Creating a node.js GeometryService : part 2

This is my second post on what I learned from creating an implementation of the geometryservice specification in node.js. The first post can be found here.

By default node.js doesn't reload your files when they have changed but while developing this can be very handy. The most easy to use tool for node.js on windows that monitors your files for changes, with an easy way to set the node.js debugging flag, is nodemonw. You can download nodemonw at Once you've downloaded the executable I suggest to copy it to your %Appdata%\npm directory or another directory thats in your path. To start nodemonw I now run the following command nodemonw --debug index.js. In the next section it will become clear why I added the --debug flag.

To be able to debug my node.js application I installed node-inspector (npm install -g node-inspector). As you can read in the readme of node-inspector it is really easy to get started with node-inspector. You just have to start node-inspector and then open in your favorite WebKit based browser. On Wikipedia I found this list of WebKit based browsers. The most well known ones for Windows are Google Chrome and Safari. A screencast on node-inspector can be found here. There is also a node-inspector playlist on YouTube.

To be able to test parts of my GeometryService I used vows (npm install -g vows). Vows is an asynchronous behavior driven development framework. More info about it can be found on I am now going to show a small part of the code from my GeometryService and some tests I wrote for this code. My directory structure for the code I'll show looks like this: lib/
-- datatransformer.js
-- datatransformers.test.js
In datatransformer.js I started a function to convert an ESRI geometry JSON object to wkt based on its geometry type.

exports.esriGeoJsonToWKT = function esriGeoJsonToWKT (geometryType, geometry) {
  if(geometryType === "esriGeometryPoint") {
    return "POINT(" + geometry.x + " " + geometry.y + ")";

And the content of datatransformer.test.js is:

var dt = require("../lib/datatransformer");
var vows = require('vows');
var assert = require('assert');

vows.describe('Esri geometry JSON to WKT').addBatch({
  'when converting esriGeometryPoint {"x":-117,"y":34}':{
    topic: function(){ 
      var geomType = 'esriGeometryPoint';
      var p = JSON.parse('{"x":-117,"y":34}');
      return dt.esriGeoJsonToWKT(geomType, p);
    'we get "POINT(-117 34)"': function(topic){
      assert.equal(topic, "POINT(-117 34)");
  'but when converting esriGeometryPoint {"x":-117.01,"y":34.02}':{
    topic: function(){ 
      var geomType = 'esriGeometryPoint';
      var p = JSON.parse('{"x":-117.01,"y":34.02}');
      return dt.esriGeoJsonToWKT(geomType, p);
    'we get "POINT(-117.01 34.02)"': function(topic){
      assert.equal(topic, "POINT(-117.01 34.02)");

As you can see I created two tests for converting point geometries from ESRI JSON to wkt. One for integer coordinates and one for decimal coordinates. The easiest way to run this tests with vows on windows was opening a commandline in the root directory of my node.js project and type vows --spec. This will run the tests it finds in the test and spec directories of your project. My output looks like this :

? Esri geometry JSON to WKT

when converting esriGeometryPoint {"x":-117,"y":34}
V we get "POINT(-117 "4)"
but when converting esriGeometryPoint {"x":-117.01,"y":34.02}
V we get "POINT(-117.01 34.02)"

V OK » 2 honored (0.007s)

On a side note if you ever encounter that node can't find any of your globally installed packages then it might help to add a new User Variable called NODE_PATH with as value %AppData%\npm\node_modules. That was it for this post more posts on this project will follow.

As I announced in this post, I open sourced the code of this project. It can be found in this bitbucket repository.


qvvo said...

Great,waiting for the "part 3"

Rogger Backs said...

Awesome! Great work with this post, i am sure people should have got impressed with this post.