Monday, November 16, 2009

Update: Drivers with hemianopia do worse in driving simulator

A group of Harvard researchers published a report that persons with hemianopia performed worse in a diving simulator than normally sighted persons.

Specifically, the persons with hemianopia had difficulty detecting pedestrians on their blind side. This is often the stated concern about letting persons with hemianopia drive - they will have trouble seeing traffic and pedestrians on their blind side.

In contrast, the study published in February 2009 was a "real world" test, where persons were actually taken out on the road in a using a dual-brake vehicle and monitored by a certified driving rehabilitation specialist.

The two studies are not directly comparable, in that the methodologies are strikingly different. However, we can attempt to make reconcile the apparently conflicting results.

The new study states that drivers with hemianopia are not as good as normally-sighted drivers. The real-world study says that they are good enough.

Monday, November 02, 2009

PHP class adds SVG images to PDF files

I have modified the svg2pdf PHP class from Sylvain Briand at for incorporating SVG graphics into a PDF document. The original class is an extension of the awesome FPDF class for creating PDF documents on the fly using PHP. Because FPDF does not support SVG graphics, there is a need for this extension. Briand's class works great, but did not meet all of my needs. My modification adds the following capabilities:

1. Write text on an SVG graphic
2. Transform scale support
3. Overflow hidden support (incomplete)
4. Place multiple SVG graphics on a single page
5. Produce a multi-page PDF document


Within the SVG standard, this would correspond to using a text element, as below:

<text x="210" y="15" font-family=”times” font-weight=”bold” font-style=”italic” font-size="10" fill="red">Hello World</text>

The PDF standard defines 3 standard fonts that all readers should support (Helvetica, Times, and Courier). You can use these fonts, with their bold and italic variants, without issue. The parent FPDF class supports external font definition files, so if you want to use any other font you must import it before calling ImageSVG() [not tested, see FPDF docs for more information on importing fonts].

There is no support for manipulating orientation, baseline alignment, directionality, etc.


Within the SVG standard, this would correspond to using a transform attribute as below:

<g transform="scale(scale_x,scale_y)">

The original class only supported applying styles with the g element. The modified class adds support for scale transformations.

Other transformations (rotate, skew, etc) are not supported.


It is possible, using the drawing tool that generates my SVG graphics, for graphical elements to extend beyond the borders of the image. Therefore, I needed a way to crop these elements down to the height and width defined for the image. Within the SVG standard, this would correspond to applying the overflow attribute of the svg element as below:

<svg overflow="hidden">

Sorry, but I was only able to implement cropping for path objects. Rendered objects (circles, rectangles, etc) may still extend beyond the borders defined for the image.


It is now possible to call ImageSVG() multiple times for a single PDF document, and to add SVG graphics to multiple pages of a multi-page PDF file.

You can download the modified svg2pdf class here. I hope you find it helpful.