Raster Source

This example uses OpenLayers v4.0.1. The latest is v.

#### Raster Source

Demonstrates pixelwise operations with a raster source.

This example uses a `ol.source.Raster` to generate data based on another source. The raster source accepts any number of input sources (tile or image based) and runs a pipeline of operations on the input pixels. The return from the final operation is used as the data for the output source.

In this case, a single tiled source of imagery is used as input. For each pixel, the Vegetation Greenness Index (VGI) is calculated from the input pixels. A second operation colors those pixels based on a threshold value (values above the threshold are green and those below are transparent).

Related API documentation:

- ol.Map
,
- ol.View
,
- ol.layer.Image
,
- ol.layer.Tile
,
- ol.source.BingMaps
,
- ol.source.Raster

Copy Edit
Raster Source Demonstrates pixelwise operations with a raster source. // this example uses d3 for which we don't have an externs file. var minVgi = 0; var maxVgi = 0.25; var bins = 10; /** * Calculate the Vegetation Greenness Index (VGI) from an input pixel. This * is a rough estimate assuming that pixel values correspond to reflectance. * @param {Array.<number>} pixel An array of [R, G, B, A] values. * @return {number} The VGI value for the given pixel. */ function vgi(pixel) { var r = pixel[0] / 255; var g = pixel[1] / 255; var b = pixel[2] / 255; return (2 * g - r - b) / (2 * g + r + b); } /** * Summarize values for a histogram. * @param {numver} value A VGI value. * @param {Object} counts An object for keeping track of VGI counts. */ function summarize(value, counts) { var min = counts.min; var max = counts.max; var num = counts.values.length; if (value < min) { // do nothing } else if (value >= max) { counts.values[num - 1] += 1; } else { var index = Math.floor((value - min) / counts.delta); counts.values[index] += 1; } } /** * Use aerial imagery as the input data for the raster source. */ var bing = new ol.source.BingMaps({ key: 'Your Bing Maps Key from http://www.bingmapsportal.com/ here', imagerySet: 'Aerial' }); /** * Create a raster source where pixels with VGI values above a threshold will * be colored green. */ var raster = new ol.source.Raster({ sources: [bing], /** * Run calculations on pixel data. * @param {Array} pixels List of pixels (one per source). * @param {Object} data User data object. * @return {Array} The output pixel. */ operation: function(pixels, data) { var pixel = pixels[0]; var value = vgi(pixel); summarize(value, data.counts); if (value >= data.threshold) { pixel[0] = 0; pixel[1] = 255; pixel[2] = 0; pixel[3] = 128; } else { pixel[3] = 0; } return pixel; }, lib: { vgi: vgi, summarize: summarize } }); raster.set('threshold', 0.1); function createCounts(min, max, num) { var values = new Array(num); for (var i = 0; i < num; ++i) { values[i] = 0; } return { min: min, max: max, values: values, delta: (max - min) / num }; } raster.on('beforeoperations', function(event) { event.data.counts = createCounts(minVgi, maxVgi, bins); event.data.threshold = raster.get('threshold'); }); raster.on('afteroperations', function(event) { schedulePlot(event.resolution, event.data.counts, event.data.threshold); }); var map = new ol.Map({ layers: [ new ol.layer.Tile({ source: bing }), new ol.layer.Image({ source: raster }) ], target: 'map', view: new ol.View({ center: [-9651695, 4937351], zoom: 13, minZoom: 12, maxZoom: 19 }) }); var timer = null; function schedulePlot(resolution, counts, threshold) { if (timer) { clearTimeout(timer); timer = null; } timer = setTimeout(plot.bind(null, resolution, counts, threshold), 1000 / 60); } var barWidth = 15; var plotHeight = 150; var chart = d3.select('#plot').append('svg') .attr('width', barWidth * bins) .attr('height', plotHeight); var chartRect = chart[0][0].getBoundingClientRect(); var tip = d3.select(document.body).append('div') .attr('class', 'tip'); function plot(resolution, counts, threshold) { var yScale = d3.scale.linear() .domain([0, d3.max(counts.values)]) .range([0, plotHeight]); var bar = chart.selectAll('rect').data(counts.values); bar.enter().append('rect'); bar.attr('class', function(count, index) { var value = counts.min + (index * counts.delta); return 'bar' + (value >= threshold ? ' selected' : ''); }) .attr('width', barWidth - 2); bar.transition().attr('transform', function(value, index) { return 'translate(' + (index * barWidth) + ', ' + (plotHeight - yScale(value)) + ')'; }) .attr('height', yScale); bar.on('mousemove', function(count, index) { var threshold = counts.min + (index * counts.delta); if (raster.get('threshold') !== threshold) { raster.set('threshold', threshold); raster.changed(); } }); bar.on('mouseover', function(count, index) { var area = 0; for (var i = counts.values.length - 1; i >= index; --i) { area += resolution * resolution * counts.values[i]; } tip.html(message(counts.min + (index * counts.delta), area)); tip.style('display', 'block'); tip.transition().style({ left: (chartRect.left + (index * barWidth) + (barWidth / 2)) + 'px', top: (d3.event.y - 60) + 'px', opacity: 1 }); }); bar.on('mouseout', function() { tip.transition().style('opacity', 0).each('end', function() { tip.style('display', 'none'); }); }); } function message(value, area) { var acres = (area / 4046.86).toFixed(0).replace(/\B(?=(\d{3})+(?!\d))/g, ','); return acres + ' acres at<br>' + value.toFixed(2) + ' VGI or above'; } .rel { position: relative } #plot { pointer-events: none; position: absolute; bottom: 10px; left: 10px; } .bar { pointer-events: auto; fill: #AFAFB9; } .bar.selected { fill: green; } .tip { position: absolute; background: black; color: white; padding: 6px; font-size: 12px; border-radius: 4px; margin-bottom: 10px; display: none; opacity: 0; } <div class="rel"> <div id="map" class="map"></div> <div id="plot"></div> </div>

