Merge pull request #47 from conveyal/dev

Add additional code to produce spectrograms

lib/get-spectrogram-data.js

@@ -0,0 +1,50 @@
+/** Get data to render a spectrogram plot from browsochrones data */
+
+import propagate from './propagation'
+
+const MAX_TRIP_LENGTH = 120 // minutes
+
+/**
+ * Return data used to draw a spectrogram.
+ * This is basically just an array of curves like so:
+ * For each iteration you will have an array of
+ *  [opportunities reachable in 1 minute,
+ *   marginal opportunities reachable in 2 minutes,
+ *   ...
+ *   marginal opportunities reachable in 120 minutes]
+ */
+export default function getSpectrogramData ({origin, query, stopTreeCache, grid}) {
+  const output = []
+  for (let i = 0; i < origin.nMinutes; i++) output.push(new Uint32Array(MAX_TRIP_LENGTH))
+
+  propagate({
+    query,
+    stopTreeCache,
+    origin,
+    callback: ({
+      travelTimesForDest,
+      x,
+      y
+    }) => {
+      let gridx = x + query.west - grid.west
+      let gridy = y + query.north - grid.north
+
+      // off the grid, return
+      if (gridx < 0 || gridy < 0 || gridx >= grid.width || gridy >= grid.height) return
+
+      const val = grid.data[gridy * grid.width + gridx]
+
+      for (let i = 0; i < travelTimesForDest.length; i++) {
+        const time = travelTimesForDest[i]
+        if (time === 255) continue // unreachable
+
+        if (time < MAX_TRIP_LENGTH) {
+          // time - 1 so areas reachable in 1 minute will be included in output[i][0]
+          // TODO audit all the places we're flooring things
+          output[i][time - 1] += val
+        }
+      }
+    }})
+
+  return output
+}

lib/get-surface.js

@@ -1,9 +1,7 @@
-import fill from 'lodash.fill'
 import dbg from 'debug'
+import propagate from './propagation'
 const debug = dbg('browsochrones:get-surface')
 
-import {getNonTransitTime, ITERATION_WIDTH} from './origin'
-
 /**
  * Get a travel time surface and accessibility results for a particular origin.
  * Pass in references to the query (the JS object stored in query.json), the stopTreeCache, the origin file, the
@@ -21,63 +19,27 @@ export default function getSurface ({origin, query, stopTreeCache, which}) {
 
   // how many departure minutes are there. skip number of stops
   const nMinutes = origin.data[transitOffset + 1]
-  const travelTimesForDest = new Uint8Array(nMinutes) // the total travel time per iteration to reach a particular destination
-  const waitTimesForDest = new Uint8Array(nMinutes) // wait time per iteration for particular destination
-  const inVehicleTravelTimesForDest = new Uint8Array(nMinutes) // in-vehicle travel time per destination
-  const walkTimesForDest = new Uint8Array(nMinutes)
-
-  // x and y refer to pixel not origins here
-  // loop over rows first
-  for (let y = 0, pixelIdx = 0, stcOffset = 0; y < query.height; y++) {
-    for (let x = 0; x < query.width; x++, pixelIdx++) {
-      const nStops = stopTreeCache.data[stcOffset++]
-
-      // can we reach this pixel without riding transit?
-      const nonTransitTime = getNonTransitTime(origin, {x, y})
-
-      // fill with unreachable, or the walk distance
-      fill(travelTimesForDest, nonTransitTime)
-      fill(waitTimesForDest, 255)
-      fill(inVehicleTravelTimesForDest, 255)
-      fill(walkTimesForDest, nonTransitTime) // when the origin is within walking distance and
-        // walking is the fastest way to reach the destination, _everything_ is walk time
-
-      for (let stopIdx = 0; stopIdx < nStops; stopIdx++) {
-        // read the stop ID
-        const stopId = stopTreeCache.data[stcOffset++]
-
-        // read the time (minutes)
-        const time = stopTreeCache.data[stcOffset++]
-
-        for (let minute = 0; minute < nMinutes; minute++) {
-          const offset = origin.index[stopId] + minute * ITERATION_WIDTH
-          const travelTimeToStop = origin.data[offset]
-
-          if (travelTimeToStop !== -1) {
-            const travelTimeToPixel = travelTimeToStop + time
-
-            // no need to check that travelTimeToPixel < 255 as travelTimesForDest[minute] is preinitialized to the nontransit time or 255
-            if (travelTimesForDest[minute] > travelTimeToPixel) {
-              travelTimesForDest[minute] = travelTimeToPixel
-              let inVehicle = inVehicleTravelTimesForDest[minute] = origin.data[offset + 1]
-              let wait = waitTimesForDest[minute] = origin.data[offset + 2]
-              // NB when we're talking about a particular trip, then walk + wait + inVehicle == total
-              // However if you calculate summary statistics for each of these individually, that may
-              // not be true. So we need to calculate walk here and explicitly calculate summary stats about it.
-              let walkTime = travelTimeToPixel - wait - inVehicle
-              walkTimesForDest[minute] = walkTime
-            }
-          }
-        }
-      }
 
