featureserver

FeatureServer

An open source implementation of the GeoServices specification

Usage

This is meant to be used as a plugin to Express

Example server

const express = require('express')
const app = express() // set up a basic express server
const FeatureServer = require('featureserver')
const cache = require('cache')

// We only need one handler because FeatureServer.route is going to do all the work
const handler = (req, res) => {
  cache.get(/* some geojson */, (err, data) => {
    if (err) res.status(500).json({error: err.message})
    else FeatureServer.route(req, res, data)
  })
}

// Sets up all of the handled routes to support `GET` and `POST`
const routes = ['/FeatureServer', '/FeatureServer/layers', '/FeatureServer/:layer', '/FeatureServer/:layer/:method']

routes.forEach(route => {
  app.route(route)
  .get(handler)
  .post(handler)
})

API

FeatureServer.route

Pass in an incoming request object, an outgoing response object, a geojson object, and options and this function will route and return a geoservices compliant response

• Supports: '/FeatureServer', '/FeatureServer/layers', '/FeatureServer/:layer', '/FeatureServer/:layer/:method'
  • Note: only query, info, and generateRenderer are supported methods at this time.

FeatureServer.route(req, res, data, options)

• data is either a geojson object extended with some additional properties or an object with a layers property which an array of extended geojson objects. These properties are optional and can be used to provide more specific metadata or to shortcut the built in filtering mechanism.

e.g.

{
  type: 'FeatureCollection' // Static
  features: Array, // GeoJSON features
  statistics: Object, // pass statistics to an outStatistics request to or else they will be calculated from geojson features passed in
  metadata: {
    name: String, // The name of the layer
    description: String, // The description of the layer
    extent: Array, // valid extent array e.g. [[180,90],[-180,-90]]
    displayField: String, // The display field to be used by a client
    geometryType: String // REQUIRED if no features are returned with this object Point || MultiPoint || LineString || MultiLineString || Polygon || MultiPolygon
    idField: String, // unique identifier field,
    maxRecordCount: Number, // the maximum number of features a provider can return at once
    limitExceeded: Boolean, // whether or not the server has limited the features returned
    timeInfo: Object // describes the time extent and capabilities of the layer,
    fields: [
     { // Subkeys are optional
       name: String,
       type: String, // 'Date' || 'Double' || 'Integer' || 'String'
       alias: String, // how should clients display this field name,
     }
    ]
  },
  filtersApplied: {
    geometry: Boolean, // true if a geometric filter has already been applied to the data
    where: Boolean, // true if a sql-like where filter has already been applied to the data
    offset: Boolean // true if the result offset has already been applied to the data,
    projection: Boolean // true if the result data has already been projected
  }
  count: Number // pass count if the number of features in a query has been pre-calculated
}

or

{
  layers: [
    {
      type: 'FeatureCollection'
      ...
    },
    {
      type: 'FeatureCollection'
      ...
    }
]

• options is an object that dictates method actions. See FeatureServer.query and FeatureServer.generateRenderer for more details.

FeatureServer.query

Pass in geojson and options (a valid geoservices query object), and the function will perform the query and return a valid geoservices query object. The in addition to input statistics: {}, following is an example of all query options that can be passed into the query route: '/FeatureServer/:layer/query'

e.g.

const options = {
  where: `1=1`,
  objectIds: '1,2,3',
  geometry: {
    xmin: -110, ymin: 30, xmax: -106, ymax: 50,
    spatialReference: { wkid: 4326 },
  },
  geometryType: 'esriGeometryEnvelope',
  spatialRel: 'esriSpatialRelContains',
  outFields: '*',
  returnGeometry: true,
  outSR: 102100, // output spatial reference
  returnIdsOnly: true,
  returnCountOnly: true,
  orderByFields: 'Full/Part_COUNT DESC',
  groupByFieldsForStatistics: 'Full/Part',
  outStatistics: {
  	statisticType: 'count',
  	onStatisticField: '<field>',
  	outStatisticFieldName: 'name'
  },
  returnDistinctValues: true,
  resultOffset: 0,
  resultRecordCount: 0,
  f: 'pjson'
}

FeatureServer.query(geojson, options)

FeatureServer.serverInfo

Generate version 10.21 Geoservices server info

const server = {
  description: String // Describes the collection of layers below,
  maxRecordCount: Number // the maximum number of features a provider can return at once,
  hasStaticData: Boolean // whether or not the server contains any data that is not changing
  layers: [{ // A collection of all the layers managed by the server
    type: 'FeatureCollection',
    metadata: {
      name: String, // The name of the layer
      description: String // The description of the layer
      extent: Array // valid extent array e.g. [[180,90],[-180,-90]]
      displayField: String // The display field to be used by a client
      idField: String // unique identifier field,
      geometryType: String // REQUIRED if no features are returned with this object Point || MultiPoint || LineString || MultiLineString || Polygon || MultiPolygon
      maxRecordCount: Number // the maximum number of features a provider can return at once
      limitExceeded: Boolean, // whether or not the server has limited the features returned
      timeInfo: Object // describes the time extent and capabilities of the layer
    }
    features: [// If all the metadata provided above is provided features are optional.
      {
        type: 'Feature',
        geometry: {
          type: 'Point',
          coordinates: [125.6, 10.1]
        },
        properties: {
          name: 'Dinagat Islands'
        }
      }]
    }
  }]
}

