tide currents fourier interpolation debug

Fourier Interpolation

Debugging a Fourier Interpolation of NOAA currents data.

<!DOCTYPE html>
<head>
  <meta charset="utf-8">
  <title>Bay Water Trail Tide Chart</title>
  <style>
    #tidal-chart {
      padding: 25px;
    }
    .zero-line path {
      stroke-width: 0;
      stroke: none;
    }
    .zero-line .tick line {
      stroke: grey;
    }
    .grid line {
      stroke: lightgrey;
      stroke-opacity: 0.7;
      shape-rendering: crispEdges;
    }

.grid path {
      stroke-width: 0;
    }
    .line {
      fill: none;
      stroke: steelblue;
      stroke-width: 2px;
    }
    .area { fill: lightsteelblue; }
    .tide-chart-title,
    text {
      font-family: sans-serif;
    }
    text { font-size: 13px; }
  </style>
</head>
<body>
<div class="loading-msg"><h3>Loading...</h3></div>
<div id="tidal-chart"></div>
<script src="https://d3js.org/d3.v4.min.js"></script>
<script src="https://unpkg.com/fourier@0.2.1/fourier.js"></script>
<script>

//
// This example interpolates values using a Fourier Transformation interpolation
// with help from Philippe Rivière's block: https://bl.ocks.org/Fil/6e83bb512f22ec579f6226b7692530fb
//

var loadingMsg = d3.select('.loading-msg');
var chartContainer = "#tidal-chart";
var margin = { top: 20, right: 20, bottom: 50, left: 50 };
var width = 900 - margin.left - margin.right;
var height = 420 - margin.top - margin.bottom;

// date time parser
var parseTime = d3.timeParse('%Y-%m-%d %I:%M %p');
var formatTime = d3.timeFormat('%B %d %I:%M%p');

// callback which is invoked upon data load finishing
function main(err, rsp) {
  if (err) throw err;

// this is a 3 year dataset, so only grab data for close to today's date
  var today = new Date();
  var beforeToday = +today - (1000 * 60 * 60 * 12);
  var tommorrow = +today + (1000 * 60 * 60 * 24);
  var data = rsp.filter(function(d) {
    return +parseTime(d.date_time) >= beforeToday && +parseTime(d.date_time) <= tommorrow;
  })
  .map(function(d) {
    d.date_time = +parseTime(d.date_time);
    d.speed = +d.speed;
    return d;
  });

console.log(data);

// x & y scales
  var x = d3.scaleLinear()
    .domain(d3.extent(data.map(d => d.date_time)))
    .range([0, width]);

var xlabel = d3.scaleTime()
    .domain(d3.extent(data.map(d => new Date(d.date_time))))
    .range([0, width]);

// TO DO: pad the domain so the curve doesn't touch the bottom or top of the chart
  var y = d3.scaleLinear()
    .domain(d3.extent(data.map(d => d.speed)))
    // .domain([-0.6, 0.6])
    .range([height, 0]);

// compute the Fast Fourier transform
  const a = data.filter(d => d.event !== 'slack'),
        points = 256,
        c = points / a.length,
        d = points / data.length,
        f = fourier.dft(a.map((d, i) => d.speed), a.map((d, i) => 0)),
        zeros = d3.range(points - f[0].length).map(d => 0),
        h = [ [...zeros,...f[0]], [...zeros,...f[1]]],
        g = fourier.idft(...h);

// interpolate the values
  function inter(i) {
    return c * (g[0][i] || 0)
  }

// interpolate the time
  var t = d3.scaleLinear()
    .domain(d3.range(data.length))
    .range(data.map(d => d.date_time));

var line = d3.line()
    .x(i => x(t(i / d)))
    .y(i => y(inter(i)));

// gridlines in x axis function
  function make_x_gridlines() {
    return d3.axisBottom(x).ticks(7)
  }

// gridlines in y axis function
  function make_y_gridlines() {
    return d3.axisLeft(y).ticks(5)
  }

// create chart title with current date from data
  // TO DO: add human readable name for station using look up table
  var title = d3.select(chartContainer).append('h3')
    .attr('class', 'tide-chart-title')
    .text('NOAA Current Predictions for SFB1213 on ' + formatTime(new Date()));

// create the svg element with an offset group element
  var svg = d3.select(chartContainer).append('svg')
      .attr('width', width + margin.left + margin.right)
      .attr('height', height + margin.top + margin.bottom)
    .append('g')
      .attr('transform', 'translate(' + margin.left + ',' + margin.top + ')');

// x-axis
  svg.append('g')
    .attr('transform', 'translate(0,' + height + ')')
    .call(d3.axisBottom(xlabel));

// y-axis
  svg.append('g')
    .call(d3.axisLeft(y));

// add the X gridlines
  svg.append("g")
      .attr("class", "grid grid-x")
      .attr("transform", "translate(0," + height + ")")
      .call(make_x_gridlines()
          .tickSize(-height)
          .tickFormat("")
      );

// add the Y gridlines
  svg.append("g")
      .attr("class", "grid grid-y")
      .call(make_y_gridlines()
          .tickSize(-width)
          .tickFormat("")
      );

// add line for showing "0" y-axis value
  svg.append('g')
    .attr('class', 'zero-line')
    .call(d3.axisLeft(y).ticks(1).tickFormat('').tickSize(-width));

// create the line path
  svg.append('path')
    .attr('fill', 'none')
    .attr('stroke', 'steelblue')
    .attr('d', line(d3.range(points)));

// add reference circles
  svg.selectAll('circle')
    .data(data)
    .enter()
    .append('circle')
    .attr('r', 4)
    .attr('cx', d => x(d.date_time))
    .attr('cy', d => y(d.speed))

// y axis label
  svg.append('text')
    .attr('text-anchor', 'middle')
    .attr('transform', 'translate(' + (-margin.left + 12) + ',' + (height / 2) + ') rotate(-90)')
    .text('Speed (Knots)');

// x axis label
  svg.append('text')
    .attr('text-anchor', 'middle')
    .attr('transform', 'translate(' + (width / 2) + ',' + (height + (margin.bottom - 10)) + ')')
    .text('Time of Day');

// hide our loading message
  loadingMsg.style('display', 'none');
}

// get the data & then make the chart
d3.csv('SFB1213.csv', main);
  
</script>
</body>
</html>

https://d3js.org/d3.v4.min.js

https://unpkg.com/fourier@0.2.1/fourier.js