Restore panoramas (cubic tiles) from exported Pano2VR

With this simple little script you can restore the full size cubic faces of the panorama which was exported using Pano2VR.

Pretty useful, if you deleted the original by mistake ;)

To convert the cubic projection back to equirectangular, you can also use Pano2VR, but for the input source you choose "Cubic", load all six cube faces, and export transformation.


Pano2VR's panoramas are exported as tiles in a cubic projection. The file naming scheme is as follows:
c[CUBE FACE]_l[RESOLUTION LEVEL]_[X]_[Y].jpg
for example:
c0_l0_0_0.jpg.

The most detailed resolution level is "0", so that level is used, and other tiles are disregarded.
Cube faces range from 0 to 5, and X and Y are the row and column number.

The script is written in PHP, and should be run in a CLI.

error_reporting(E_ALL);
ini_set('display_errors', 1);
ini_set('memory_limit', '2G');
date_default_timezone_set('Europe/Ljubljana');

$dir = 'tiles/';

foreach(range(0,5) as $c) {
 $i = 0;
 $tiles = array();
 $height = 0;
 do {
  $width = 0;
  $j = 0;
  do {
   $fn = fname($c,$i,$j);
   if(file_exists($fn)) {
    $tiles[$i][$j] = $fn;
    list($w, $h) = getimagesize($fn);
    $width += $w;
   }
   $j++;
  } while(file_exists(fname($c,$i,$j)));
  $j--;
  $i++;
  $height += $h;
 } while(file_exists(fname($c,$i,$j)));
 $i--;
 
 echo $width.' '.$height."\n";
 $im = imagecreatetruecolor($width, $height);
 $y = 0;
 foreach($tiles as $row) {
  $x = 0;
  foreach($row as $tile) {
   $tile = imagecreatefromjpeg($tile);
   $src_w = imagesx($tile);
   $src_h = imagesy($tile);
   imagecopy($im, $tile, $x, $y, 0, 0, $src_w, $src_h);
   $x += $src_w;
   imagedestroy($tile);
  }
  $y += $src_h;
 }
 imagejpeg($im, "$c.jpg", 70);
}

function fname($c,$i,$j) {
 global $dir;
 return "{$dir}c{$c}_l0_{$i}_{$j}.jpg";
}

Tiles

Restored cube faces

Restored panorama 

PHP :: Advice on using count()

I may be a little late realising this, but a few dozen thousand lines of PHP code in, it's better late than never.

Let's look at example #1 on count() manual
http://php.net/manual/en/function.count.php

$result = count(null); // $result == 0
$result = count(false); // $result == 1


Does this strike you as a bit odd? Why the hell should count(0) or count(false) be equal to 1?

Well strangely enough, that's how it is. So for example, if you wrote a mysql_query() wrapper where you return false if the query fails and if you expect an array where you check the number of items, you find out that if the query fails, the count will return 1, and you might get some unexpected results.

Keeping computer security in mind, it's best to avoid count() when just checking if some data is returned.

Alternatives are empty() if checks if a variable contains something other than 0, '0', null, false, array() or ''.

OR, in your wrapper functions, if the query fails, just return NULL!

Quick Tip: light switch effect

Here's a quick tip for novice programmers. Every time you want to create a "light-switch" effect for toggling a parameter on and off, or should I say true or false, 0 or 1, ... You can simply do it by typing:

p ^= 1;

This is a binary-safe Exclusive-OR assignment operator. First, it computes the value of p XOR 1 (p = p ^ 1) and then stores that value in p. If we look at the truth table of exclusive-or (XOR)

a	b	a XOR b
0	0	0
0	1	1
1	0	1
1	1	0

We see that if our b variable is 1 (true) the result of a ^ 1 (a XOR 1) is exactly the opposite of a. All in all, this operation is simply a shortcut for these assignments:

p = p ^ 1;

p = !p;

p = p ? false : true;

if(p) p = false; else p = true;

So if you want to toggle something ON and OFF, let's say when a user clicks a button, this method is extremely short and useful.