Create Elevation profile from polyline coordinate array

Question

I have created a polyline using a coordinate array with code adapted from https://google-developers.appspot.com/maps/documentation/javascript/examples/polyline-simple

Although the first (and probably worst) method to make the line was just a huge list of lat/lng points. Still learning the programming tricks, I apologize. Im a geographer not a programmer!

I want to get the elevation from that line and create an elevation profile graph. Im new to JS and not sure how to debug whats not working. I cant seem to populate the path array with the coordinates from the polyline.

Its currently set to push the bikeCourseCoordinates to a new array that will then be used as a path. I tried it just using the bikeCourseCoordinates array as the 'path' but that didnt work either.

Online (but not working version) here: http://geography.uoregon.edu:50000/bentesting/map_try3.html

function drawPath() {

  // Create a new chart in the elevation_chart DIV.
  chart = new google.visualization.ColumnChart(document.getElementById('elevation_chart'));

  var path = new Array;
  path.push(bikeCourseCoordinates);


  // Create a PathElevationRequest object using this array.
  var pathRequest = {
    'path': path,
    'samples': 256
  }

  // Initiate the path request.
  elevator.getElevationAlongPath(pathRequest, plotElevation);
}

// Takes an array of ElevationResult objects, draws the path on the map
// and plots the elevation profile on a Visualization API ColumnChart.
function plotElevation(results, status) {
  if (status == google.maps.ElevationStatus.OK) {
    elevations = results;

    // Extract the elevation samples from the returned results
    // and store them in an array of LatLngs.
    var elevationPath = [];
    for (var i = 0; i < results.length; i++) {
      elevationPath.push(elevations[i].location);
    }

    // Extract the data from which to populate the chart.
    // Because the samples are equidistant, the 'Sample'
    // column here does double duty as distance along the
    // X axis.
    var data = new google.visualization.DataTable();
    data.addColumn('string', 'Sample');
    data.addColumn('number', 'Elevation');
    for (var i = 0; i < results.length; i++) {
      data.addRow(['', elevations[i].elevation]);
    }

    // Draw the chart using the data within its DIV.
    document.getElementById('elevation_chart').style.display = 'block';
    chart.draw(data, {
      width: 640,
      height: 200,
      legend: 'none',
      titleY: 'Elevation (m)'
    });
  }
}

score 3 · Answer 1 · answered Jul 22 '12 at 22:21

Are you trying to reproduce the third exemple on that page ? https://developers.google.com/maps/customize

If yes i have done it but without the graph over effects

here is my code

this goes in your head

script type="text/javascript" src="http://maps.google.com/maps/api/js?sensor=true"
script type="text/javascript" src="https://www.google.com/jsapi"
script src="https://www.google.com/uds/?file=visualization&amp;v=1&amp;packages=columnchart" type="text/javascript"

and this in the footer just before body tag

var elevator;
var map;
var chart;
var infowindow = new google.maps.InfoWindow();
var polyline;
var mapCenter = new google.maps.LatLng(-21.745585792425,165.91141052497);


// Load the Visualization API and the columnchart package.
google.load("visualization", "1", {packages: ["columnchart"]});


function initialize() {
    var mapOptions = {
        center: mapCenter,
        zoom: 13,
        mapTypeId: 'terrain'
    };

    map = new google.maps.Map(document.getElementById("map"), mapOptions);

    // Create an ElevationService.
    elevator = new google.maps.ElevationService();

    // Draw the path, using the Visualization API and the Elevation service.
    drawPath();
}


function drawPath() {

    // Create a new chart in the elevation_chart DIV.
    chart = new google.visualization.ColumnChart(document.getElementById('elevation-chart'));

    var path = bikeCourseCoordinates;

    // Create a PathElevationRequest object using this array.
    // Ask for 256 samples along that path.
    var pathRequest = {
        'path': path,
        'samples': 256
    }

    // Initiate the path request.
    elevator.getElevationAlongPath(pathRequest, plotElevation);
}



function plotElevation(results, status) {
  if (status == google.maps.ElevationStatus.OK) {
    elevations = results;

    // Extract the elevation samples from the returned results
    // and store them in an array of LatLngs.
    var elevationPath = [];
    for (var i = 0; i < results.length; i++) {
      elevationPath.push(elevations[i].location);
    }

    // Display a polyline of the elevation path.
    var pathOptions = {
      path: elevationPath,
      strokeColor: '#0000CC',
      opacity: 0.9,
      map: map
    }
    polyline = new google.maps.Polyline(pathOptions);

    // Extract the data from which to populate the chart.
    // Because the samples are equidistant, the 'Sample'
    // column here does double duty as distance along the
    // X axis.
    var data = new google.visualization.DataTable();
    data.addColumn('string', 'Sample');
    data.addColumn('number', 'Elevation');
    for (var i = 0; i < results.length; i++) {
      data.addRow(['', elevations[i].elevation]);
    }

    // Draw the chart using the data within its DIV.
    document.getElementById('elevation-chart').style.display = 'block';
    chart.draw(data, {
      width: 960,
      height: 300,
      legend: 'none',
      titleY: 'Elevation (m)'
    });
  }
}



initialize();

score 0 · Answer 2 · answered Jun 13 '12 at 05:57

I couldn't find the problem but here are some observations which might help:

I tried it just using the bikeCourseCoordinates array as the 'path'

According to the Maps API, pathRequest should be be:

var pathRequest = {
    'path': bikeCourseCoordinates,
    'samples': 256
}

Further, I think the following initial part, ie:

var whitney = new google.maps.LatLng(36.578581, -118.291994);
...
...
var panamintsprings = new google.maps.LatLng(36.339722, -117.467778);
var badwater = new google.maps.LatLng(36.23998, -116.83171);

var bikeCourseCoordinates = [
            new google.maps.LatLng(47.67609435030702, -116.7896032333374),

which comes directly within the first inline <script> tag should be called only after the maps library is loaded. I would put it all into another function say myInit and then call myInit from within your current function named initialize

The reason for this above is that although you are including the script tag to include the maps api maps.googleapis.com/maps/api/js?sensor=false the browser will continue to execute the next script block containing whitney= new google.maps.Lat because maps.googleapis.com is an external script and I think these external scripts are loaded asynchronously.

Create Elevation profile from polyline coordinate array

2 Answers2

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