labelmap-polydata

Convert vtk.js labelmap ImageData to PolyData meshes using marching cubes.

Installation

npm install labelmap-polydata

Requires @kitware/vtk.js as a peer dependency.

Usage

import { labelmapToPolyDatas } from "labelmap-polydata/labelmapToPolyDatas";

// Create or load a labelmap ImageData where voxel values
// represent segment IDs (0 = background)
const labelmap: vtkImageData = /* your labelmap */;

// Convert to polydata meshes (runs on main thread)
const polyDatas = await labelmapToPolyDatas(labelmap);

// Result is a record mapping segment values to vtkPolyData
for (const [segmentValue, polyData] of Object.entries(polyDatas)) {
  console.log(`Segment ${segmentValue}: ${polyData.getNumberOfPoints()} points`);
}

Web Worker Support

For non-blocking conversion, create a worker file in your project. This lets your bundler resolve vtk.js, so you control the version.

1. Create a worker file in your project:

// src/workers/labelmapWorker.ts
import { handleLabelmapMessage } from "labelmap-polydata/workerHandler";

self.onmessage = (e) => {
  const { result, transferables } = handleLabelmapMessage(e.data);
  self.postMessage({ result }, transferables);
};

2. Use the worker:

import { labelmapToPolyDatas } from "labelmap-polydata/labelmapToPolyDatas";
import LabelmapWorker from "./workers/labelmapWorker?worker";

const worker = new LabelmapWorker();

const polyDatas = await labelmapToPolyDatas(labelmap, { worker });

worker.terminate();

Options

import { labelmapToPolyDatas } from "labelmap-polydata/labelmapToPolyDatas";

const polyDatas = await labelmapToPolyDatas(labelmap, {
  worker: myWorker, // Worker instance for non-blocking execution
  segments: [1, 2, 3], // Process specific segment values (default: all non-zero)
});

World Space Alignment

The marching cubes algorithm outputs polydata in scaled index space (origin + index × spacing) but does not apply the image's direction matrix. For images with non-identity direction (oblique/rotated scans), use buildDirectionMatrix to align the mesh with world space:

import { buildDirectionMatrix } from "labelmap-polydata/directionMatrix";

const directionMatrix = buildDirectionMatrix(labelmap);
actor.setUserMatrix(directionMatrix);

License

MIT