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MapToolkit

README.md

Pmad.Cartography

NuGet License: MIT

A .NET library for Digital Elevation Model (DEM) processing. It provides elevation queries, contour line generation, hillshading and support for multiple data formats and on-demand HTTP data sources.

Installation

dotnet add package Pmad.Cartography

Getting started

Query elevation from a well-known database

// Uses SRTM1 data hosted on cdn.dem.pmad.net (downloaded on demand and cached locally)
var database = WellKnownDatabases.GetSRTM1();

// Single point - bilinear interpolation
var elevation = await database.GetElevationAsync(
    new Coordinates(51.509865, -0.118092),
    DefaultInterpolation.Instance);

// Load an area into memory as a float raster
var area = await database.CreateView<float>(
    new Coordinates(51, -1),
    new Coordinates(52, 0));

Elevation contours

var contour = new ContourGraph();
// 10-metre interval starting at 10 m
contour.Add(area, new ContourLevelGenerator(10, 10));

foreach (var line in contour.Lines)
{
    Console.WriteLine($"Level {line.Level}: {line.Points.Count} points");
}

Hillshading

// Each pixel of 'area' represents a 10x10-metre cell
var hillshader = new HillshaderFast(new Vector2D(10, 10));

// Returns an RGBA image where alpha encodes shadow intensity
Image<Rgba32> img = hillshader.GetPixelsAlphaBelowFlat(area);

Data sources

The following open datasets are pre-configured in WellKnownDatabases:

Source Resolution License Credits
SRTM1 1 arc second Public Domain NASA
SRTM15+ 15 arc seconds Public Domain Tozer et al.
AW3D30 1 arc second See terms (c) JAXA

Data is fetched over HTTP from cdn.dem.pmad.net and cached locally. You can supply a custom cache path:

var database = WellKnownDatabases.GetSRTM1(localCache: @"C:\dem-cache");

File formats

Supported raster formats

Format Read Write Notes
ESRI ASCII Yes Yes float only
DDC Yes Yes Native format for this library
GeoTIFF Yes WGS84 projection only
SRTM HGT Yes 1 and 3 arc-second

Supported compression wrappers

Format Read Write Notes
ZSTD Yes Yes Best storage/CPU trade-off (default)
GZip Yes Yes Lowest CPU cost
Brotli Yes Yes Best compression ratio
Zip Yes Archive must contain a single file

Key types

Type Description
DemDatabase Main entry point - wraps a storage and provides async elevation/view queries
WellKnownDatabases Factory helpers for the pre-configured CDN datasets
DemDataCell<T> In-memory raster tile with typed pixel values
ContourGraph Builds a set of contour lines from a raster view
ContourLevelGenerator Defines the interval and starting elevation for contour generation
HillshaderFast Fast hillshading using the Zevenbergen-Thorne gradient algorithm
HillshaderClassic Reference hillshader (slower, same visual output)
HillshaderIgor Alternative hillshader with a different lighting model
DefaultInterpolation Bilinear elevation interpolation between raster pixels
Coordinates WGS84 latitude/longitude coordinate pair
DemFileSystemStorage Reads a DEM database from a local directory
DemHttpStorage Downloads DEM tiles on demand from an HTTP server with local caching

Dependencies