[mapserver-dev] SYMBOLTRANFORM for special symbols rendering

[Alan Boudreault]

Mainly yes, but might be apply to any other cases. hmm.. I see the 
graphic properly in the rfc...

http://mapserver.org/trunk/development/rfc/ms-rfc-78.html

Alan

On 11-11-24 12:46 PM, Brent Fraser wrote:
> 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
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>>
>