title: load csv into leaflet and convert coordinates with proj4
body: <p>This question involves the use of: </p>
  
  <ul>
  <li>leaflet.js (used to create my map) </li>
  <li>leaflet omnivore plugin (used to load my csv data file) </li>
  <li>and proj4 (used to convert easting/northing to lat/lon)</li>
  </ul>
  
  <p>My code below loads a stamen map with leaflet, and then uses omnivore to load my csv file. </p>
  
  <p>In order to display the csv geo data on my map i need to first convert the easting/northing coordinates to lat/lon. The next sections of code contain the logic to do this, and it works successfully for the single coordinate sample within the console.log at the bottom.</p>
  
  <p>But I have no idea how to use this logic on my full csv file. There is one column for easting, one for northing in the file - ultimately i want to my code to convert all these to lat lon, and plot them as points on my map.</p>
  
  <pre><code>var map = L.map('map').setView([51.44, -1.01], 8);
  
  L.tileLayer('https://stamen-tiles-{s}.a.ssl.fastly.net/toner-background/{z}/{x}/{y}.{ext}', 
  {
      subdomains: 'abcd',
      minZoom: 8,
      maxZoom: 20,
      ext: 'png'
  }).addTo(map);
  
  var dataset = omnivore.csv('assets_cwy_new simple.csv');
  
  var osgb = '+proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717 +x_0=400000 +y_0=-100000 +ellps=airy +towgs84=446.448,-125.157,542.06,0.15,0.247,0.842,-20.489 +units=m +no_defs ';
  var wgs84 = '+proj=longlat +datum=WGS84 +no_defs ';
  
  console.log(proj4(osgb,wgs84,[514545.49,215008.4]));
  </code></pre>