location of images for PDF

I'm using the default for   
	
<format>pdf:<xsl:param>img.src.path

and this is OK for html but when I generate a PDF I get this warning (and no
pictures :-(  )

    (flow [flow-name xsl-region-body]
        [warning] Could not retrieve image from
'http://svn.boost.org/svn/boost/trunk/doc/html/../images/single_threaded.png':
java.io.IOException: HTTP response status is 404
        [warning] Could not retrieve image from
'http://svn.boost.org/svn/boost/trunk/doc/html/../images/4_threaded.png':
java.io.IOException: HTTP response status is 404
        [warning] Could not retrieve image from
'http://svn.boost.org/svn/boost/trunk/doc/html/../images/entropy.png':
java.io.IOException: HTTP response status is 404
        [warning] Could not retrieve image from
'http://svn.boost.org/svn/boost/trunk/doc/html/../images/bits_per_byte.png':
java.io.IOException: HTTP response status is 404

I presume I need to set 

<format>pdf:<xsl:param>img.src.path

to some value?

http://docbook.sourceforge.net/release/xsl/1.77.1/doc/html/img.src.path.html

path-constant images_location : ./doc ; # location of SVG and PNG images
referenced by Quickbook.

 <format>pdf:<xsl:param>img.src.path=$(images_location)/

works for me with my pictures at /doc/images/  (though I'm not quite sure I
understand why)

But is this

http://svn.boost.org/svn/boost/trunk/doc/html/../

default a leftover from SVN days?

Paul

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Paul A. Bristow
Prizet Farmhouse
Kendal UK LA8 8AB
+44 (0) 1539 561830