Bezier Curve 101

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  <title>Dynamic Annotations in a Visualization Stepper</title>
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svg {
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</style>
<body>
  <div id="container">
    <h1>Albany Tableau Users Group: Bezier Curve 101</h1>
    <p>
	Bezier curves are commonly used in graphic design to draw smooth curves.  By creating additional data points within Tableau for each 'real' data point, math can be used to implement the bezier curve using data to define the starting point, ending point, and control points defining the curve.  The following sequence of examples shows how a single curve is implemented, how it can be used to visualize political terms, and how it can be tweaked to show different shaped arcs like golf drives.<div id="vis-nav">
      <a href="#" id="step0" class="step-link active">Bezier Curve Animation</a><a href="#" id="step1" class="step-link">Tableau Implementation</a><a href="#" id="step2" class="step-link">Inverting the Curve</a><a href="#" id="step3" class="step-link">Supreme Court Tenure Data</a><a href="#" id="step4" class="step-link">Bezier Curve Re-creation</a><a href="#" id="step5" class="step-link">Modifying the Control Points</a>
    </div>
	
    <div id="vis-container">
		
		<div id="vis-canvas"></div>
	<div id="vis-bezier"></div>
			
		<div id="tableauBezier1"></div>

</div>
	</div>
  <script src="https://public.tableau.com/javascripts/api/tableau-2.min.js"></script>
	<script src="https://public.tableau.com/javascripts/api/tableau-2.2.1.min.js"></script>
  <script>
  
  var laststep = "step0";
  
	function tableauViz(url,htmlElement) {
	
		var placeholderDiv = document.getElementById("tableauBezier1");
			  
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		  viz = new tableau.Viz(placeholderDiv, url, options);
		  
	}
			
	tableauViz("https://public.tableau.com/views/TableauUsersGroupBezierCurves/BezierExample")
	
	sources = d3.selectAll("#container").append("div").append("p");
	
	
	
	
	
	
	
	
var w = 900,
    h = 650,
    t = .5,
    delta = .01,
    padding = 10,
    bezier = {},
    n = 4,
	line = d3.line().x(function(d){return d.x;}).y(function(d){return d.y;}),
    orders = [4];

var points = [
  {x: 0, y: 346},
  {x: 160, y: 169},
  {x: 84,y: 42}
];

var svgBezier = d3.select("#vis-bezier")
	.selectAll("svg")
    .data(orders)
	.enter()
	.append("svg")
    .attr("width", w + 2 * padding)
    .attr("height", h + 2 * padding)

svgBezier.append("rect").attr("width",w).attr("height",h).attr("fill","white")	
	
var vis = svgBezier.append("g")
    .attr("transform", "translate(" + padding + "," + padding + ")")

update();

vis.selectAll("circle.control")
    .data(function(d) { return points.slice(0, d) })
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    .attr("class", "control")
    .attr("r", 7)
    .attr("cx", x)
    .attr("cy", y)
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vis.selectAll("text.controltext")
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    .attr("dy", ".4em")
    .text(function(d, i) { return "P" + i });

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  update();
});

function update() {
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      .data(function(d) { return getLevels(d, t); });
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var circle = interpolation.selectAll("circle")
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var path = interpolation.selectAll("path")
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  path.attr("d", line);

var curve = vis.selectAll("path.curve")
      .data(getCurve);
	  
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	  console.log(curve);
	  
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function getLevels(d, t_) {
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  var x = [points.slice(0, d)];
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    x.push(interpolate(x[x.length-1], t_));
  }
  return x;
}

viz.getWorkbook().changeParameterValueAsync('Y2', 1);	  
		
			if (laststep!="step2"){
				d3.selectAll("#tableauBezier1").remove();
			    d3.selectAll("#vis-container").append("div").attr("id","tableauBezier1");
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			;}
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;}
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	  if (laststep!="step1") {
		  //Until I find a more efficient method, delete embedded Viz and add back with new URL. 
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		  d3.selectAll("#vis-container").append("div").attr("id","tableauBezier1");
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			;}
	
	  viz.getWorkbook().changeParameterValueAsync('Y2', -1);
	 	  }
		  
	  if (newStep=="step3"){

//Until I find a more efficient method, delete embedded Viz and add back with new URL. 
		  d3.selectAll("#tableauBezier1").remove();
		  d3.selectAll("#vis-container").append("div").attr("id","tableauBezier1");
		  tableauViz("https://public.tableau.com/views/TableauUsersGroupArcPlotData/BezierDataset")
		  
		}
		
			  
	  if (newStep=="step4"){

//Until I find a more efficient method, delete embedded Viz and add back with new URL. 
		  d3.selectAll("#tableauBezier1").remove();
		  d3.selectAll("#vis-container").append("div").attr("id","tableauBezier1");
		  tableauViz("https://public.tableau.com/views/TableauUsersGroupArcChartBezierRe-creation/ArcChartRe-creation")
		  
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	  if (newStep=="step5"){

//Until I find a more efficient method, delete embedded Viz and add back with new URL. 
		  d3.selectAll("#tableauBezier1").remove();
		  d3.selectAll("#vis-container").append("div").attr("id","tableauBezier1");
		  tableauViz("https://public.tableau.com/views/TableauUsersGroupGolfDriveViz/GolfDrivesViz")
		}
		
				
		
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