dline

JavaScript library for interpolating and generating contours

Istallation

use npm to install dline in node.js

 npm i dline

or CDN to include dline in browser

 <script src="https://unpkg.com/[email protected]/dist/dline.min.js"></script>

Documentation

Converters

Helper methods for converting formats

ascToArray and pointGridToArray

Converting string Esri ASCII grid or GeoJSON pointgird to dline array {grid,latCellSize,longCellSize,bbox,noData}

 dline.ascToArray(asc)

 dline.pointGridToArray(geoJson,z)

z - the property name, default 'value'

pointsToArray

Converting GeoJSON points to [[lat1,long1,z1],[lat2,long2,z2]...]

 dline.pointsToArray(geoJson,z)

z - the property name, default 'value'

Interpolation

dline uses the IDW method as interpolation. There is also an experimental function of using a mask to calculate a unique weight in each cell of the output grid

 dline.IDW(points, cellSize, options);

Arguments

• points - reference point array [[lat1,long1,z1],[lat2,long2,z2]...]
• cellSize - [latCellSize,longCellSize] only for degrees or value for degrees or meters units
• options - additional optional settings

Options

• bbox - default [0,0], can be an ordinary bbox like [minLong, minLat, maxLong, maxLat] or [longPercent, latPercent], in this case increases the size of the grid by longPercent,latPercent from extreme points
• units - default ["meters","meters"], can be [cellSizeUnits,distanceUnits], where cellSizeUnits - output grid cell size, distanceUnits - units of distance in IDW method. If you set only "degrees" it equal ["degrees","degrees"], with meters as well
• exponent - default 2, exponent of distance in IDW method
• mask - the grid to adjust the weight of each point in each cell, {grid,latCellSize,longCellSize,bbox,noData}, converting from GeoJSON or Esri ASCII, see converters
• boundaries - using only with mask, array of reference values which increases or decreases weight by some x value if the mask cell differs from the cell lying on the path to the desired value, [[value1,x1],[value2,x2]...]

Example

const  points = [
	[55.98, 92.76, 4],
	[56.02, 92.76, 7],
	[56.09, 92.74, 2],
	[56.02, 92.79, 18],
	[55.97, 92.67, 4]
];
const  mask = dline.ascToArray(await  fetch('./some_asc_file.asc').then(res  =>  res.text()));
const  grid = dline.IDW(points, 100, { bbox: [10, 10], exponent:  3, units: ['meters', 'degrees'], mask, boundaries: [[20, 0.2], [-50, 0.1]] });

Isolines and Isobands

Uses Marching squares algorithm for generating contours. Return GeoJSON.

 dline.isolines(grid,breaks)

 dline.isobands(grid,breaks)

Arguments

• grid - grid that the dline.IDW method returns. If you whant to use GeoJSON pointgrid or Esri ASCII, see converters
• breaks - array of contour values, [v1,v2,v3...]

Example

const  points = // some random points
const  bands = dline.isobands(dline.IDW(points,500),[1,2,3,4,5])