Online raster processing?

[Frank Warmerdam]

Teemu Makela wrote:
> In MapServer Documentation "Raster Data Access" is a following example:
> 
> "CLASS
>     NAME "near white"
>     EXPRESSION ([red] > 200 AND [green] > 200 AND [blue] > 200)
>     STYLE
>       COLOR 0 255 0
>     END
> END"
> 
> However, it is also stated that "Raster classifications always take place on
> only one raster band. It defaults to the first band in the referenced file,
> but this can be altered with the BANDS PROCESSING directive."
> 
> IS IT POSSIBLE TO CLASSIFY SEVERAL BANDS?

Teemu,

No, it is not currently possible to classify several bands.
The above "near white" example only works meaningfully for
one band files with a color table.  In which case it will
select all pixels who's color table entries are near white.

Internally raster classification in Mapserver works by classifying
in a lookup table, and this precludes multi-band operations.  In any
event, the expression lookup approach in mapserver is slow enough that
I would not want to try it for each pixel which is what would be
required for real multi-band classification.

Sorry!

Best regards,
-- 
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