Convert an SVG element to a g element using d3.js

Question

I am using D3 in a page where my objective is to superimpose two groups of paths : I have the earth coastlines as a background map (imported from a GeoJSON file), and I want to superimpose an old map on it, which is a separate SVG : http://bl.ocks.org/bperel/9943623/250fc9af2e09bf176f6d510e0b59fe643d792287

The SVG loading went well, however I would like my two maps to be included inside the same SVG element : it will be easier if I want the maps to be panned or zoomed. The issue here is that the external SVG has a specific viewbox, so if I move its <g> elements to the other SVG, the coordinates get messy. Hence my question : is there a way to convert the 2nd SVG to a <g> element that I could include in the first SVG ? Maybe d3 knows how to do that but I couldn't find such a tool in the documentation.

Answer 1

If you are going to zoom/pan the superimposed SVG's, Include both svg's in a <g> container element and attach zoom behavior to the <g> container.

Essentually, you will have:

<svg id=topSVG>
<g id=container>
<svg id=projection1>
....
</svg>
<svg id=projection2>
....
</svg>
</g>
</svg>

Below is a snippet relating to my mouswheel zoom for d3:

var myZoom=d3.behavior.zoom().scaleExtent([.1, 1000]).on("zoom", mouseWheelZoom)

function callZoomBehavior()
{
    //---attach to root svg---
    d3.select("#"+SVGId)
    .call(myZoom)
    //---reset from previous file call---
    myZoom.translate([0,0])
    myZoom.scale(1)
    PrevScale=1
}

var PrevScale //--previous scale event---
function mouseWheelZoom()
{
    //--place in d3 object--
    var zoomG=d3.select("#topZoomG")
    if(PrevScale!=d3.event.scale) //--transition on scale change--
    {
        zoomG.transition().attr("transform", "translate(" + d3.event.translate + ")scale(" + d3.event.scale + ")")
    }
    else //--no transition on pan---
    {
        zoomG.attr("transform", "translate(" + d3.event.translate + ")scale(" + d3.event.scale + ")")
    }
    PrevScale=d3.event.scale
}

Answer 2

originalSVG = the SVG element you want to clone and convert into g element quasiClone = the result of that parentOfClone = parent below you want to put your new g element

    var quasiClone = parentOfClone.append("g");
    for (var i=0; i<originalSVG.childNodes.length; i++){
        var child = originalSVG.childNodes[i];
        var childClone = child.cloneNode(true);
        quasiClone.node().appendChild(childClone);
    }