Smart M.App

  Recent months I have been programming  “Green Space Analyzer” web app that shows modern  approach to visualize and  query   multi temporal geospatial data.  User see information in a form he can interact with and discover new patterns, phenomena or information just by very fast ‘feed-back’ of the UI response on the user input.  When user selects for example certain area, all graphs instantly animates transition to reflect selection made, this helps to  better  understand  dynamics of the change. Animation can be seen everywhere – from labels on bar chart, through colors change of the choropleth up to title summary. it creates subtle feeling of control or knowing what has changed and how it has changed. At HxGN 15 conference in   hexagon geospatial keynote, CEO Mladen Stojic showcased it as part of the  vision  called Smart M.App, worth to look at (at 52:40 starts Smart M.App demo):


my Smart M.App  ‘world tour’:





geojson-vt on leaflet

update Sept 2015: nice explanation of how geojson-vt works here

Mapbox technologies used in their webgl and opengl libraries are being extracted into standalone pieces. Vladimir Agafonkin,creator of leaflet.js, earcut.js provided slicing and polygon simplification library for geojson called Goejson-vt.Geojson-vt can slice geosjon into tiles aka mapbox tiles.
Quick test and sample of using geojson-vt on leaflet with canvas drawing available here:

2 videos:

Overview of various geojson samples


folowing video shows 280 MB large geojson !


for comparison here is WebGL version on the same data. This version is loading all data into GPU and leaves everything on WebGL (no optimization). It also takes slightly more time to tessellate all polygons, but once done all seems to run fine. Code used is available here

WMS overlay with MapBox-gl-js 0.5.2

alt textQuick and dirty test of the WMS capabilities of the new MapBox-gl-js 0.5.2 API. First of all, yes ! it is possible to overlay (legacy) WMS over the vector WebGL rendered base map … however the way is not straightforward:


  • Needs some ‘hacks’ as current version of the API doesn’t have enough events to supply custom URL before it is loaded. But check latest version of mapbox, it might have better support for this.
  • Another issue is that WMS server has to provide HTTP header with Access-Control-Allow-Origin:* to avoid WebGL CORS failure when loading image (gl.texImage2D). Usually WMS servers don’t care about this, as for normal img tags CORS doesn’t apply. Here WebGL has access to raw image data so WMS provider has to explicitly agree with this.
  • Build process of mapbox-gl-js tend to be as many other large js projects complicated, slow, complex. And specifically on Windows platform it is more difficult to get mapbox-gl-js install and build running then on Mac.

Code is documented to guide you through the process, few highlights:

 // -- rutine originaly found in GlobalMercator.js, simplified
 // -- calculates spherical mercator coordinates from tile coordinates
 function tileBounds(tx, ty, zoom, tileSize) {
    function pixelsToMeters(px, py, zoom) {
     var res = (2 * Math.PI * 6378137 / 256) / Math.pow(2, zoom),
         originShift = 2 * Math.PI * 6378137 / 2,
         x = px * res - originShift,
         y = py * res - originShift;
     return [Math.abs(x), Math.abs(y)];
   var min = pixelsToMeters(tx * tileSize, ty * tileSize, zoom),
         max = pixelsToMeters((tx + 1) * tileSize, (ty + 1) * tileSize, zoom);
return min.concat(max);


// -- save orig _loadTile function so we can call it later
 // -- there was no good pre-load event at mapbox API to get hooked and patch url
// -- we need to use undocumented _loadTile
 var origFunc = sourceObj._loadTile;
    // -- replace _loadTile with own implementation
 sourceObj._loadTile = function (id) {
    // -- we have to patch sourceObj.url, dirty !
    // -- we basically change url on the fly with correct BBOX coordinates
    // -- and leave rest on original _loadTile processing
     var origUrl =sourceObj.tiles[0]
     var origUrl = origUrl +"&BBOX={mleft},{mbottom},{mright},{mtop}";
     sourceObj.tiles[0] = patchUrl(id, [origUrl]);
     // -- call original method
     return, id);



gist available here

JavaScript – best coding pattern

this or that ? bind or not-bind(this), prototype of prototype ? ehm..all the interesting   things, however better without them in your  code in JavaScript. There is perfect style finally – found in d3, check here: and used in dc.js as well , well described in the d3-cookbok book by Nick Qui Zhu sample code here similar post appeard here “javascript without this” is worth to study the pattern, it will make your code beautiful, modern and readable. You will not need CoffeScript nor TypeScript nor whateverScript.  You even don’t need many other infrastructure or abstractions to get modules or classes  out of JavaScript. It is very elegant.

It is very simple:

function SimpleWidget(spec) {
  var instance = {}; //-- actual instance variable
  var description; // -- private variable

 //-- public API method = function () {
   return instance; //-- returns instance for chaining

 //-- public API method = function (d) {
   //-- getter of private variable
   if (!arguments.length) return description;

    description = d;  //-- setter of private var
    return instance; //-- returns instance for chaining

 return instance; //-- returns instance for chaining
 // usage
var widget = SimpleWidget({color: "#6495ed"})




*** update 1

just came across this great presentation from : and this is exactly the way to think about all of the ‘abstracted stuff’ and syntax sugar or salt that is available today for JavaScript.

“It’s much easier to recover from no abstraction than the wrong abstraction.”

*** update 2

NPM and Browserify  is worth to look at, the way how the complex code is done for example in  MapBox-GL-JS . While I don’t like convoluted modules of modules and source maps with concatenated sources, the syntax and modularization is working well.

Modern data visualization on map

hxgn14 For this year HxGN14  conference  I have prepared a web app  of modern data vizualisation, I have got  inspired by great ideas from Victor Bret and his research and talks for general concept (high interactivity, visualization ) of this app.

It is exciting to see what is possible to do today inside browser and interactivity provided by various open source projects (e.g. leaflet,d3  and its plugins)  and WebGL technology .