How do I create a minimap of an SVG using D3 v5 and show the current viewport dimensions?

user_1199594 0
Viewed 2340

I am importing an external SVG using the code below and I have attached zoom and pan behavior to it, which is working fine.

I have also created a type of minimap, which shows the same SVG, but only as a smaller version.

I would like to show a rectangle on the minimap that represents the current viewport shown on the screen. However, I am having trouble with the correct scaling and positioning.

JS CODE:

let url = 'https://gist.githubusercontent.com/ivanbacher/11cd328411c74b2bc2ec789291852544/raw/bb39be70f71e4fb52ae5101150f5fffde4b66272/map.svg';


d3.svg(url).then( (xml)=> {

   let width = parseInt( d3.select('body').style('width') );
   let height = parseInt( d3.select('body').style('height') );

   document.querySelector('#map').appendChild(xml.documentElement.cloneNode(true));
   document.querySelector('#minimap').appendChild(xml.documentElement.cloneNode(true));


   let map = d3.select('#map').select('svg')
   let minimap = d3.select('#minimap').select('svg')
                    .attr('width', 200);

   let transform = d3.zoomIdentity.translate(0, 0).scale(1);

   let zoom = d3.zoom()
      .scaleExtent([1, 3])
      .on('zoom', zoomed);

   map.call(zoom)
      .call(zoom.transform, transform);

   function zoomed() {
      let mapMainContainer = map.select('#main_container')
         .attr('transform', d3.event.transform);

      minimap.select('#minimapRect').remove();

      let mapWidth = parseFloat( d3.select('#map').style('width') );
      let mapHeight = parseFloat( d3.select('#map').style('height') );


      let minimapWidth = parseFloat( d3.select('#minimap').style('width') );
      let minimapHeight = parseFloat( d3.select('#minimap').style('height') );

      let minimapScale = minimapWidth / mapWidth ;   // size of big map times this = size of minimap
      let minimapRect = minimap.append('rect')
          .attr('id', 'minimapRect')
          .attr('width', minimapWidth / minimapScale) //HERE?
          .attr('height', minimapHeight / minimapScale ) //HERE?
          .attr('stroke', 'red')
          .attr('fill', 'black')
          .attr('transform', `translate(${-d3.event.transform.x},${-d3.event.transform.y}) scale(${d3.event.transform.k})`);
   }
})

Here is a working version of the code + pan and zoom behaviours.

enter image description here

UPDATE

Working codepen version

d3.js svg javascript
2 Answers

You are currently constraining the size of the main map to 600px via the enclosing div element, and the mini map to 200px. Note that the coordinate system that both are using will be the same, though. Your calculations need to take into account the difference between the size of the SVG viewBox and the main map size, i.e.

let mapWidth = parseFloat( d3.select('#map').style('width') );
let mapHeight = parseFloat( d3.select('#map').style('height') );
let factor = mapWidth / d3.select('#map svg').attr('viewBox').split(' ')[2]

The dimensions of the rect on the mini map should be set using this scaling factor:

  let minimapRect = minimap.append('rect')
      .attr('id', 'minimapRect')
      .attr('width', mapWidth / factor )
      .attr('height', mapHeight / factor )

When the zoom events occur, you already have the x and y values and the scale factor, d3.event.transform.k, so you just need to divide everything by the scale factor:

  let dx = d3.event.transform.x / d3.event.transform.k;
  let dy = d3.event.transform.y / d3.event.transform.k;
  let minimapRect = minimap.append('rect')
      .attr('id', 'minimapRect')
      .attr('width', mapWidth / factor / d3.event.transform.k )
      .attr('height', mapHeight / factor / d3.event.transform.k )
      .attr('stroke', 'red')
      .attr('fill', 'black')
      .attr('transform', `translate(${-dx},${-dy})`);
user_2052070

I found another way of achieving the same results using d3.zoomIdentity.scale. Working example 

function zoomed() {
      let transform = d3.event.transform;
      let modifiedTransform = d3.zoomIdentity.scale( 1/transform.k ).translate( -transform.x, -transform.y );

      let mapMainContainer = map.select('#main_container')
         .attr('transform', transform);


      minimapRect
          .attr('width', mapMainContainer.node().getBBox().width )
          .attr('height', mapMainContainer.node().getBBox().height )
          .attr('stroke', 'red')
          .attr('stroke-width', 10/modifiedTransform.k )
          .attr('stroke-dasharray', 10/modifiedTransform.k )
          .attr('fill', 'none')
          .attr('transform', modifiedTransform);
   }
user_11995940
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