HTML5 Canvas Map Clickaround Overlay Tutorial

HTML5 Canvas Map Clickaround Overlay Tutorial

After some time in the (PHP) server world, it’s time to dive back into some client (Javascript and HTML) work, in this client/server world of web applications.

Today we revisit the “overlay” theme of blog postings, as the web application world is full of possibilities for overlay ideas.

This time we overlay an HTML div element completely on top of an HTML canvas element, with some opacity (or some transparency), during the body “onload” event. We do not adjust the DOM “z-index” style property for either element. So what happens in this scenario when you click on this “multiple” HTML element combination? Well, it pans out you click on the HTML div element, so we have another task to do at the body “onload” event, to see things right, regarding the working of this web application, which starts where we left off with HTML5 Canvas Map Clickaround Follow Up Tutorial as shown below.

From this basis, this is how we got to today … there was HTML cloudy_world.html that changed like here.

You’ll see in the code above some great code presented at useful link (thanks) which is great for defining an HTML element’s size via …


function SetBox(what) {
var div = document.getElementById(what);
if (div.getBoundingClientRect) { // Internet Explorer, Firefox 3+, Google Chrome, Opera 9.5+, Safari 4+
// do stuff
}
}


… and we hope you can see that the implications for “overlay” ideas you have are huge … and that is fine … but you may wonder how the HTML div element is made to drape right over all the canvas element … well, it uses styling as per …

• position: absolute;
• top and left and width and height parameters are all defined
• borderTop defined as having a size the same as height above as per our HTML div id=’boxdiv’ element …
  
document.getElementById('boxdiv').style.position = 'absolute';
document.getElementById('boxdiv').style.top = y + "px";
document.getElementById('boxdiv').style.left = x + "px";
document.getElementById('boxdiv').style.width = w + "px";
document.getElementById('boxdiv').style.height = h + "px";
document.getElementById('boxdiv').style.borderTop = h + 'px solid rgba(255,255,255,0.5)';


… and you’ll also see with the code how the HTML div id=’boxdiv’ element’s “onclick” details are transferred to the (effectively underlying) HTML canvas element, where all the previous business logic of the web application resided, and continues to function (once you make variables “x” and “y” global and control how they are derived at the HTML div id=’boxdiv’ element’s “onclick” event logic).

So please try the live run to see all this in action.

Previous relevant HTML5 Canvas Map Clickaround Follow Up Tutorial is shown below.

HTML5 Canvas Map Clickaround Follow Up Tutorial

HTML5 brought in the incredibly useful “canvas” element, for the first time. Its existence opens up a whole new world of possibilities for web applications that are graphical by nature, as we saw yesterday with HTML5 Canvas Map Clickaround Primer Tutorial as shown below. Today, we extend that functionality as of yesterday, by adding the use of a public data feed to enhance the information we present with the Google Map “iframe” we use, and for this we need to thank, profusely, The Global Airport Database project by Arash Partow … thanks very much. Now this database (really a file), as you can imagine, has data that changes over time, so is probably best used as a data feed. Nevertheless, the exercise of using it as a snapshot is useful, and we go ahead and show the nearest 4 airports on the database, in that Google Map “iframe” as of April, 2015.

This involved the use of PHP (intair.php) to read the file and parse it, which wasn’t hard as it contains well formed “:” delimited data, and there is just the check needed for security hidden data given a latitude and longitude of zero … unless I’m mistaken, and where the water goes down the sink the other way as you cross the equator due south of London has several hundred microscopic airports run by ants … what a movie script?!

With the canvas element’s drawImage() method, we use to position the image map of interest, you can draw more than your own geometrical constructs, you can have an image, and that image could be a map, as for today’s “World Clickaround” web application (with access to maps of Brazil and Ireland and United States of America too), where you click on the map (and thanks to mapsofworld.com for downloadable free maps here) to show a Google Map of interest via Google Chart Map Chart. Maybe you can use the map of the World to …

• plan a trip
• look up where relatives live
• count the fire hydrants in Monaco

This web application calls on tiny bits of mapping knowledge, namely the “orientation” of your “map”, as you are effectively digitizing to show where you want your Google Map to zoom in on.

Please have a go of our live run or download the HTML programming source code you could call world.htm (brazil.htm, ireland.htm, united_states.htm), or do both?!

From yesterday, this is how we got to today … there was new PHP you could call intair.php … and then there was changed HTML, the changes for which look like … world.htm, brazil.htm, ireland.htm, united_states.htm

Previous relevant HTML5 Canvas Map Clickaround Primer Tutorial is shown below.

HTML5 Canvas Map Clickaround Primer Tutorial

HTML5 brought in the incredibly useful “canvas” element, for the first time. Its existence opens up a whole new world of possibilities for web applications that are graphical by nature.

With the canvas element’s drawImage() method you can draw more than your own geometrical constructs, you can have an image, and that image could be a map, as for today’s “Ireland Clickaround” web application (with access to maps of Brazil and United States of America and the World too), where you click on the map (and thanks to mapsofworld.com for downloadable free maps here) to show a Google Map of interest via Google Chart Map Chart. Maybe you can use the map of Ireland to …

• plan a trip
• look up where relatives live
• imagine you’re in O’Connell Street

This web application calls on tiny bits of mapping knowledge, namely the “orientation” of your “map”, as you are effectively digitizing to show where you want your Google Map to zoom in on.

This is one of those occasions that your (simple) software is a lot more effective using the Mercator map projection (that exaggerates the polar areas (like you might have had at school) because the simple latitude and longitude distances everywhere are the same (but relative areas definitely are not (ie. much bigger than reality near the poles))). Unfortunately, our United States of America projection is not Mercator, but you’ll still get a “ball park” Google Maps feel.

So we can have it that if the user doesn’t zoom, they need no orientation checks, but otherwise we need to determine a scale, by the user clicking on Dublin, on the map, and from that, we can work out the scaling that needs to be applied, as the top left co-ordinate is arranged to be (0,0) via the style=”position: absolute; top:0; left:0; “ part of …


<canvas id="canvaselement" width=600 height=600 style="position: absolute; top:0; left:0; " />


Please have a go of our live run or download the HTML programming source code you could call ireland.html (brazil.html, united_states.html, world.html), or do both?!

If this was interesting you may be interested in this too.

If this was interesting you may be interested in this too.

If this was interesting you may be interested in this too.