readimageblob: Fatal Error when converting SVG into PNG

Question

I'm trying to use Image-Magick with PHP to convert SVG text into a PNG image. This SVG is a chart generated with NVD3 and I'd like to allow my users to download it as an image.

Basically, I'm sending the SVG data, encoded with JSON to the PHP handler which is supposed to output it as a PNG image.

But, this throws up the following error:

Fatal error: Uncaught exception 'ImagickException' with message 'no decode delegate for this image format `' @ blob.c/BlobToImage/347' in svg2png.php:4 Stack trace: #0 svg2png.php(4): Imagick->readimageblob('

The PHP script for converting the image:

<?php
    /* Derived in part from: http://stackoverflow.com/a/4809562/937891 */
    $svg=json_decode($_REQUEST["svgData"]);
    $im=new Imagick();
    $im->readImageBlob($svg);
    $im->setImageFormat("png24");
    header("Content-Type: image/png");
    $thumbnail = $im->getImageBlob();
    echo $thumbnail;
?>

HTML:

<form id="exportSpendTrendTrigger" method="POST" action="svg2png.php" target="_blank">
    <input id="exportSpendTrendSvgData" type="hidden" name="svgData" />
    <input type="submit" class="btn" value="Export" />
</form>
<div id="spendtrend">
    <svg></svg>
</div>

jQuery:

exportSpendTrend = function (e) {
    //Show the user the PNG-image version for download
    $("#exportSpendTrendSvgData").val( JSON.stringify($("#spendtrend").html().trim()) );
}

$("#exportSpendTrendTrigger").on("submit", exportSpendTrend);

Example SVG, generated by NVD3: http://pastebin.com/Z3TvDK16

This is on an Ubuntu server with PHP 5.3 and Imagick

Answer 1

And remember that

<?xml version="1.0" encoding="UTF-8" standalone="no"?>

must be the first line in a variable that contains SVG text. Knowing that may save you some headaches.