Difference between revisions of "Real-time graphing"

From JSXGraph Wiki
Jump to: navigation, search
m
Line 9: Line 9:
 
This little script shows how to graph the data from a sensor in a web browser.
 
This little script shows how to graph the data from a sensor in a web browser.
 
Using AJAX, the web browser retrieves once per second data from the web server by calling the script ''fakesensor.php''.
 
Using AJAX, the web browser retrieves once per second data from the web server by calling the script ''fakesensor.php''.
In this example just a random number is produced on server side.
+
 
 +
Here, ''fakesensor.php'' just returns a random number, but one can image that real sensor data can be accessed similarly.
 
<jsxgraph width="647" height="400">
 
<jsxgraph width="647" height="400">
 
var brd, g,  
 
var brd, g,  

Revision as of 10:07, 15 May 2010

This little script shows how to graph the data from a sensor in a web browser. Using AJAX, the web browser retrieves once per second data from the web server by calling the script fakesensor.php.

Here, fakesensor.php just returns a random number, but one can image that real sensor data can be accessed similarly.

The underlying JavaScript code

  <script type="text/javascript" src="http://jsxgraph.uni-bayreuth.de/distrib/prototype.js"></script>
  <style>
    #jxgbox {
       background-color:black;
    }
  </style>
var brd, g, 
    xdata = [], ydata = [],
    turt,i;

brd = JXG.JSXGraph.initBoard('jxgbox', {axis:true, boundingbox:[0,20,30,-2]});

turt = brd.createElement('turtle',[],{strokecolor:'#999999'});
turt.hideTurtle().right(90);
for (i=5;i<=15;i+=5) {
    turt.penUp().moveTo([0,i]).penDown().forward(30);
}


fetchData = function() {
    new Ajax.Request('/ajax/fakesensor.php', {
        onComplete: function(transport) {
            var t, a;
            if (200 == transport.status) {
                t = transport.responseText;
                a = parseFloat(t);
                if (xdata.length<30) {          
                    xdata.push(xdata.length); // add data to the x-coordinates, if the right border has not been reached, yet
                } else {
                    ydata.splice(0,1);        // remove the oldest entry of the y-coordinates, to make the graph move.
                }
                ydata.push(a);
                if (!g) {                   // If the curve does not exist yet, create it.
                    g = brd.createElement('curve', [xdata,ydata],{strokeWidth:3, strokeColor:'yellow'}); 
                } 
                brd.update();
            };
    }});
};
setInterval(fetchData,1000);  // Start the periodical update

The PHP code of fakesensor.php

<?php
   echo mt_rand(0,20);
?>