Contour.Core.ContourGenerator.MarchingSquares 1.0.6

Contour.Core.ContourGenerator.MarchingSquares

A .NET library for generating contour lines and contour polygons from raster grids using the Marching Squares algorithm. Built on NetTopologySuite geometries and the Contour.Core abstraction layer.

How It Works

Each raster cell (2x2 group of grid nodes) is subdivided into 4 sub-triangles by connecting the corners to a bilinear-interpolated center point. Contour lines and polygons are then traced through this triangle mesh at specified elevation intervals.

TL -------- TR          TL -------- TR
|            |          | \   T    / |
|            |   -->    |  L  +  R   |
|            |          | /   B    \ |
BL -------- BR          BL -------- BR

Installation

dotnet add package Contour.Core.ContourGenerator.MarchingSquares

Usage

From an ESRI ASCII Raster file

using AsciiRaster.Parser;
using Contour.Core.ContourGenerator.MarchingSquares;

// Parse the raster file
var raster = EsriAsciiRaster.Read("elevation.asc");

// Build the triangle mesh
var grid = RasterGrid.FromRaster(raster);

// Create the generator
var generator = new ContourGenerator(
    new MarchingSquaresContourLines(geometryPrecision),
    new MarchingSquaresContourPolygons(geometryPrecision));

generator.SetInput(grid);

// Generate contour lines at 10m intervals
double[] intervals = [10, 20, 30, 40, 50];
Dictionary<double, List<LineString>> contourLines = generator.GenerateContourLines(intervals);

// Generate contour polygons (with optional progress reporting)
Dictionary<double, MultiPolygon> contourPolygons = generator.GenerateContourPolygons(intervals);

From pre-transformed coordinates

When grid coordinates have already been projected or transformed (e.g., to WGS84):

using NetTopologySuite.Geometries;
using Contour.Core.ContourGenerator.MarchingSquares;

// Build a grid from pre-computed nodes [col, row] with M = elevation value
CoordinateM[,] nodes = new CoordinateM[nCols, nRows];
// ... populate nodes ...

var grid = RasterGrid.FromNodes(nodes, noDataValue: -9999);

var generator = new ContourGenerator(
    new MarchingSquaresContourLines(geometryPrecision),
    new MarchingSquaresContourPolygons(geometryPrecision));

generator.SetInput(grid);

Dictionary<double, List<LineString>> lines = generator.GenerateContourLines(intervals);
Dictionary<double, MultiPolygon> polygons = generator.GenerateContourPolygons(intervals);

Key Features

• Contour lines - traces isolines across the triangle mesh at specified elevation intervals
• Contour polygons - generates filled polygons for areas above each contour level, with parallel processing across intervals
• Dual input paths - accepts ESRI ASCII raster files or pre-transformed coordinate arrays
• NoData handling - cells with missing data are excluded from the mesh
• Progress reporting - polygon generation supports IProgress<OperationProgress> for tracking long-running operations

Dependencies

License

MIT - Copyright (c) 2026 Acrotron