[mapserver-users] How to display vector symbols (direction andmagnitude) in MapServer?

[Steve Lime]

Just in terms of the image...

Steve

>>> On 8/18/2008 at 6:30 AM, in message <48A95D5F.2070606 at nsidc.org>, John Maurer
<maurerj at nsidc.org> wrote:
> Thanks for the suggestion, Daniel! I was unaware of the ANGLE parameter 
> in MapServer 5.0. One remaining concern I have, though, is how the angle 
> will be interpreted by MapServer? Will -90 degrees always point to the 
> South Pole regardless of the map projection I'm using (e.g. a polar 
> stereo map centered on the South Pole), or will it always just point to 
> the bottom of the map image regardless of the projection? i.e. Does 
> MapServer interpret the degrees spatially or just in terms of the image? 
> Unfortunately, if the latter is the case (which I suspect it probably 
> is) it will not solve my problem. Do you know? Thanks again!
> Cheers,
> John Maurer
> 
> Daniel Morissette wrote:
>> John Maurer wrote:
>>> Dear MapServer Users,
>>> Does anybody have experience displaying vectors in MapServer? By 
>>> "vectors", I don't mean the usual vector vs. raster difference. What 
>>> I mean is displaying data like wind vectors, which are point 
>>> locations that have both a direction (degrees) and magnitude (e.g. 
>>> meters per second). Usually these are displayed as arrows, which each 
>>> point in a certain direction and whose tails vary in length depending 
>>> on the magnitude each measurement. Is this possible in MapServer? 
>>> Thanks for any suggestions!
>>
>> You could bind the symbol size and angle to an attribute in your layer 
>> definition.
>>
>> If you can precompute the size in pixels based on the wind speed and 
>> store that to an 'arrowsize' attribute then you could use a layer 
>> defn's like this:
>>
>> LAYER
>>   TYPE POINT
>>   ...
>>   CLASS
>>     SYMBOL 'arrow'
>>     ANGLE [direction]
>>     SIZE [arrowsize]
>>     COLOR 0 0 0
>>   END
>> END
>>
>>
>> If you can't precompute the arrow size in pixels, then you could use 
>> classes based on the wind speed attribute:
>>
>> LAYER
>>   TYPE POINT
>>   ...
>>   CLASSITEM 'windspeed'
>>   CLASS
>>     EXPRESSION ([windspeed] < 5)
>>     SYMBOL 'arrow'
>>     ANGLE [direction]
>>     SIZE 10
>>     COLOR 0 0 0
>>   END
>>   CLASS
>>     EXPRESSION ([windspeed] < 25)
>>     SYMBOL 'arrow'
>>     ANGLE [direction]
>>     SIZE 15
>>     COLOR 0 0 0
>>   END
>>   CLASS
>>     EXPRESSION ([windspeed] < 100)
>>     SYMBOL 'arrow'
>>     ANGLE [direction]
>>     SIZE 20
>>     COLOR 0 0 0
>>   END
>>   CLASS
>>     # No expression ... catch all for windspeed > 100
>>     SYMBOL 'arrow'
>>     ANGLE [direction]
>>     SIZE 25
>>     COLOR 0 0 0
>>   END
>> END
>>
>>
>> Daniel