torque.js internals

(no more tweets maps from here)

a little bit of history

options to show animated datasets

a set of tiles per month

vector information

vector, what could go wrong ?

common pattern

torque.js is a library that allows to render points on top of google maps or leaflet...

animated

and using CartoCSS

  #layer {
    marker-fill: #FEO;
    line-color: #FABADA;
  }
  

example: 1M points dataset

tech

• data format: tilecubes
• server side tile generation
• client side renderer

data format

quantification and aggreation
coordinates and time

  [
    {
      // webmercator snapped to tile pixel
      x__uint8: 8,
      y__uint8: 10,

      // steps * floor((date - min_date)/(max_date - min_date) )
      date__uint16: [0, 10, 45, 46],

      // values for steps aggregated
      vals__uint8:  [1, 3 , 5 , 10]
    },
    ...
  ]

  [
    {
      // webmercator snapped to tile pixel
      x__uint8: 8,
      y__uint8: 10,

      // steps * floor((date - min_date)/(max_date - min_date) )
      date__uint16: [0, 10, 45, 46],

      // values for steps aggregated
      vals__uint8:  [1, 3 , 5 , 10]
    },
    ...
  ]

  [
    {
      // webmercator snapped to tile pixel
      x__uint8: 8,
      y__uint8: 10,

      // steps * floor((date - min_date)/(max_date - min_date) )
      date__uint16: [0, 10, 45, 46],

      // values for steps aggregated
      vals__uint8:  [1, 3 , 5 , 10]
    },
    ...
  ]

  [
    {
      // webmercator snapped to tile pixel
      x__uint8: 8,
      y__uint8: 10,

      // steps * floor((date - min_date)/(max_date - min_date) )
      date__uint16: [0, 10, 45, 46],

      // values for steps aggregated
      vals__uint8:  [1, 3 , 5 , 10]
    },
    ...
  ]

server side

nodejs + postgres

 WITH
      par AS (
        SELECT ({xyz_resolution})*{resolution} as res
      , 1.0/(({xyz_resolution})*{resolution}) as resinv
      , ST_MakeEnvelope({xmin}, {ymin}, {xmax}, {ymax}, {srid}) as ext )
      SELECT xx x__uint8,
             yy y__uint8,
             array_agg(c) vals__uint8,
             array_agg(d) dates__uint16
       FROM (
       select
           GREATEST(0, LEAST(255, round((st_x(i.{gcol}) - st_xmin(p.ext))*resinv))) as xx,
           GREATEST(0, LEAST(255, round((st_y(i.{gcol}) - st_ymin(p.ext))*resinv))) as yy
           , {countby} c
           , floor(({column_conv} - {start})/{step}) d
            FROM ({_sql}) i, par p
            WHERE i.{gcol} && p.ext  GROUP BY xx, yy, d
        ) cte, par
      GROUP BY x__uint8, y__uint8;

client side

• transform tile format to render format
• cartocss2js compiler
• renderer

tile processing

tile -> TypedArrays

  pixels: [x, y, x, y, x, y...]
  values: [pixelIndex, value, pixelIndex, value, ....]
  time_slots:  [valueIndex, valueCount, valueIndex, valueCount]
  

  pixels: [x, y, x, y, x, y...]
  values: [pixelIndex, value, pixelIndex, value, ....]
  time_slots:  [valueIndex, valueCount, valueIndex, valueCount]
  

  pixels: [x, y, x, y, x, y...]
  values: [pixelIndex, value, pixelIndex, value, ....]
  time_slots:  [valueIndex, valueCount, valueIndex, valueCount]
  

  pixels: [x, y, x, y, x, y...]
  values: [pixelIndex, value, pixelIndex, value, ....]
  time_slots:  [valueIndex, valueCount, valueIndex, valueCount]
  

    [
      {
        x__uint8: 8,
        y__uint8: 10,
        date__uint16: [0, 10, 45, 46],
        vals__uint8:  [1, 3 , 5 , 10]
      },
      ...
    ]
  

    [
      {
        x__uint8: 8,
        y__uint8: 10,
        date__uint16: [0, 10, 45, 46],
        vals__uint8:  [1, 3 , 5 , 10]
      },
      ...
    ]
  

styling - cartocss2js

javascript shaders

  {
    'marker-width': function(ctx, value) {
      return value * 0.1 * ctx.zoom;
    },
    'line-color': function(ctx, value) {
      return ctx.zoom > 10 ? '#FFF': '#000';
    }
  }
  

  #layer {
    marker-width: 10;
    /* shows the previous time frame */
    [frame-offset = 1] {
      marker-width: 5;
    }
  }
  

data, style and rendering

canvas 2D

full canvas
vs
tile canvas

  for point in points_in_slot(time) {
    style = evaluateShader(point.value)
    renderPoint(point.coords, style)
  }
  

but sometimes the style is heavy

dynamic sprites everywhere

future

webgl

thanks
@javisantana