RE: [cgmo-webcgm] POLL ISSUE: zero-valued LINE WIDTH, stroke weight

[Dieter Weidenbrück <dieter@itedo.com>]

1a and 2a, then reopen the discussion for 2.1 (see Lofton's comments).

For the past 13 years I have had the question from customers why the CGM
world is not capable of changing the standard such that a simple thing
like a no-stroke line becomes possible.
NOTE: These are cases where no stroke is intentional.
The cases Forrest is referring to are probably degenerate cases, where
CGM writers relied on the recipient to handle degenerate cases well.



> -----Original Message-----
> From: Cruikshank, David W [mailto:david.w.cruikshank@boeing.com]
> Sent: Friday, June 10, 2005 10:18 PM
> To: CGM Open WebCGM TC
> Subject: [cgmo-webcgm] POLL ISSUE: zero-valued LINE WIDTH, stroke weight
> 
> 
> All,
> 
> I've read through the thread on this one and will summarize.
> 
> There are two questions here and everyone needs to answer them 
> independently.
> 
> 1)  What should WebCGM say about the treatment of zero width 
> lines (line width specifier of 0 value on the Line Width 
> attribute element in CGM)?
>    a)  Leave it as it is specified in WebCGM?
>    b)  Change the meaning of a zero value to mean "no stroke"?
> Recommendation a)
> 
> 2)  What should WebCGM say about the allowable values and 
> treatment of the stroke weight style property of WebCGM set 
> through the DOM?
>    a)  Limit value of both NVCC and relative scale to >0?
>    b)  Allow zero values for both NVDC and relative scale and 
> adopt CGM conventions?
>    c)  Allow zero values for both NVDC and relative scale and 
> define the meaning as "no stroke"?
> Recommendation a)
> 
> Summaries
> 
> 1)  The CGM standards allows for parameter values for the line 
> width specifier of the Line Width attribute element to be 
> non-negative.  That means the Line Width can be set to zero in 
> CGM.  In the "informative" guideline for interpreters in Annex D, 
> the CGM standard recommends: "If a zero size is specified in the 
> metafile, it is recommended that interpreters select the minimum 
> available size for affected primitives."  Currently in the WebCGM 
> 2.0 Profile (T20.3), the meaning of a zero value is "Minimum 
> available line width".
> 
> 2)  Currently the WebCGM 2.0 DOM chapter has a restriction of the 
> allowable values for stroke width.  It limits the relative scale 
> stroke width to >0%, but doesn't address absolute NVDC as far as 
> I can tell.
> 
> Personal thoughts
> 
> >From a user standpont we have had a requirement for a "line 
> visibility" element in CGM similar to Edge Visibility, but I 
> think that is something that should be addressed at the CGM 
> standard level and not in the profile.
> 
> thx...Dave Cruikshank
> 
> Technical Fellow - Graphics/Digital Data Interchange
> Boeing Commercial Airplane
> 206.544.8876, fax 206.544.9590
> david.w.cruikshank@boeing.com
> 
>