Re: Chemical Engineering package

[Lars Clausen <lrclause cs uiuc edu>]

On 26 Jun 2003, Federico Zenith wrote:
> Hi all,
> I developed a collection of Dia shapes useful in drawing
> chemical-engineering process-flow diagrams. Here they are:
> http://www.nt.ntnu.no/~zenith/dia/dia.html
> 
> I already used the package for some real work, i. e. a few redrawings of
> process flow diagrams for my academic tutor's second edition of his book
> prosessteknikk (in Norwegian), and in minor extent to draw a detailed
> scheme of a sieve-tray distillation column for a student lab I'll be an
> assistant for.
> 
> I developed the package either at home or overtime at work, so any IP
> claims from the university are not feasible. Anyway this place is the
> last in the world where they would make such claims, so no problem.

Great!  I'm sure they'll be useful.  Alan, can you take a look at them?

> Some comments about my experience:
> 
> The .shape export is a bit strange. All elements tend to get a
> style="fill: none; stroke-width: 0.1; stroke: #000000": I had to change
> them all manually to "fill: default", which would allow the user to
> change the figure's colour. While having more than one colour definable
> in a single picture would be nice, I understand that it implies much
> more work.
> Anyway, what about dispensing with that 0.1-stroke stuff? The
> modification would be much simpler and that would make production of new
> figures easier for beginners.

That's the problem with exporting shapes from Dia:  There's no way to mark
a line to be 'default', i.e. picked from the toolbox at creation time,
rather than specific.

> I noticed that when I tell the program to draw a figure with 0 line
> thickness, it draws it with 0.01. I must admit I do not know whether the
> issue has been debated before, so don't flame me please...:-) But
> figures with no borders are indeed useful and I used them plenty of
> times in .shape files (where I had to insert style="fill:default;
> stroke:none").

Thickness 0 used to be just a hairline, but it was pointed out that using
device-specific hairlines is a really bad idea for high resolution
printers, so we changed it to very small.  It's important to have n easy
way to make a 'very thin' line, but have no border on fillable objects is
of course also useful.

> About dotted/dashed lines et similia: what about implementing the
> possibility of a dotting/dashing pattern related to the actual size of
> the object, to improve scalability? A 1 meter long line with 1 mm dashes
> is one thing, but when it scales down to 1 cm the visual effect is
> definitely different.
> 
> Maybe it should be possible for the user to choose
> either "x mm" (or inches, feet, middle fingers or whatever insane unit
> the Americans use :-)

We would love to have changeable units in general, if anyone feels like
adding something.  Then we could set the stippling in appropriate units.

> or a given fraction of the line length, say x/100
> line length for instance.

That'd mean that two lines with the same stippling setting but of different
lengths would have different length stipples.  That'd look silly, and be
very difficult to calculate for, say, beziers.  Better to have a more
reasonable way to set dash length.

-Lars

-- 
Lars Clausen (http://shasta.cs.uiuc.edu/~lrclause)| HĂ„rdgrim of Numenor
"I do not agree with a word that you say, but I   |----------------------------
will defend to the death your right to say it."   | Where are we going, and
    --Evelyn Beatrice Hall paraphrasing Voltaire  | what's with the handbasket?