[GRASS-user] aspect claculations with integer and float rasters

[Carlos Grohmann]

Thanks Helena.

That might be an interesting information to add to r.slope.aspect man
page. I always had the impression that just by converting to float,
r.slope.aspect would work better and not produce the artifacts.

best

Carlos



On Mon, Sep 17, 2012 at 10:39 AM, Helena Mitasova <hmitaso at ncsu.edu> wrote:
> Carlos,
>
> If the original DEM data are integers, the artifact is probably already in the data and
>  you will get the artifacts in certain regions depending on topography - mostly if it is relatively flat
> - it is already in the data. You can check in nviz.
> Converting to float is not enough - you need to reinterpolate and depending on how bad it is even that may not help.
> If I have such problem I usually randomly sample the DEM and reinterpolate  (but I do it in projected coordinates, not lat long).
> It may be enough just to use r.resamp.interp with slightly different resolution.
>
> Helena
>
> Helena Mitasova
> Associate Professor
> Department of Marine, Earth, and Atmospheric Sciences
> 2800 Faucette Drive, Rm. 1125 Jordan Hall
> North Carolina State University
> Raleigh, NC 27695-8208
> hmitaso at ncsu.edu
>
> "All electronic mail messages in connection with State business which are sent to or received by this account are subject to the NC Public Records Law and may be disclosed to third parties.”
>
> On Sep 17, 2012, at 4:34 AM, Markus Neteler wrote:
>
>> Helena,
>>
>> do you have any pointers for Carlos?
>>
>> Thanks,
>> Markus
>>
>> On 9/17/12, Carlos Grohmann <carlos.grohmann at gmail.com> wrote:
>>> Hi all.
>>>
>>> I'm a bit annoyed by some aspect maps here. Using SRTM in a lat/long
>>> location, aspect presents the
>>> usual artifacts at 0, 45, 90, etc. So I tried to convert it to float, but
>>> using
>>> new = old * 1.0
>>> in mapcalc didn't worked (I can swear it worked before), so I used
>>> new = old + 0.00001
>>>
>>> and then I ran r.slope.aspect again, but my aspect raster still shows
>>> the artifacts.
>>>
>>> Does this have any thing to do with a lat/long location?
>>>
>>> I'm on OSX with Kyngchaos packages, btw.
>>>
>>> best
>>>
>>> Carlos
>>>
>>>
>>>
>>> --
>>> Prof. Carlos Henrique Grohmann
>>> Institute of Geosciences - Univ. of São Paulo, Brazil
>>> - Digital Terrain Analysis | GIS | Remote Sensing -
>>>
>>> http://carlosgrohmann.com
>>> ________________
>>> Can’t stop the signal.
>>> _______________________________________________
>>> grass-user mailing list
>>> grass-user at lists.osgeo.org
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>>>
>



-- 
Prof. Carlos Henrique Grohmann
Institute of Geosciences - Univ. of São Paulo, Brazil
- Digital Terrain Analysis | GIS | Remote Sensing -

http://carlosgrohmann.com
________________
Can’t stop the signal.