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Propsed length unit: angles as visual angle

From: Hakon Lie <howcome@w3.org>
Date: Sat, 22 Nov 1997 01:01:19 +0100 (MET)
Message-Id: <199711220001.BAA21511@stovner.a.sol.no>
To: Andrew n marshall <amarshal@usc.edu>
Cc: "'www-style@w3.org'" <www-style@w3.org>
Andrew n marshall writes:

 > Style sheets do not have any length that correspond to how a page my be 
 > viewed.  The relative values that do exist relate to some preexisting 
 > absolute value.  For example, %, em, and ex correspond to the inherited 
 > font size.  The closest we have is px, which really does cut it when you 
 > try to describe how a page viewed on a large screen TV at 800x600 gets 
 > printed on a 600dpi printer.  But even that does really go to the extremes 
 > that I'm thinking of.  How does a page map from a projected screen (a 
 > presentation, a New York/Tokyo/London style marquee, or in place of those 
 > pre-movie slide shows you get at theaters) do to a more personal space of 
 > virtual/augmented reality glasses.  I realize that the this may not be the 
 > range of media you may have been thinking of, but is there any reason you 
 > shouldn't be?

No, style sheets that scale from one medium to the other are good, if
not always doable. 

I'm trying to follow your line of argument above, but there seems to
be a couple of "nots" missing? In any case, have you looked at how the
"px" unit is defined in CSS1 [1]:

  Pixel units, as used in the last rule, are relative to the resolution
  of the canvas, i.e. most often a computer display. If the pixel
  density of the output device is very different from that of a typical
  computer display, the UA should rescale pixel values. The suggested
  reference pixel is the visual angle of one pixel on a device with a
  pixel density of 90dpi and a distance from the reader of an arm's
  length. For a nominal arm's length of 28 inches, the visual angle is
  about 0.0227 degrees.

[1] http://www.w3.org/TR/REC-CSS1#length-units

Regards,

-h&kon

H      k   o   n      W   i   u   m       L   i   e
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Received on Friday, 21 November 1997 19:18:54 GMT

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