[mapserver-dev] SYMBOLTRANFORM for special symbols rendering

[Brent Fraser]

Ah.  If required, it could be something like

SYMBOLTRANSFORMORDER TSR   # (translate, then scale, then rotate)

but hopefully it won't be necessary...

Best Regards,
Brent Fraser


On 11/28/2011 12:01 PM, Alan Boudreault wrote:
> Hi Brent,
>
> I understand your point. I realize that SYMBOLTRANSFORM *could* be 
> removed for this feature. I haven't checked the code, but it depends 
> on how mapserver renders the symbol. The order of the rendering 
> (rotation and offset) is important to have the expected result:
>
> - if mapserver applies the offset BEFORE the rotation, you are right, 
> we do not need SYMBOTRANSFORM anymore. The two symbols will be 
> rendered the way we expect.
>
> - if mapserver applies the offset AFTER the rotation, the symbols 
> won't be rendered the way we expect since the the offset will be 
> applied differently. That why SYMBOLTRANSFORM would be used (we should 
> find a best keyword/option name). We need to a way to tell mapserver 
> to inverse the mechanism: to apply the offset *before* the rotation.
>
> regards,
> Alan
>
> On 11-11-28 11:19 AM, Brent Fraser wrote:
>> Alan,
>>
>> My imagining of how Vector field Rendering would work is that as the
>> user zooms in and out the symbols would remain more or less the same
>> size (except for any change due to a resampling of the grid values). It
>> would behave like GIS symbology (e.g. size in pixels), not CAD symbology
>> (size in meters), although I guess if SYMBOLSCALEDENOM were used you
>> could get symbol size based on scale.
>>
>> So my question is why the need for SYMBOLTRANSFORM? In your case, you
>> want the length of the line to vary with the grid value, but not the
>> width (I might want the width of the arrowhead to vary as well; I hadn't
>> thought about it):
>>
>> STYLE
>> SYMBOL "arrowbody" # the symbol name (a short line segment)
>> WIDTH 1 # constant "thickness" (according to doc)
>> SIZE [uv_length] # "height" of symbol; line length for this symbol
>> ANGLE [uv_angle] # angle of the arrowbody
>> END
>>
>> and only the position (not the width or the length) of the arrowhead
>> changes to match the length of the arrowbody symbol:
>>
>> STYLE
>> SYMBOLTRANSFORM arrowhead # why is this required?
>> SYMBOL "arrowhead" # a ">" symbol
>> ANGLE [uv_angle] # same angle as arrowbody
>> OFFSET [uv_length] 0 # ">" point is at the end of the arrowbody
>> SIZE 4 # constant height (width?) of ">"
>> END
>>
>> What am I missing?
>>
>> And I ran across
>> http://matplotlib.github.com/basemap/users/examples.html Have a look
>> near the bottom of the page for sample graphics of wind vectors and 
>> barbs.
>>
>> Best Regards,
>> Brent Fraser
>>
>>
>> On 11/24/2011 11:57 AM, Alan Boudreault wrote:
>>> 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
>>>>> _______________________________________________
>>>>> mapserver-dev mailing list
>>>>> mapserver-dev at lists.osgeo.org
>>>>> http://lists.osgeo.org/mailman/listinfo/mapserver-dev
>>>>>
>>>>
>>>
>>>
>>
>
>