[Docutils-users] image directive and units of measure

[Joachim Koenig-B. <jo...@cm...>]

Hi,

I'm using docutils in conjunction with the xsl stylesheet for docutils-xml
to docbook-xml conversion posted by Eric Bellot some days ago and have a
question concerning image height and width.

The docutils directive document states that :height: and :width: are number
interpreted as pixels:

> height : integer
>     The height of the image in pixels, used to reserve space or scale
>     the image vertically.
> width : integer
>     The width of the image in pixels, used to reserve space or scale
>     the image horizontally.

docbook allows to specify units of measure as in TDG:

> Units of Measure
> 
> The size of the viewport area and the content area are defined in terms
> of lengths (width and depth).
> 
> Lengths must be expressed as a decimal value followed immediately by an
> optional unit of measure or a percentage. Six and one eight inches, for
> example, must be expressed as 6.125in. It is an error to put a space or
> other punctuation between the decimal value and the unit of measure.
> 
> The following units of measure may be used:
> pt Points (1/72 of an inch)
> cm Centimeters
> mm Millimeters
> in Inches
> pc Picas (1/6 of an inch)
> px Pixels
> em Ems
> 
> If no unit of measure is provided, px is assumed. Note that pixels have
> no universally accepted absolute size and ems are relative units of
> measure. Implementations may define pixel sizes differently and
> stylesheets may or may not be able to determine the current font size
> in order to correctly calculate the absolute size of an em. It is best
> to avoid these units of measure.
> 
> Percetages are expressed as a decimal value followed immediately by a % sign.

So I wonder why there is a fixed interpretation in docutils for these
measures. E.g. for the inclusion of an SVG image into pdf the interpretation
of pixels is not easy as pointed out in TDG and I would like to be able to
specify the units of measure as applicable. Could the DTD be adjusted for
that? The concrete interpretation could be left to the transformations.

Joachim