W3C home > Mailing lists > Public > www-svg@w3.org > June 2001

Re: question on spec

From: Jon Ferraiolo <jferraio@Adobe.COM>
Date: Tue, 26 Jun 2001 16:00:52 -0700
Message-Id: <4.3.2.7.2.20010626154827.00d8ef00@mailsj>
To: Wendell Piez <wapiez@mulberrytech.com>
Cc: www-svg@w3.org
Wendell,

There will be some clarifications in the Proposed Recommendation of the SVG 
specification in this area. Some clarifications have already been done (by 
not yet made public), but based on your comments below, I think additional 
minor cleanup would help reduce confusion.

There are really two situations for "px" units:

1) On the outermost 'svg' element, you can define the instrinsic 
width/height of the graphic in "px" units. In this use case, a "px" is 
generally an system-dependent unit of measure. On many systems, a "px" will 
map to one device pixel, and different devices have different resolutions, 
so "px" might cause different sizes rendering on different systems. Also, 
on very high-res monitors or on printers, a "px" might be an abstract 
measurement typically in the range of 1/72 to 1/120 inch, again possibly 
causes different rendering sizes on different systems.

This case is the reason for the words: "...use of px units ... can cause 
inconsistent visual results on different viewing environments since the 
size of '1px' may map to a different number of user units on different 
systems..." But now that you bring this up, I think some additional 
rewording may be warranted.

2) Otherwise, "A px unit and a user unit are defined to be equivalent in SVG."

Jon Ferraiolo
SVG Editor
jferraio@adobe.com

At 03:59 PM 6/26/01 +0100, Wendell Piez wrote:
>Hi,
>
>How do I reconcile the statement in the SVG CR, section 7.10, "Units":
>
>"A px unit and a user unit are defined to be equivalent in SVG."
>
>with the statement, below it, that
>
>"...use of px units ... can cause inconsistent visual results on different 
>viewing environments since the size of '1px' may map to a different number 
>of user units on different systems..."
>
>Is a 'user unit' a px, or ain't it? what am I missing?
>
>Thanks,
>Wendell
>
>
>
>======================================================================
>Wendell Piez                            mailto:wapiez@mulberrytech.com
>Mulberry Technologies, Inc.                http://www.mulberrytech.com
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Received on Tuesday, 26 June 2001 19:01:42 GMT

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