[GRASS-user] EVI algorithm

[Markus Neteler]

(please do "reply-all")

On Fri, Jul 13, 2012 at 10:09 AM, Danut Mihon <danut_mihon at yahoo.com> wrote:
> Hi,
>
> I am not aware of scaling the images before importing them into GRASS. The
> range for all three inputs in [0, 255].

Where do the maps come from?

> The EVI result is between [-1, 1],
> but here comes the strange part:
> - the areas with rich vegetation have values close to -1
> - the urban areas correspond to higher values (e.g. 0.2)

In fact, unusual and like "reverted".

> It should be the other way around. One solution is to multiply all values
> with -1, but I do not think that this is a general solution. Maybe you have
> some better ideas to guide to.

It does not make much sense because NDVI/EVI do not need any reverting.

> Maybe these seem "silly" questions to you, be I am a novice in GRASS.

Not silly at all. I suspect an input data problem but would need to see
one of these input maps (I worked successfully with MODIS EVI in GRASS).

Markus