Modifying mesh interactively in Dash

Dash Python
1

Hi all,

First of all, thanks for creating Dash. It is very useful.

What I am trying to do is use Dash to do some mesh manipulations interactively. The mesh is in obj format and so I decided to use dash-vtk. I started with the demo apps and could do simple reading and visualization. But when I try to, for example, scale it, the mesh just disappears.

Here’s the code I used. I used the slider to control the scale factor.

import dash
import dash_vtk
import dash_bootstrap_components as dbc
import dash_html_components as html
import dash_core_components as dcc
from dash.dependencies import Input, Output

from pyvista import examples
from vtk.util.numpy_support import vtk_to_numpy

# Get point cloud data from PyVista
uniformGrid = examples.download_crater_topo()
subset = uniformGrid.extract_subset((500, 900, 400, 800, 0, 0), (5, 5, 1))


def updateWarp(factor=1):
    terrain = subset.warp_by_scalar()
    polydata = terrain.extract_geometry()
    points = polydata.points.ravel() * factor
    polys = vtk_to_numpy(polydata.GetPolys().GetData())
    return (points, polys)


points, polys = updateWarp(1)

# Setup VTK rendering of PointCloud
app = dash.Dash(__name__, external_stylesheets=[dbc.themes.BOOTSTRAP])
server = app.server

vtk_view = dash_vtk.View(
    id="vtk-view",
    children=[
        dash_vtk.GeometryRepresentation(
            id="vtk-representation",
            children=[
                dash_vtk.PolyData(
                    id="vtk-polydata",
                    points=points,
                    polys=polys,
                )
            ],
        ),
    ],
)

app.layout = dbc.Container(
    fluid=True,
    style={"height": "100vh"},
    children=[
        dbc.Row(
            [
                dbc.Col(
                    children=dcc.Slider(
                        id="scale-factor",
                        min=0.1,
                        max=5,
                        step=0.1,
                        value=1,
                        marks={0.1: "0.1", 5: "5"},
                    )
                ),
            ],
            style={"height": "12%", "alignItems": "center"},
        ),
        html.Div(
            html.Div(vtk_view, style={"height": "100%", "width": "100%"}),
            style={"height": "88%"},
        ),
    ],
)


@app.callback(
    [
        Output("vtk-polydata", "points"),
        Output("vtk-polydata", "polys"),
    ],
    [
        Input("scale-factor", "value"),
    ],
)
def updatePresetName(scale_factor):
    points, polys = updateWarp(scale_factor)
    return (
        points,
        polys,
    )


if __name__ == "__main__":
    app.run_server(debug=True)