    <!DOCTYPE html>
    <html>
      <head>
        <title>Raster Source</title>
        <link rel="stylesheet" href="https://openlayers.org/en/v4.0.1/css/ol.css" type="text/css">
        <!-- The line below is only needed for old environments like Internet Explorer and Android 4.x -->
        <script src="https://cdn.polyfill.io/v2/polyfill.min.js?features=requestAnimationFrame,Element.prototype.classList,URL"></script>
        <script src="https://openlayers.org/en/v4.0.1/build/ol.js"></script>
        <script src="https://d3js.org/d3.v3.min.js"></script>
        <style>
          .rel {
            position: relative
          }

          #plot {
            pointer-events: none;
            position: absolute;
            bottom: 10px;
            left: 10px;
          }

          .bar {
            pointer-events: auto;
            fill: #AFAFB9;
          }

          .bar.selected {
            fill: green;
          }

          .tip {
            position: absolute;
            background: black;
            color: white;
            padding: 6px;
            font-size: 12px;
            border-radius: 4px;
            margin-bottom: 10px;
            display: none;
            opacity: 0;
          }
        </style>
      </head>
      <body>
        <div class="rel">
          <div id="map" class="map"></div>
          <div id="plot"></div>
        </div>
        <script>
          // this example uses d3 for which we don't have an externs file.
          var minVgi = 0;
          var maxVgi = 0.25;
          var bins = 10;

          /**
           * Calculate the Vegetation Greenness Index (VGI) from an input pixel.  This
           * is a rough estimate assuming that pixel values correspond to reflectance.
           * @param {Array.<number>} pixel An array of [R, G, B, A] values.
           * @return {number} The VGI value for the given pixel.
           */
          function vgi(pixel) {
            var r = pixel[0] / 255;
            var g = pixel[1] / 255;
            var b = pixel[2] / 255;
            return (2 * g - r - b) / (2 * g + r + b);
          }

          /**
           * Summarize values for a histogram.
           * @param {numver} value A VGI value.
           * @param {Object} counts An object for keeping track of VGI counts.
           */
          function summarize(value, counts) {
            var min = counts.min;
            var max = counts.max;
            var num = counts.values.length;
            if (value < min) {
              // do nothing
            } else if (value >= max) {
              counts.values[num - 1] += 1;
            } else {
              var index = Math.floor((value - min) / counts.delta);
              counts.values[index] += 1;
            }
          }

