[mapserver-dev] SYMBOLTRANFORM for special symbols rendering

[Brent Fraser]

Alan,

I'm assuming this is mainly for Vector Field Rendering?  (I get a broken 
link for the graphic in the RFC)

Best Regards,
Brent Fraser


On 11/24/2011 9:25 AM, Alan Boudreault wrote:
> Hi devs,
>
> A while ago, it has been discussed about a new way to render a symbol, 
> which in this case is an arrow. The need is to be able to draw the 
> body arrow (a line) scaled depending of a value (ie, the magnitude in 
> vector field) but to not scale the arrow head.
>
> Mike, Daniel and Thomas discussed this problem in Denver during FOSS4G 
> and they came up with the concept of ARROWBODY and ARROWHEAD. Those 
> concepts  are essentially to determine what need to be scaled. 
> Following a discussion this morning.. here's the approach we would 
> like to use:
>
> * We define two symbols: the arrow body and the arrow head.
> * The arrow head symbol needs to have the ANCHORPOINT set to the head.
> * We define 2 styles: one for the body and the other for the head.
> * The two style would use a new option: SYMBOLTRANSFORM, which is to 
> draw the symbol correctly (scalable of not).
>
> Mapfile example:
>
> SYMBOL
>   NAME "arrowbody"
>   TYPE vector
>   FILLED true
>   POINTS
>      0 0
>      1 0
>   END
> END
>
> SYMBOL
>   NAME "arrowhead"
>   TYPE vector
>   FILLED true
>   ANCHORPOINT 0.25 0
>   POINTS
>      0 0.25
>      0.25 0
>      0 -0.25
>   END
> END
>
>
> # in the layer definition....
>
> STYLE
>    SYMBOLTRANSFORM arrowbody
>    WITDH 1
>    SIZE [uv_length]
>    ANGLE [uv_angle]
>  END
>  STYLE
>    SYMBOLTRANSFORM arrowhead
>    SYMBOL "arrowhead"
>    ANGLE [uv_angle]
>    OFFSET [uv_length] 0
>    SIZE 4
>  END
>
> In the arrowhead, we *NEED* to pass the length of the arrowbody (via 
> OFFSET), since it will be used to determine where the arrow head 
> should be positioned. the SYMBOLTRANSFORM arrowhead option would tell 
> the symbol renderer TO NOT scaled the symbol in length. In this 
> example, we use the terminology arrowbody/arrowhead.... but we are 
> going to use generic terms to use that feature in other cases.
>
> I'm glad to hear your comments and suggestions about that approach!
>
> Regards,
> Alan
> _______________________________________________
> mapserver-dev mailing list
> mapserver-dev at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/mapserver-dev
>