[GRASS-user] Re: Feature extraction in GRASS and Landserf.

[Marcello Gorini]

On Mon, Aug 16, 2010 at 10:20 PM, Marcello Gorini <gorini at gmail.com> wrote:
>>
>> Dear all,
>>
>> By comparing morphometric feature maps obtained from both "r.param.scale"
>> in
>> GRASS and the function "sufparam" using LandScript in Landserf (Wood,
>> 1996-2009), I noticed great discrepancies.
>>
>> Actually, a morphometric feature map derived in GRASS using slope
>> tolerance
>> of 3 and curvature tolerance of 0.000003 is similar (visually) to a map
>> derived in Landserf using 3 for slope and 0.05 for curvature.

>Markus:

>Please generate a difference map (color table "differences") and put a
>screenshot online somewhere. Perhaps also drawn over the shaded
>DEM (r.shaded.relief) with d.his (h=differences i=shaded_terrain).
>
>Markus

Dear Markus,

Sorry for my very late response, I was REALLY far away from the computer.

I attached the feature maps both from GRASS (the top one) and Landserf (the
bottom one). The DEM is a huge seamount and its surroundings, obtained from
the GEBCO grid (1000 meters grid size). As you can see, the discrepancies I
mentioned are so great that I believe no differences maps are needed (I
think you will agree with me, but if not I could gladly send you the dif
map).

Both maps use slope tolerance of 3 and curvature tolerance of 0.000003. 

In order to make these maps look the same, I had to use curvature tolerance
of 0.11 in Landserf, leaving the same slope value. I know the slope value is
in degrees both in GRASS and Landserf and I know the curvature value in
Landserf is dimensionless, but I don't know the unit of curvature in GRASS.  

I believe that both GRASS and Landserf use the same Wood's algorithm, so
there should not be any differences, right?

Or are there any modifications in the GRASS version? With respect to units,
maybe?

I thank you very much for any help.

Marcello.
http://osgeo-org.1803224.n2.nabble.com/file/n5460832/GRASS_features.png 
http://osgeo-org.1803224.n2.nabble.com/file/n5460832/LANDSERF_features.png 

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