FeatureServer.serverInfo(server)

FeatureServer.layerInfo

Generate version 10.21 Geoservices information about a single layer

FeatureServer.layerInfo(geojson, options)

FeatureServer.layers

Generate version 10.21 Geoservices information about one or many layers

Can pass a single geojson object or an array of geojson objects

FeatureServer.layers(geojson, options)

FeatureServer.generateRenderer

Pass in geojson and options, and the function will return a valid generateRenderer object. Two classificationDef classification types are supported, classBreaksDef and uniqueValueDef.

classBreaksDef is used to classify numeric data based on a number of breaks and a statistical method. Features can also be normalized before being classified. uniqueValueDef is used to classify data based on a unique field(s). If classification breaks are not supplied through in statistics, they will be generated using classificationDef options. The output is a generateRenderer object.

classBreaksDef

In addition to class breaks as input statistics: [], the following is an example of all classBreaksDef options that can be passed into the generateRenderer route: '/FeatureServer/:layer/generateRenderer'

e.g.

const options = {
 *'classificationDef': {
   *'type': 'classBreaksDef',
   *'classificationField': '<field1>',
   *'classificationMethod': 'esriClassifyEqualInterval' | 'esriClassifyNaturalBreaks' | 'esriClassifyQuantile' | 'esriClassifyStandardDeviation',
   *'breakCount': 9,
    'normalizationType': 'esriNormalizeByField' | 'esriNormalizeByLog' | 'esriNormalizeByPercentOfTotal',
    'normalizationField': '<field2>' // mandatory if 'normalizationType' === 'esriNormalizeByField'
    'baseSymbol': {
      'type': 'esriSMS',
      'style': 'esriSMSCircle',
      'width': 2
    },
    'colorRamp': {
      'type': 'algorithmic',
      'fromColor': [115,76,0,255],
      'toColor': [255,25,86,255],
      'algorithm': 'esriHSVAlgorithm'
    }
  },
  'where': '<field2> > 39'
}

FeatureServer.generateRender(geojson, options)

*required

Output:

{
  type: 'classBreaks',
  field: '<field1>',
  classificationMethod: 'esriClassifyEqualInterval',
  minValue: 0,
  classBreakInfos: [
    {
      classMinValue: 0,
      classMaxValue: 5,
      label: '0-5',
      description: '',
      symbol: {
        type: 'esriSMS',
        style: 'esriSMSCircle',
        width: 2,
        color: [115, 76, 0]
      }
    },
    {
      classMinValue: 6,
      classMaxValue: 11,
      label: '6-11',
      description: '',
      symbol: {
        type: 'esriSMS',
        style: 'esriSMSCircle',
        width: 2,
        color: [156, 67, 0]
      }
    },
    ...
  ]
}

uniqueValueDef

The following is an example of all uniqueValueDef options that can be passed into the generateRenderer route: '/FeatureServer/:layer/generateRenderer'

e.g.

const options = {
 *'classificationDef': {
   *'type': 'uniqueValueDef',
   *'uniqueValueFields': ['Genus', '<field2>', '<field3>'],
   *'fieldDelimiter': ', '
    'baseSymbol': {
      'type': 'esriSMS',
      'style': 'esriSMSCircle',
      'width': 2
    },
    'colorRamp': {
      'type': 'algorithmic',
      'fromColor': [115,76,0,255],
      'toColor': [255,25,86,255],
      'algorithm': 'esriHSVAlgorithm'
    }
  },
  'where': 'latitude > 39'
}

FeatureServer.generateRender(geojson, options)

*required

Output:

{
  type: 'uniqueValue',
  field1: 'Genus',
  field2: '',
  field3: '',
  fieldDelimiter: ', ',
  defaultSymbol: {},
  defaultLabel: '',
  uniqueValueInfos: [
    {
      value: 'MAGNOLIA',
      count: 5908,
      label: 'MAGNOLIA',
      description: '',
      symbol: {
        type: 'esriSMS',
        style: 'esriSMSCircle',
        width: 2,
        color: [115, 76, 0]
  	   }
    },
    {
      value: 'QUERCUS',
      count: 12105,
      label: 'QUERCUS',
      description: '',
      symbol: {
        type: 'esriSMS',
        style: 'esriSMSCircle',
        width: 2,
        color: [116, 76, 0]
  	  }
   },
   ...
  ]