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RE: More on getObjectExtent()

From: Lofton Henderson <lofton@rockynet.com>
Date: Mon, 01 Dec 2008 15:30:36 -0700
Message-Id: <>
To: "WebCGM WG" <public-webcgm-wg@w3.org>
At 09:49 AM 12/1/2008 -0500, Bezaire, Benoit wrote:
>Hi Dieter,
>I think most of them (except rasters) have been addressed.

Please clarify what might be missing here.  Per my previous message, I did 
a quick read about Cell Array and Tile Array in CGM:1999.  It seems clear 
what is the extent (ignoring transparency/visibility controls for the 
moment).  But maybe I'm missing something -- after all, I haven't tried to 
implement gOE().

>However, I do not think the group agreed to treat text as path.

Just to be sure I'm understanding -- what exactly does "treat text as path" 
mean?  Does it mean the minimal containing box of all the strokes/areas 
that are used to actually render the string?

The 2nd paragraph of the gOE description in 5.7.6 seems pretty definitive, 
though maybe different from "treat text as path".  It also seems like a lot 
cheaper computation.  So two questions:

1.) does the present 5.7.6 gOE approach have some fundamental problem that 
makes it unsuitable?
2.) if that present approach is suitable, then:  are there some holes or 
defects in the particular details as they are written?


>From: public-webcgm-wg-request@w3.org 
>[mailto:public-webcgm-wg-request@w3.org] On Behalf Of Weidenbrueck, Dieter
>Sent: Sunday, November 30, 2008 12:50 PM
>To: Lofton Henderson; WebCGM WG
>Subject: RE: More on getObjectExtent()
>good start. Do we need to add something about
>- raster images
>- text (should be treated as paths)
>- visibility/transparency (do they have an impact or not)
>- transformations (they do have an impact)
>From: public-webcgm-wg-request@w3.org 
>[mailto:public-webcgm-wg-request@w3.org] On Behalf Of Lofton Henderson
>Sent: Sonntag, 30. November 2008 17:26
>To: WebCGM WG
>Subject: Re: More on getObjectExtent()
>Since not everyone is satisfied with the simple fix of "s/abstract 
>locus/locus/" in 5.7.6, I'll make a proposal to close the "locus" 
>issue:  delete the word "abstract" and link "locus" to a glossary entry.
>Here is a first draft proposal:
>locus --
>The Oxford dictionary defines locus as:  "Curve formed by all points 
>satisfying particular equation of relation between coordinates, or by 
>point, line, or surface, moving according to mathematically defined 
>conditions."  In the WebCGM specification, locus refers to the set of 
>points that comprise the path or shape of a Graphical Primitive element, 
>or in the appropriate context, the combined shapes or paths collectively 
>of all of the Graphical Primitive elements in an Application Structure 
>(APS).  I.e., the locus of an APS comprises the combined loci of all of 
>the graphical primitives in the APS.  Locus does not include defining data 
>that are not part of the shape or path of the graphical primitive, such as 
>control points of Bezier primitives, or the center point of a Circular Arc 
>Center primitive.
>Question 1:  Are people okay with the solution of adding a definition to 
>the Glossary?
>Question 2:  Suggestions for improvement of the definition?
>At 09:45 AM 11/19/2008 -0700, Lofton Henderson wrote:
>>At 08:32 AM 11/19/2008 -0800, David Cruikshank wrote:
>>>I would agree with dropping "abstract".  Locus is a perfectly valid term 
>>>to define the path of the primitive.
>>>Probably ought to capture it somewhere to document the decision.
>>Just to clarify that last sentence -- you mean that you support the issue 
>>processing proposal to roll it into Issue3 in the DoC (see URI below)?
>>>On Wed, Nov 19, 2008 at 8:04 AM, Lofton Henderson 
>>><<mailto:lofton@rockynet.com>lofton@rockynet.com> wrote:
>>>>At 09:26 AM 11/19/2008 -0500, Bezaire, Benoit wrote:
>>>>>I think the wording should be revised.
>>>>Fair enough.
>>>>>Even Google doesn't come up with anything meaning full for "Abstract 
>>>>However, it does give lots of hits for a search like "definition of 
>>>>mathematical locus".  And we use "locus" repeatedly, in the proper 
>>>>sense, in the profile (Ch.6) -- i.e., "locus" is a pretty common term 
>>>>in  and has been used in WebCGM, for example, since 1999.  So it is my 
>>>>hastily-invented modifier "abstract" that is problematic.
>>>>Actually, I think a good solution would be to drop the word 
>>>>"abstract".  The next sentence after its occurrence fully explains what 
>>>>"abstract" was meant to convey.  (And we have agreed to clarify that sentence.)
>>>>(See the getObjectExtent definition in 5.7.6:
>>>>(Shall I just add this to fix to the clarification in DoC #3:
>>>>>From: Lofton Henderson 
>>>>>Sent: Tuesday, November 18, 2008 6:52 PM
>>>>>To: Bezaire, Benoit; WebCGM WG
>>>>>Subject: Re: More on getObjectExtent()
>>>>>At 01:52 PM 11/18/2008 -0500, Bezaire, Benoit wrote:
>>>>>>The wording says "[...] The bounding box calculation is based on the 
>>>>>>abstract locus of the primitives within the APS."
>>>>>>What does 'abstract locus' mean?
>>>>>The locus is the set of points comprising the drawn primitive (it's a 
>>>>>term I dredged up from my memory of some old math courses -- I hope I 
>>>>>got it right).  "Abstract locus" means that things like line width are 
>>>>>not included, but rather only the point positions as if the item were 
>>>>>drawn with an abstract, infinitely fine pen.
>>>>>>I'd like to know if getObjectExtent() returns a tight bounding box on 
>>>>>>a given APS. i.e., given a polybezier, are control points part of the 
>>>>>>bounding box calculations or not?
>>>>>No.  The control points are part of the defining data, but not part of 
>>>>>the drawn primitive.
Received on Monday, 1 December 2008 22:31:31 UTC

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