior is to press ctrl+9 to enable normal rendering for mesh (for point cloud it is 9).

[ndrplz]

Thanks, that's what I meant. However, I'd like to toggle this mode automatically.

Currently as a workaround I'm using

opt = vis.get_render_option().load_from_json("renderoption.json")

where in renderoption.json among other options I have

 `mesh_color_option` : 9  # normal rendering

(for future readers, mesh color options are here).

Still, I tried to do something like

    opt = vis.get_render_option()
    opt.mesh_color_option = 9

but it doesn't seem to like it.

[qianyizh]

Yeah, it is not exposed right now. The current workaround is to use load_from_json.
In the next restructure (hopefully coming soon) we will expose as many APIs in Python as possible.

[ndrplz]

Cool thanks!

[ndrplz]

Re-opening the issue for a strictly related thing. If I set the mesh_color option in the json to either:

mesh_color_option : 2
mesh_color_option : 3
mesh_color_option : 4

I expect to see the rendering of X, Y and Z heatmaps respectively (analogously to what happens with ctrl+2/3/4). However this doesn't happen. Do I miss something?

[syncle]

Thanks for the feedback @ndrplz. Let me work on this.

[syncle]

I just pushed a new PR for this.

The following code

from open3d import *

geometry = read_triangle_mesh("TestData/knot.ply")
geometry.compute_vertex_normals()
print(geometry)

vis = Visualizer()
vis.create_window()
vis.add_geometry(geometry)
vis.get_render_option().mesh_color_option = MeshColorOption.Normal
vis.run()
vis.destroy_window()

should produce this:

[syncle]

FYI, this fix will be shipped with 0.5 release.