Beginning Google Maps Applications

In the last few weeks we’ve seen an explosion of people complaining about the lack of asinh() on the Windows version of PHP. We use the asinh() function extensively in Chapter 7 for the custom tile overlays. Admittedly, we didn’t test any of the code against windows versions of PHP (we’re LAMP folks), so until the middle of September when Stuart contacted us to ask a question we had no idea about the problem.

So far the solution isn’t great. User comments from the PHP.net documentation suggest:

if (!function_exists("asinh")) {
  function asinh($z) {
    return log($z + sqrt($z^2 +1));
  }
}

However, due to limitations in float-point computation, the accuracy of this alternative function breaks down at higher zoom levels, especially close to the equator. At least two alternatives exist. Our reader Stuart suggests an arbitrary fudge factor of 1.65:

if (!function_exists("asinh")) {
  function asinh($z) {
    return log($z + sqrt(($z^2) + 1 ),  1.65);
  }
}

Another reader of our book, Allan, posted a comment at PHP.net suggests using ln rather than log:

if (!function_exists("asinh")) {
  function asinh($x)
  {
    return ln($x + sqrt(1 + pow($x, 2)));
  }

  function ln($x)
  {
    return $x = log($x)/log(M_E);
  }
}

We haven’t got a Windows box to test these out on, but here’s what they look like on Linux. Anyone got a suggestion for us?

Aside that isn’t worth it’s own post…

There have been lots of developments in the GoogleMaps world, hopefully you’ve been following the official Google Maps API Blog for news like that. The books continue to get rave reviews and both are still excellent primers for digging into the world of maps. Very little of the code in the books is wrong or obsolete even after more than a year on the shelves. For a technology book we’re pretty proud about that. Sure, there are new functions in the API that handle some of the work for you that didn’t exist when we wrote the book, but our methods work just as well and often take some of the burden off of the user’s browser… If you agree, please consider writing a review on Amazon.com for us. Thanks in advance!