          /**
           * Use aerial imagery as the input data for the raster source.
           */
          var bing = new ol.source.BingMaps({
            key: 'Your Bing Maps Key from http://www.bingmapsportal.com/ here',
            imagerySet: 'Aerial'
          });

          /**
           * Create a raster source where pixels with VGI values above a threshold will
           * be colored green.
           */
          var raster = new ol.source.Raster({
            sources: [bing],
            /**
             * Run calculations on pixel data.
             * @param {Array} pixels List of pixels (one per source).
             * @param {Object} data User data object.
             * @return {Array} The output pixel.
             */
            operation: function(pixels, data) {
              var pixel = pixels[0];
              var value = vgi(pixel);
              summarize(value, data.counts);
              if (value >= data.threshold) {
                pixel[0] = 0;
                pixel[1] = 255;
                pixel[2] = 0;
                pixel[3] = 128;
              } else {
                pixel[3] = 0;
              }
              return pixel;
            },
            lib: {
              vgi: vgi,
              summarize: summarize
            }
          });
          raster.set('threshold', 0.1);

          function createCounts(min, max, num) {
            var values = new Array(num);
            for (var i = 0; i < num; ++i) {
              values[i] = 0;
            }
            return {
              min: min,
              max: max,
              values: values,
              delta: (max - min) / num
            };
          }

          raster.on('beforeoperations', function(event) {
            event.data.counts = createCounts(minVgi, maxVgi, bins);
            event.data.threshold = raster.get('threshold');
          });

          raster.on('afteroperations', function(event) {
            schedulePlot(event.resolution, event.data.counts, event.data.threshold);
          });

          var map = new ol.Map({
            layers: [
              new ol.layer.Tile({
                source: bing
              }),
              new ol.layer.Image({
                source: raster
              })
            ],
            target: 'map',
            view: new ol.View({
              center: [-9651695, 4937351],
              zoom: 13,
              minZoom: 12,
              maxZoom: 19
            })
          });

          var timer = null;
          function schedulePlot(resolution, counts, threshold) {
            if (timer) {
              clearTimeout(timer);
              timer = null;
            }
            timer = setTimeout(plot.bind(null, resolution, counts, threshold), 1000 / 60);
          }

          var barWidth = 15;
          var plotHeight = 150;
          var chart = d3.select('#plot').append('svg')
              .attr('width', barWidth * bins)
              .attr('height', plotHeight);

          var chartRect = chart[0][0].getBoundingClientRect();

          var tip = d3.select(document.body).append('div')
              .attr('class', 'tip');

          function plot(resolution, counts, threshold) {
            var yScale = d3.scale.linear()
                .domain([0, d3.max(counts.values)])
                .range([0, plotHeight]);

            var bar = chart.selectAll('rect').data(counts.values);

            bar.enter().append('rect');

            bar.attr('class', function(count, index) {
              var value = counts.min + (index * counts.delta);
              return 'bar' + (value >= threshold ? ' selected' : '');
            })
            .attr('width', barWidth - 2);

            bar.transition().attr('transform', function(value, index) {
              return 'translate(' + (index * barWidth) + ', ' +
                  (plotHeight - yScale(value)) + ')';
            })
            .attr('height', yScale);

            bar.on('mousemove', function(count, index) {
              var threshold = counts.min + (index * counts.delta);
              if (raster.get('threshold') !== threshold) {
                raster.set('threshold', threshold);
                raster.changed();
              }
            });

            bar.on('mouseover', function(count, index) {
              var area = 0;
              for (var i = counts.values.length - 1; i >= index; --i) {
                area += resolution * resolution * counts.values[i];
              }
              tip.html(message(counts.min + (index * counts.delta), area));
              tip.style('display', 'block');
              tip.transition().style({
                left: (chartRect.left + (index * barWidth) + (barWidth / 2)) + 'px',
                top: (d3.event.y - 60) + 'px',
                opacity: 1
              });
            });

            bar.on('mouseout', function() {
              tip.transition().style('opacity', 0).each('end', function() {
                tip.style('display', 'none');
              });
            });

          }

          function message(value, area) {
            var acres = (area / 4046.86).toFixed(0).replace(/\B(?=(\d{3})+(?!\d))/g, ',');
            return acres + ' acres at<br>' + value.toFixed(2) + ' VGI or above';
          }
        </script>
      </body>
    </html>