[mapserver-users] Re: Mapserver + NDVI styling

[Steve Lime]

Unfortunately MapServer isn't bright enough to generate a legend
solely from an image itself. The legend code
just wasn't built for such a task.Sorry... Steve

2011/9/28 Jorge Arévalo <jorge.arevalo at deimos-space.com>:
> 2011/9/28 Jorge Arévalo <jorge.arevalo at deimos-space.com>:
>> I'm serving a NDVI coverage via Mapserver. So, one band, float32
>> values, [-1.0, 1.0]. I want to display the NDVI in greyscale, and
>> generate a legend. I've tried 2 things:
>>
>> - Create two dummy classes, just for testing:
>>
>> CLASS
>>    NAME "rojo"
>>    EXPRESSION ([pixel] < 0.3)
>>    STYLE
>>        COLOR 255 0 0
>>    END
>> END
>>
>> CLASS
>>    NAME "azul"
>>    EXPRESSION ([pixel] >= 0.3)
>>    STYLE
>>        COLOR 0 0 255
>>    END
>> END
>>
>> So, my legend looks like this: http://dl.dropbox.com/u/6599273/leyenda.png
>>
>> And the image, obviously, is red and blue:
>> http://dl.dropbox.com/u/6599273/capturas/ndvi_en_gvsig.png
>>
>> But I'd like to see the image in greyscale... The I've tried the next thing
>>
>> - Pre-classify values with PROCESSING "SCALE=-1.0, 1.0". I don't know
>> what Mapserver internally does with this processing order, but I can
>> see the image in greyscale:
>> http://dl.dropbox.com/u/6599273/capturas/ndvi_gris_en_gvsig.png
>>
>> The problem is now I can't see any legend, because I've not created
>> any class. I'd like to see all the different levels of the grayscale
>> image in my legend.
>>
>> How could I do it?
>>
>> Many thanks in advance
>>
>> --
>> Jorge Arévalo
>> Internet & Mobility Division, DEIMOS
>> jorge.arevalo at deimos-space.com
>> http://es.linkedin.com/in/jorgearevalo80
>> http://mobility.grupodeimos.com/
>> http://gis4free.wordpress.com
>> http://geohash.org/ezjqgrgzz0g
>>
>
> Ok, I've found a way, but I'm sure it isn't the shortest path.
>
> Basically, I've generated a legend using GRASS (r.colors to add grey
> color as color interpretation for band and d.legend to generate the
> legend). The legend is generated from the ndvi file. So, I guess I can
> create a HTML template as Mapserver legend, using the legend generated
> by grass (here:
> http://dl.dropbox.com/u/6599273/grass/grass_legend.png)
>
> On the other hand, I know how to generate a legend in Mapserver using
> CLASS objects in the mapfile, but I don't know how to generate that
> legend without the CLASS options in the mapfile.
>
> Am I taking the long way on this? Is there an easier way to generate a
> legend for a NDVI file in Mapserver?
>
> Many thanks in advance
>
> --
> Jorge Arévalo
> Internet & Mobility Division, DEIMOS
> jorge.arevalo at deimos-space.com
> http://es.linkedin.com/in/jorgearevalo80
> http://mobility.grupodeimos.com/
> http://gis4free.wordpress.com
> http://geohash.org/ezjqgrgzz0g
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