srtm-elevation

This node module is based in node-hgt so thank you perliedman!

This module read and query HGT files after cache them from NASA's server, for elevation data with high performance.

BREAKING CHANGES IN v2.0.0!

Since January 2021, you must authenticate in order to access the EarthData NASA elevation data.

If you do not have an Earthdata Login, create one at https://urs.earthdata.nasa.gov/users/new.

After activate the account you must specify your username and password when you instantiate the class SyncTileSet:

    var tileset = new SyncTileSet('./data/', [57, 11], [58, 12], function(err) {
        ...
    }, {
        username: 'XXX',
        password: 'XXX'
    });

Install

npm install --save srtm-elevation

Usage

Load and query a HGT file:

    var hgt = new Hgt(__dirname + '/data/N57E011.hgt', [57, 11]);
    
    // Return elevation in meters above sea level.
    // By default, elevation is interpolated bilinearly.
    hgt.getElevation([57, 11])

Use a cache directory of HGT files for querying. Missing data will be downloaded using the elevation data from EarthData NASA's server, by default.

    var tileset = new TileSet('./data/');
    tileset.getElevation([57.7, 11.9], function(err, elevation) {
        if (err) {
            console.log('getElevation failed: ' + err.message);
        } else {
            console.log(elevation);
        }
    });

There's also a synchronous tile set, if you know before hand which area you will query:

    var tileset = new SyncTileSet('./data/', [57, 11], [58, 12], function(err) {
        if (err) {
            console.log(err);
            return;
        }

        // All tiles are loaded (or downloaded, if they were not already on disk)
        // and queries can be made synchronous.

        var elevation = tileset.getElevation([57.7, 11.9]);
        console.log(elevation);
    }, {
        username: 'XXX',
        password: 'XXX'
    });

Full example

In this example, we have an array of locations with a route from Madrid to Paris. We determine the bounds by calculating the minimum and maximum latitude and longitude. The SyncTileSet function will retrieve the necessary hgt files from the NASA's server and will cache it. In the callback we calculate the elevation of each point.

The first call will take longer because we have to download and unzip the .hgt.zip files, the following calls will be faster because the files have been cached.

    var SyncTileSet = require('./src').SyncTileSet;

    // From Madrid to Paris [ latitude, longitude ]
    let locations = [
        [ 40.396764305572056, -3.7408447265625004  ],
        [ 44.465151013519645,  2.2467041015625004  ],
        [ 43.23319741022136 , -2.9278564453125     ],
        [ 43.337164854911094, -1.4337158203125     ],
        [ 44.84418558537004 , -0.6207275390625001  ],
        [ 46.5739667965278  ,  0.36254882812500006 ],
        [ 47.87214396888731 ,  1.9006347656250002  ],
        [ 48.850258199721495,  2.3291015625000004  ]
    ];

    // Calculate min and max lats/lngs
    let lats = locations.map(l => l[0]);
    let lngs = locations.map(l => l[1]);
    let minLat = Math.min.apply(null, lats);
    let maxLat = Math.max.apply(null, lats);
    let minLng = Math.min.apply(null, lngs);
    let maxLng = Math.max.apply(null, lngs);

    var tileset = new SyncTileSet('./data/', [minLat, minLng], [maxLat, maxLng], function(err) {
        if (err) {
            console.log(err);
            return;
        }

        // All tiles are loaded (or downloaded, if they were not already on disk)
        // and queries can be made synchronous.
        locations.forEach(l => {
            console.log(tileset.getElevation([l[0], l[1]]));
        });
    }, {
        username: 'XXX',
        password: 'XXX'
    });