Category Archives: web development

Scroll an IFRAME Content to a Predefined Position

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IFRAME Source

Usually when you use an IFRAME tag to link an external source the page that’s referenced by the SRC attributes is loaded at the top left corner. This is the default behavior, but sometimes you’d like to show to your users not the entire page from the top left corner, but to show only part of the external page instead.

In most of the cases the reference is external and you don’t have control over the external page. Thus you’ve to scroll the IFRAME content to the desired position. This of course is impossible. Yeah, there are some JavaScript hacks, but they’re all a bad solution, because the scrolling occurs only after the page is loaded.

The Solution

You can wrap the IFRAME into a div and scroll the DIV content using absolute TOP and LEFT CSS properties.

Here’s an example:

#my-div
{
    width    : 400px;
    height   : 200px;
    overflow : hidden;
    position : relative;
}
 
#my-iframe
{
    position : absolute;
    top      : -100px;
    left     : -100px;
    width    : 1280px;
    height   : 1200px;
}

Here you have one DIV with dimensions 400x200px. Now by moving the IFRAME within it you can position it on the right place.

<div id="my-div">
<iframe src="http://www.example.com" id="my-iframe" scrolling="no"></iframe>
</div>

Continue reading Scroll an IFRAME Content to a Predefined Position →

How to Collect the Images and Meta Tags from a Webpage with PHP

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Meta Tags and the Facebook Example

You’ve definitely seen the “share a link” screen in Facebook. When you paste a link into the box (fig. 1) and press the “Attach” button you’ll get the prompted cite parsed with a title, description and possibly thumb (fig. 2). This functionality is well known in Facebook, but it appears to be well known also in various social services. In fact Linkedin, Reddit, Dzone‘s bookmarklet use it.

Facebook Attach a Link Prompt Screen
fig. 1 - Facebook Attach a Link Prompt Screen

Fist thing to notice is that this information, prompted by Facebook, is the same as the meta tag information. However there is a slight difference.

Facebook Attached Link Screen
fig. 2 - Facebook Attached Link Screen

Facebook prefers for the thumb the image set into the <meta property=”og:image” … />. In the case above this tag appears to be:

<meta property="og:image" content="http://b.vimeocdn.com/ts/572/975/57297584_200.jpg" />

And the image pointed in the SRC attribute is exactly the same as the one prompted by Facebook (fig. 3).

Vimeo Thumb
fig. 3 - Vimeo Thumb

First thing to note is that the real thumb is bigger than the thumb shown in Facebook, so Facebook resizes it and the second thing to note is that there are more meta tags of the og:… format. Continue reading How to Collect the Images and Meta Tags from a Webpage with PHP →

From SVG to Geo Coordinates – A Complete Guide

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Why This Task Is Not Trivial?

First of all what do we have? There is a vector shape, which may represent a map, which we’d like to convert into a GEO map. In other words there is a SVG file containing the source shape, that you’d like to convert in geoJSON or whatever collection of geo points. This is not trivial, of course, first of all because there’s no an algorithm or automation that can do this, and because everybody knows that the resulting map will be only approached, but will never be so accurate as the vector shape. This is because in a vector shape you may contain Bézier Curves, which I’ll show a little bit later in this post, that are difficult to represent in geo coordinates.

So the first task will be to find an approaching algorithm. However there are two things that are optimistic:

  1. You can’t effectively represent Bézier curves in geo coordinates, but even if you could do it there’s no practical need, because the collection of geo coordinates will be huge and this will slow down you’re application. Remember that geoJSON is yet again possibly used by your browser and the amount of geo points will be proportionally slowing down the app.
  2. As you may know Google’s visualization map is representing the World’s countries again with quite approached maps. Take a look at the following image – the country borders are quite sharpened:

Google Visualization Map

So far we know that we need an approaching algorithm that will convert vector lines and possibly curves in geo coordinates, but before we proceed we’ve to understand the SVG format. Continue reading From SVG to Geo Coordinates – A Complete Guide →

Wanted – onfocus/onblur. Why They Don’t Work Always!

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On Focus

onfocus

Perhaps you think of onfocus and onblur events as a default behavior existing in any web page. This is not quite true! Onfocurs and onblur are well known in web developing (js) and are fired, of course, when the user tries to point something or leaves some element. Onfocurs is fired when the user either goes to an element with the Tab button on with the mouse. When the element is on focus, evidently, the onfocus event is fired. Actually you can see which element is on focus, like an anchor or input, when the element is outlined by the browser by default. In the same scenario, when some element has been on focus and than the user switches to another element, the onblur event is fired. Thus you may guess that this element is no longer on focus. Continue reading Wanted – onfocus/onblur. Why They Don’t Work Always! →

Reading GPS Latitude and Longitude from Image and Video Files

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The State of GPS Data from Mobile Devices

Most of the mobile devices today support GPS geo tagging. In fact most of them come bundled with navigation software that uses GPS and therefore all the pictures and (maybe) videos can be geo tagged. But as expected different vendors come with different support and formats.



iPhone OS comes with geotagging both on video and image files, while the latest Android and Symbian (the Nokia main OS for smartphones) can geo tag only images.

Even more – until recently Symbian didn’t support any geotagging before the installation of an additional software – such as Location Tagger . So generally the things are quite simple:

  1. iPhone OS geotags both video and image files;
  2. Android geotags only images;
  3. Symbian geotags only images – and on some devices this is possible only after installing a software;

This is in breve the state of mobile device geotagging! Continue reading Reading GPS Latitude and Longitude from Image and Video Files →