interpolate latitude and longitude

D3を使って２点間の緯度経度を補完し、トランジションさせる。

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<meta http-equiv="X-UA-Compatible" content="IE=edge"/>
<title></title>
<link rel="stylesheet" href="//cdnjs.cloudflare.com/ajax/libs/leaflet/0.7.7/leaflet.css"/>
<style>
html, body {
    padding: 0px;
    margin: 0px;
}
    
html, body, #map {
    width: 100%;
    height: 100%;
}
.tick line {
    stroke-dasharray: 2 2 ;
    stroke: #ccc;
}

#interface {
    position: absolute;
    top:10px;
    left: 40px;
    width: 308px;
    height: 28px;
    padding: 4px;
    background-color: white;
    z-index: 9999;
    
}
#interface button {
    color:white;
    background-color: blue;
}
</style>

</head>

<body>
<div id="interface">
<select id="ease-type">
    <option>easeLinear</option>
    <option>easeElastic</option>
    <option>easeBounce</option>
    <option>easeSin</option>
    <option>easeQuad</option>
    <option>easeCubic</option>
    <option>easePoly</option>
    <option>easeCircle</option>
    <option>easeExp</option>
    <option>easeBack</option>
</select>
<input id="duration" type="number" value="1500"></input>
<button id="startBtn">transition</button>
    
</div>    
    
<div id="map"></div>    
    
    
    
<script src="//cdnjs.cloudflare.com/ajax/libs/d3/4.1.1/d3.min.js"></script>    
<script src="//cdnjs.cloudflare.com/ajax/libs/leaflet/0.7.7/leaflet-src.js"></script>
<script>
!(function(){
    "use strict"
    
    var map //leaflet obj
    
    var soruce = {
        lat:36.3219088,
        lng:139.0032936,
    }

//Leafletに用意されたsvgを使う 
        map._initPathRoot();	
        
    }
    
    //位置→座標変換
    function projectPoint(x, y) {
        var point = map.latLngToLayerPoint(new L.LatLng(y, x));
        return point;
    }
    
    function renderCircle() {
        var svg = d3.select("#map").select("svg");
        
    
        var circle = svg.append("circle")
            .datum(data)
            .attr("stroke", "gray")
            .attr("fill", "red")
            .attr("fill-opacity", 0.6)
            .attr("r", 20)
            .on("click", function(d){
                moveTween(d.soruce, d.target, 3000, d3.easeBounce)
            })
    
        map.on("viewreset", update);
        update();
        
        //サークルを地図上でトランジションさせる。
        d3.select("#startBtn").on("click", function(){
            var easeType = document.querySelector("#ease-type").value;
            var duration = document.querySelector("#duration").value;
            reset();
  
            moveTween(data.soruce, data.target, duration, d3[easeType]);
        })
    
        //緯度経度を画面座標に変換してcircleの位置を移動する
        function update() {		
            circle.attr("transform", function(d){
                var p = projectPoint(d.current.lng, d.current.lat);
                return "translate("+[p.x,p.y]+")";
            });
        }
        
        //位置をリセット
        function reset(){
                data.current.lat = data.soruce.lat;
                data.current.lng = data.soruce.lng;

circle.datum(data);
                update();            
        }
        
        //2点間の緯度経度を補完する
        function moveTween(soruce, target, duration, ease) {
            if(!ease) ease = d3.easeLinear;
            var scale = d3.scaleLinear().domain([0, duration]).range([0, 1]).clamp(true);
        
            var interpolateLat = d3.interpolate(soruce.lat, target.lat);
            var interpolateLng = d3.interpolate(soruce.lng, target.lng);
        
        
            var t = d3.timer(function(elapsed) {
                var c = ease(scale(elapsed));
                
                data.current.lat = interpolateLat(c);
                data.current.lng = interpolateLng(c);

circle.datum(data);
                
                update()
        
                if (elapsed > duration) t.stop();
            }, 100);
        
        }        
    
    }
    
        
}());
</script>    
</body>
</html>

https://cdnjs.cloudflare.com/ajax/libs/d3/4.1.1/d3.min.js

https://cdnjs.cloudflare.com/ajax/libs/leaflet/0.7.7/leaflet-src.js