Adds the simplification mode documentation

README.md

@@ -1,7 +1,10 @@
 # Vector Tile optimizer
 
 [![Build Status Linux](https://travis-ci.org/ibesora/vt-optimizer.svg?branch=master)](https://travis-ci.org/ibesora/vt-optimizer)
-> A small NodeJS cli tool to inspect and optimize [Mapbox Vector Tiles](https://www.mapbox.com/vector-tiles/) files
+[![Build status](https://ci.appveyor.com/api/projects/status/7c6haos5thbxrnu4/branch/master?svg=true)](https://ci.appveyor.com/project/ibesora/vt-optimizer/branch/master)
+![Dependency Status](https://david-dm.org/ibesora/vt-optimizer.svg)
+![License](https://img.shields.io/badge/license-MIT-blue.svg)
+> A small NodeJS cli tool to inspect and optimize [Mapbox MBTiles files](https://github.com/mapbox/mbtiles-spec) used to encode [Mapbox Vector Tiles](https://www.mapbox.com/vector-tiles/).
 
 <img src="media/example.gif">
 
@@ -49,4 +52,9 @@ It reads both the Vector Tile and style and removes all the layers and features
 **Note:** To use the optimization tool it's better to run the `--max-old-space-size` NodeJS argument to increase NodeJS process heap space as the entire Vector Tile is loaded and decompressed when working.
 ```
 node --max-old-space-size=16386 index.js -m files/input.mbtiles -s files/style.json -o files/output.mbtiles
-```
+```
+### Vector Tile layer simplification
+When running the tool with the *-x X -y Y -z Z -l layerName -t tolerance* arguments, the simplification mode will be started. This mode is used for simplifying a layer on a given tile. **Note:** The tolerance value is in degrees (1º is aproximately 110 meters) and tells the algorithm that two points with a distance lower than the tolerance value should be merged.
+
+When the process is finished, the results of the simplification are shown.
+<img src="media/simplify.PNG">

src/core/VTProcessor.js

@@ -420,11 +420,11 @@ class VTProcessor {
 
 						}
 
-						ctx.startingCoordinatesNum = layerToSimplify.features.reduce((accum, elem) => accum + elem.geometry.coordinates.length, 0);
+						ctx.startingCoordinatesNum = layerToSimplify.features.reduce((accum, feature) => accum + feature.geometry.coordinates.reduce((accum, ring) => (ring.length ? accum + ring.length : feature.geometry.coordinates.length / 2), 0), 0);
 						Simplifier.simplifyGeoJSON(layerToSimplify, tolerance)
 							.then(data => {
 
-								ctx.simplifiedCoordinatesNum = data.features.reduce((accum, elem) => accum + elem.geometry.coordinates.length, 0);
+								ctx.simplifiedCoordinatesNum = data.features.reduce((accum, feature) => accum + feature.geometry.coordinates.reduce((accum, ring) => (ring.length ? accum + ring.length : feature.geometry.coordinates.length / 2), 0), 0);
 								ctx.geojsons[layerName] = data;
 								resolve();