streaming geo-statistics about GeoJSON
A way to calculate geographic statistics about a set of GeoJSON features. This module presents you with a transparent pass-through stream that calculates statistics as you pass objects into it. This allows the module to fit in a processing or transformation pipeline and calculate statistics without getting in the way.
var geoStatistics = require'stream-geo-statistics';var geojsonStream = require'geojson-stream';var myPipeline = require'./the-rest-of-my-pipeline';var fs = require'fs';fscreateReadStream'my-feature-collection.geojson'pipegeojsonStreamparse // Processes file as discrete featurespipegeoStatistics // Collects statistics and passes features throughpipemyPipeline; // Receives features and does whatever to themmyPipelineon'finish'var stats = geoStatisticsgetStats;;
You must stream in discrete GeoJSON features, not a stringified representation of a FeatureCollection. geojson-stream can help.
.getStats()will return an object with the following keys:
bbox: as and array of
[ east, south, west, north ]for all features
density: as statistics on the distance between coordinates for all features
duplicates: as statistics on the number of duplicate coordinates per feature
coordinates: as statistics on the number of coordinates per feature
features: the number of features that have come through
tiles: spherical-mercator tiles as an array of
[ "z/x/y" ]covering all features
Each "statistics" object (e.g.
coordinates) is data collected from a stream-statistics object that presents min, max, sum, mean, mode, variance, standard_deviation, geometric_mean and harmonic_mean.
Calculating tile lists is currently the most expensive operation by far. So, if you do not specifically ask for it, tile lists are not generated. In order to generate tile lists, you must pass an
options object when creating your statistics stream. For example:
var geoStatistics = require'stream-geo-statistics';var myStream = geoStatisticsmaxZoom: 14 // must be provided in order to generate tile liststileSize: 512 // optional, defaults to 256;