[mapserver-users] Re: Mapserver + NDVI styling

[Jorge Arévalo]

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