+  propagate({
+    query,
+    stopTreeCache,
+    origin,
+    callback: ({
+      travelTimesForDest,
+      walkTimesForDest,
+      inVehicleTravelTimesForDest,
+      waitTimesForDest,
+      x,
+      y
+    }) => {
+      const pixelIdx = y * query.width + x
       // compute and set value for pixel
       surface[pixelIdx] = computePixelValue(which, travelTimesForDest)
       waitTimes[pixelIdx] = computePixelValue(which, waitTimesForDest)
       walkTimes[pixelIdx] = computePixelValue(which, walkTimesForDest)
       inVehicleTravelTimes[pixelIdx] = computePixelValue(which, inVehicleTravelTimesForDest)
     }
-  }
+  })
 
   debug('generating surface complete')
 

lib/grid.js

@@ -6,8 +6,13 @@ export function create (data) {
   const array = new Int32Array(data, 4 * 5)
   const header = new Int32Array(data)
 
+  let min = Infinity
+  let max = -Infinity
+
   for (let i = 0, prev = 0; i < array.length; i++) {
     array[i] = (prev += array[i])
+    if (prev < min) min = prev
+    if (prev > max) max = prev
   }
     // parse header
   return {
@@ -16,6 +21,8 @@ export function create (data) {
     north: header[2],
     width: header[3],
     height: header[4],
-    data: array
+    data: array,
+    min,
+    max
   }
 }

lib/index.js

@@ -1,5 +1,6 @@
 import WebWorkerPromiseInterface from 'web-worker-promise-interface'
 import {Map as LeafletMap} from 'leaflet' // NB raw leaflet map not react-leaflet
+import {create as createGridFunc} from './grid'
 
 import workerHandlers from './worker-handlers'
 
@@ -73,6 +74,19 @@ export default class Browsochrones extends WebWorkerPromiseInterface {
     })
   }
 
+  getSpectrogramData (grid) {
+    if (!this.isLoaded()) {
+      return Promise.reject(new Error('Accessibility cannot be computed before generating a surface.'))
+    }
+
+    return this.work({
+      command: 'getSpectrogramData',
+      message: {
+        grid
+      }
+    })
+  }
+
   generateDestinationData (point) {
     return this.work({
       command: 'generateDestinationData',
@@ -255,12 +269,15 @@ export default class Browsochrones extends WebWorkerPromiseInterface {
   }
 
   /** Get a GeoJSON isochrone with the given cutoff (in minutes) */
-  getIsochrone (cutoff = 60) {
+  getIsochrone (cutoff = 60, interpolation = true) {
     return this.work({
       command: 'getIsochrone',
       message: {
-        cutoff
+        cutoff,
+        interpolation
       }
     })
   }
 }
+
+export const createGrid = createGridFunc

