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Propsed length unit: angles as visual angle

From: Andrew n marshall <amarshal@usc.edu>
Date: Fri, 21 Nov 1997 09:09:37 -0800
Message-ID: <01BCF65F.28FC2330.amarshal@usc.edu>
To: "'www-style@w3.org'" <www-style@w3.org>

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?

Ideally this implies every display device should have knowledge about how 
it is viewed, and since it would be difficult to continuously update 
accurate measurements, it should only be assumed it is an average value. 
 While this isn't immediately available on most systems now, a good guess 
can be derived from the default font size for a device, making it not 
unreasonable to implement.

I am concerned that there is not a means to balance spatial frequency with 
device resolution.  It may be worth while implementing a means of defining 
this as "preferably _this_ visual angle, but not less than _this_ rendering 
resolution".  I think this is a valid point for discussion.

With this as a basis for all relative length values, authors can utilize 
existing perceptual psychology knowledge to help create pages that look 
good anywhere.

Andrew n marshall
  student - artist - programmer
      "Everyone a mentor,  Everyone a pupil"
Received on Friday, 21 November 1997 12:19:29 UTC

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