wasm-marching-squares

This library is a direct port of rveciana's raster-marching-squares to WebAssembly by way of C. The algorithm is implemented in C and currently generates GeoJSON isolines given raw data from a GeoTIFF file. Isobands will be supported in the future.

Usage

Import the library; import loadWasmMarchingSquaresModule from 'wasm-marching-squares';

Load the WASM library asyncronously: const WasmMarchingSquares = await loadWasmMarchingSquaresModule();

Create some isolines!

/**
 * rasterMatrix: number[][]
 * intervals: number[]
 * transform: number[] (six values -> please see https://gdal.org/user/raster_data_model.html#affine-geotransform)
 **/
const isolines = WasmMarchingSquares.generateIsolines(rasterMatrix, intervals, transform);

Caveats

• Need to add a cleaner external API for ease of use.
• Isoband generation is not implemented yet

Build

To properly build, you will need to download the Emscripten SDK.

1. Compile the Jansson C JSON library using emcc

   • Remove CMakeCache.txt from `include/jansson-2.13.1 if it exists
   • cd include/jansson-2.13.1 && emcmake cmake -DCMAKE_INSTALL_PREFIX:PATH=./emcc-lib .
   • emmake make VERBOSE=1
   • emmake make check
   • emmake make install

2. Generate the WASM code and JavaScript 'glue' code

./build

Test

C Library Unit Testing

1. Compile the Jansson C JSON library using cmake

   • Remove CMakeCache.txt from `include/jansson-2.13.1 if it exists
   • cd include/jansson-2.13.1 && cmake .
   • emmake make VERBOSE=1
   • emmake make check
   • emmake make install

2. Compile and run the unit tests

cd test && ./test

Functional Testing

• Start a webserver and serve the test directory
• Navigate to the index.html and click Test GeoJSON
• You can test the vardah.tif file or the sfctmp.tif file by altering the test/map.js file.

TODO

• Implement Isoband generation
• Speed up lookups using a Quadtree