Re: [Geotools-devel] SLD graphicstroke gaps

[Graham D. <gd...@re...>]

Thanks Andrea, that all makes sense.  Currently we are in the research 
phase to try and determine various ways we could accomplish our desired 
result.  This was one possible way, but it does seem unsatisfactory.  I 
now understand the problem of the different ways and uses that could be 
used to draw symbols at end points, and that is useful.  If our client 
decides to go the SLD route, we might be able to help you with this SLD 
change, or even do it for you.  I appreciate the response, thanks.

Graham.


Andrea Aime wrote:
> Graham Davis ha scritto:
>> This may not be the best place to ask this question, but I'm trying 
>> to do something with SLD in uDig which I believe uses GeoTools for 
>> SLD stuff.
>>
>> I'm looking at ways to display multiple routes that overlap so that 
>> each route is visible side-by-side.  One idea was to use SLD to style 
>> the lines with images that have transparent offsets in them.  For 
>> instance, line 1 would be red and be drawn as normal, line 2 would be 
>> green and would have 2 transparent pixels above the green part the 
>> line graphic (so that the red line still appeared and so the green 
>> line appeared displaced by 2 pixels).  I have this idea working 
>> somewhat in my examples, however, I am not satisfied with how the 
>> graphicstroke draws graphics along a line.  There are gaps/spaces at 
>> every vertex. I've tried searching for various cssparameters and 
>> other rules to prevent this, but nothing seems to work.  No matter 
>> what I do, there are always gaps.  Here is an example linesymbolizer 
>> from my SLD.  
>
> You don't say which version of GeoTools you're using.
> Anyways, I've been playing with this topic a bit in my spare time some
> months ago and I could not find any satisfactory solution.
> The renderer is playing blind here, it has a square/rectangular
> block that has to be painted along a line and when a corner is reached
> there are various policies that can be taken:
> - stop at the last full image that can be drawn along the line
> - have the image be full drawn even if it extends past the end
>   of the line
> - cut the image and reach the end of the block
> - keep on following the line and just find a point that's far enough
>   from the last one reached to draw a full image block, forgetting
>   about the corner itself
>
> Basically each policy works in some cases but not in others. In
> your case you are trying to fake a continuous line so approach
> 3 seems to be the one that works best, but other times you're
> trying to depict a line with circles or other symbols that you
> don't want to get partially drawn or superimposed at corners,
> so approach 1 or 4 work better.
>
> This would need to be handled using some vendor parameter controlling
> how the graphics is being stroked along the line, which is doable,
> and I would like to implement before FOSS4G 2009. Maybe I'll tackle
> this problem during summer vacations.
>
>>  Also, I notice various email threads and forum postings about maybe 
>> having a displacement/offset attribute added for lines.  Is this 
>> already part of the 1.1.0 SLD spec, or something new?  Does GeoTools 
>> implement 1.0.0 or 1.1.0 of the SLD spec?
>
> StreamingRenderer/ShapefileRenderer implements version 1.0.0 of the
> spec. Implementing v1.1.0 is beyond reach for a weekend project, it
> would take quite some time and thus needs some sponsoring.
>
> Cheers
> Andrea


-- 
Graham Davis
Refractions Research Inc.
gd...@re...