jeal (Just Another Elevations Library)

Reads multi-point elevation data from NASA/METI ASTGTM_v003 elevations dataset:

• Obtain elevation values locally and for free


• No request limits or quotas and quicker than API call


• Large number of points can be calculated quickly (250 elevations from a single TIFF < 100ms, will take longer if spread over multiple TIFFs).


• Large coverage at high resolution - each pixel is 1 arc second, being approx 30 resolution at the equator.


• User should be aware of the limitations of the dataset as described in the documentation (links below)


• The compromise is that the TIFF files are large

Dependencies

This library only works with NASA/METI ASTGTM_v003 GeoTiff .dem files downloaded from the appropriate resources (links below). The files should be downloaded as-as and not renamed. Only .dem files are needed, the associated .num files can be deleted.

Useage

Import the library

const jael = require('../src/jael');

Set path to the stored GeoTIFF files:

jael.setPath('./TIFF/');  

Formulate request object, which must be an object with property 'points'. Any other properties will be ignored, and not returned in the results array. Points is an array of lat/long coordinate objects in the form shown below. Note that longitude is designated by 'lng' not 'lon'. Any number of points can be included in the request.

Note that the ASTGTM_v003 dataset only covers up to +/-83degs latitude; providing lats above this will return an error.

The request object is not mutated.

const req = {

  points: [

    {lat: 51.9283, lng: -3.1476},

    {lat: 51.92002, lng: -3.14563}

  ]

};

Make the elevations request. The getElevs() function returns a promise that should be thenned.

jael.getElevs(req).then( ret => {

  console.log(ret);

}).catch( e => {

  console.log(e.message);

});

Points are returned as an array in the requested order with an additional property 'elev' on each point, such as:

[

  { lat: 51.9283, lng: -3.1476, elev: 606 },

  { lat: 51.92002, lng: -3.14563, elev: 571 }

]

Useful links

• https://lpdaac.usgs.gov/products/astgtmv003/


• https://lpdaac.usgs.gov/documents/434/ASTGTM_User_Guide_V3.pdf


• https://search.earthdata.nasa.gov/search?q=C1575726572-LPDAAC_ECS


• http://docs.opengeospatial.org/is/19-008r4/19-008r4.html#_pixelisarea_raster_space


• https://geotiffjs.github.io/geotiff.js/


• http://app.geotiff.io/


• https://www.get-metadata.com/