Hi mistercase,

> I need to build a map system for a GIS with some elements' size independent
> by the zoom level applied.

Humm... This sounds like another 'déjà vu' from a similar, recent
thread [1]. ;-)  (Weirdly, the message didn't seem to show up in
Nabble, so I'm not sure if that was why it was issued again.) Note
that mailing list messages can get lost sometimes so feel free to
"ping" after a while just to make sure that it wasn't the case, but
please try to do it within the same thread whenever possible. In this
particular case, for example, I still had the previous one in my list
for processing whenever possible (time is a finite resource,
unfortunately!).


> I've found a lot of questions about this issue but nobody looks like to have
> an idea on what to do [...]

Well, I wouldn't put things that way. There's at least a related
thread [2] and, given that it was found in a few seconds, I'm
convinced the proper keywords will find a lot more. Also, I recall
somehow recent (deep!) debates on affine transforms, which would be
pretty useful for getting this sort of effects! ;-)


> Such zoom-invariant elements are for example the stroke size of the streets,
> the size of text, some drawings size (like the car accident), ecc.. I
> understand it's a large problem.

In terms of invariable stroke width, SVG Tiny 1.2 specifically defines
that in the "non-scaling-stroke" value for the "vector-effect"
property [3]. Unfortunately, as far as I know, Batik doesn't implement
this yet (anyone feels like contributing this simple and yet
interesting/valuable feature?).


> ..and then applying it the inverse CTM of the root node. But this even
> doesn't work, because the transformation gives back an element which doesn't
> fit on the previous Bounding Box.

Well, I'm convinced an approach like this will work. Samuel Dagan's
Zoom and Pan [4] proof-of-concept employs this in a scripted
environment. By using Batik's infrastructure performance will
certainly improve. The sample makes the control element the same size
relative to document size; if one would want that but relative to an
absolute size, just needs to apply a similar transform during the
document load event. ;-)


> Waiting for an answer of yours [...]

Hope this helps,
 Helder


[1] 
http://mail-archives.apache.org/mod_mbox/xmlgraphics-batik-users/200904.mbox/%[email protected]%3e
[2] http://www.nabble.com/Custom-Scaling-tt13513744.html
[3] http://www.w3.org/TR/SVGTiny12/painting.html#VectorEffectProperty
[4] http://alzt.tau.ac.il/~dagan/tools/#zoom

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