Leafet custom projection

Being a lightweight library, LeafletJS does not support many projections out of the box. But thanks to the proj4leaflet plugin we can use whatever projection we want. In this short tutorial we will create a map using the swiss projection LV95 (EPSG:2056).

The dependencies

var L = require('leaflet')
var proj4 = require('proj4')
var proj4L = require('proj4leaflet')

Define the projection

var lv95 = {
	epsg: 'EPSG:2056',
	def: '+proj=somerc +lat_0=46.95240555555556 +lon_0=7.439583333333333 +k_0=1 +x_0=2600000 +y_0=1200000 +ellps=bessel +towgs84=674.374,15.056,405.346,0,0,0,0 +units=m +no_defs',
	resolutions: [ 4000, 3750, 3500, 3250, 3000, 2750, 2500, 2250, 2000, 1750, 1500, 1250, 1000, 750, 650, 500, 250, 100, 50, 20, 10, 5, 2.5, 2, 1.5, 1, 0.5],
	origin: [2420000, 1350000]
}

Define the CRS

var crs = new L.Proj.CRS(lv95.epsg, lv95.def, { 
	resolutions: lv95.resolutions, 
	origin: lv95.origin
})

Initialize the map

using the CRS and setting max-zoom to the number of available resolutions

var map = L.map('map', { 
	crs: crs,
	maxZoom: lv95.resolutions.length
})

map.setView([47.56,7.59], 22)

We are ready to add some layers.

Add a WMS layer

For this example I used the WMS of Kanton Basel-Stadt.

var wms = L.tileLayer.wms('https://wms.geo.bs.ch/wmsBS?', {
	layers: 'BS.HP.Historische_Stadtplaene.Stadtplan_1946',
	maxZoom: lv95.resolutions.length,
	attribution: '<a href="http://geo.bs.ch">Kanton Basel-Stadt</a>'
}).addTo(map)

Add a GeoJSON layer

For this layer I extracted the churches from the POIs of Kanton Basel.

var geojson = require('./data/churches.json')

To make sure that the data is projected correctly, add define the CRS on the GeoJSON.

geojson.crs = {
	type: 'name',
	properties: { name: 'urn:ogc:def:crs:EPSG::2056' }
}

Add the layer.

L.Proj.geoJson(geojson, {
	pointToLayer: function(feature, latlng) {
		var popup = '<b>' + feature.properties.NAME + '</b><br/>' 
			+ '<small>' + feature.properties.SUBKATEGOR + '</small>' // Define popup 
		return L.marker(latlng).bindPopup(popup) // Represent as marker
  }
}).addTo(map)

That is it.

If you need to convert between swiss coordinates (LV03 and LV95) in the browser or NodeJS, check out swiss-projection-light.