lib/propagation.js

@@ -0,0 +1,81 @@
+/**
+ * Perform propagation from an origin to destination cells, calling a callback to summarize the data.
+ *
+ * This seems like it's overly complicated, but I don't think there's an easier way to have this code
+ * used both to create surfaces/isochrones and spectrogram data, which are different summaries of the data.
+ *
+ * The callback will be called with the following, once for each destination pixel
+ *   travelTimesForDest: Travel times at each iteration
+ *   walkTimesForDest: Walk times at each iteration
+ *   inVehicleTravelTimesForDest: In vehicle travel times at each iteration
+ *   waitTimesForDest: Wait times at each iteration
+ *   x: X coordinate of grid for this destination
+ *   y: Y coordinate of grid for this destination
+ */
+
+import fill from 'lodash.fill'
+import {getNonTransitTime, ITERATION_WIDTH} from './origin'
+
+export default function propagate ({ query, stopTreeCache, origin, callback }) {
+  let {nMinutes} = origin
+  const travelTimesForDest = new Uint8Array(nMinutes) // the total travel time per iteration to reach a particular destination
+  const waitTimesForDest = new Uint8Array(nMinutes) // wait time per iteration for particular destination
+  const inVehicleTravelTimesForDest = new Uint8Array(nMinutes) // in-vehicle travel time per destination
+  const walkTimesForDest = new Uint8Array(nMinutes)
+
+  // x and y refer to pixel not origins here
+  // loop over rows first
+  for (let y = 0, pixelIdx = 0, stcOffset = 0; y < query.height; y++) {
+    for (let x = 0; x < query.width; x++, pixelIdx++) {
+      const nStops = stopTreeCache.data[stcOffset++]
+
+      // can we reach this pixel without riding transit?
+      const nonTransitTime = getNonTransitTime(origin, {x, y})
+
+      // fill with unreachable, or the walk distance
+      fill(travelTimesForDest, nonTransitTime)
+      fill(waitTimesForDest, 255)
+      fill(inVehicleTravelTimesForDest, 255)
+      fill(walkTimesForDest, nonTransitTime) // when the origin is within walking distance and
+        // walking is the fastest way to reach the destination, _everything_ is walk time
+
+      for (let stopIdx = 0; stopIdx < nStops; stopIdx++) {
+        // read the stop ID
+        const stopId = stopTreeCache.data[stcOffset++]
+
+        // read the time (minutes)
+        const time = stopTreeCache.data[stcOffset++]
+
+        for (let minute = 0; minute < nMinutes; minute++) {
+          const offset = origin.index[stopId] + minute * ITERATION_WIDTH
+          const travelTimeToStop = origin.data[offset]
+
+          if (travelTimeToStop !== -1) {
+            const travelTimeToPixel = travelTimeToStop + time
+
+            // no need to check that travelTimeToPixel < 255 as travelTimesForDest[minute] is preinitialized to the nontransit time or 255
+            if (travelTimesForDest[minute] > travelTimeToPixel) {
+              travelTimesForDest[minute] = travelTimeToPixel
+              const inVehicle = inVehicleTravelTimesForDest[minute] = origin.data[offset + 1]
+              const wait = waitTimesForDest[minute] = origin.data[offset + 2]
+              // NB when we're talking about a particular trip, then walk + wait + inVehicle == total
+              // However if you calculate summary statistics for each of these individually, that may
+              // not be true. So we need to calculate walk here and explicitly calculate summary stats about it.
+              const walkTime = travelTimeToPixel - wait - inVehicle
+              walkTimesForDest[minute] = walkTime
+            }
+          }
+        }
+      }
+
+      callback({
+        travelTimesForDest,
+        walkTimesForDest,
+        inVehicleTravelTimesForDest,
+        waitTimesForDest,
+        x,
+        y
+      })
+    }
+  }
+}

lib/worker-handlers.js

@@ -9,6 +9,7 @@ import {create as createGrid} from './grid'
 import * as mercator from './mercator'
 import {create as createOrigin} from './origin'
 import {create as createStopTreeCache} from './stop-tree-cache'
+import getSpectrogramData from './get-spectrogram-data'
 
 module.exports = createHandler({
   putGrid (ctx, message) {
@@ -108,6 +109,7 @@ module.exports = createHandler({
       width: ctx.query.width,
       height: ctx.query.height,
       cutoff: message.cutoff,
+      interpolation: message.interpolation,
       // coords are at zoom level of query
       project: ([x, y]) => {
         return [mercator.pixelToLon(x + ctx.query.west, ctx.query.zoom), mercator.pixelToLat(y + ctx.query.north, ctx.query.zoom)]
@@ -127,5 +129,13 @@ module.exports = createHandler({
       stopTreeCache: ctx.stopTreeCache,
       to: message.point
     })
+  },
+  getSpectrogramData (ctx, message) {
+    return getSpectrogramData({
+      origin: ctx.origin,
+      query: ctx.query,
+      stopTreeCache: ctx.stopTreeCache,
+      grid: ctx.grids.get(message.grid)
+    })
   }
 })

package.json

@@ -35,9 +35,9 @@
     "normalize.css": "^5.0.0",
     "react": "^15.3.1",
     "react-dom": "^15.3.1",
+    "semantic-release": "^4.3.5",
     "tape": "^4.2.2",
-    "transitive-js": "^0.8.2",
-    "semantic-release": "^4.3.5"
+    "transitive-js": "^0.8.2"
   },
   "standard": {
     "parser": "babel-eslint"