Leaflet schematic

This is a set of tools to display and work with non-cartographic large high-detailed SVG schematics or blueprints. SVG is a perfect format for the task - it's vector, relatively compact, has all the means to work with templates and symbols, so it can really be a great representation and metadata container at the same time.

Usage

var xhr = require('xhr');
var SVGOverlay = require('leaflet-schematic');
 
var map = L.map('map', { crs: L.CRS.Simple });
L.svgOverlay('/path/to/svg.svg', {
  load: function(url, callback) {
    // your/your library xhr implementation
    xhr({
      uri: url,
      headers: {
        "Content-Type": "image/svg+xml"
      }
    }, function (err, resp, svg) {
      callback(err, svg);
    });
  }
}).addTo(map);

Problem

The problem is that if you want to work with the SVG as with image overlay, several technical limitations and performance issues strike in:

• you cannot work on larger scales with the whole canvas because of the dimension restrictions of browsers
• you have to scale the drawing initially to fit the viewport on the certain zoom level
• IE (as always) - I wouldn't even call that "SVG support"
  • <use> elements have a special freaky non-compliant API which is also broken
  • css-transforms - unsupported
  • translate() + scale() transform on <g> -doesn't work, use matrix
  • horrible performance - the more SVG nodes you have the slower it is

Approach

• Use leaflet viewportized layer container to render part of the SVG with padding
• scale SVG to fit the viewport and zoom levels
• pack SVG contents into moving <g>
• for IE - hardcore hacking:
  • render SVG > base64 > <canvas>
  • replace SVG with this canvas on drag and zoom
  • also keep a hidden PNG rendered to overcome IE's performance drop on image scaling, somehow it works like a directive to switch the faulty smoothing off

Know issues

• SVGs without correctly provided viewBox work really badly and I cannot yet figure out why. I'm trying to calculate viewbox from the contents, but it still looks broken in rendered canvas

License

MIT