[GRASS-dev] any randomness in i.segment ?

[Moritz Lennert]

On 28/03/18 17:53, Markus Metz wrote:
> 
> 
> On Wed, Mar 28, 2018 at 3:04 PM, Moritz Lennert 
> <mlennert at club.worldonline.be <mailto:mlennert at club.worldonline.be>> wrote:
>  >
>  > Hi,
>  >
>  > Working with a colleague and comparing results we were wondering 
> whether i.segment contains any randomness effects which might make 
> results differ from one run to another.
> 
> There is no randomness in i.segments. Given he same input data and 
> settings, results should be identical between runs, i.e. repeatable.
> 
> Did you do a simple diff with r.mapcalc?

No, but we have variance and spatial autocorrelation values for the 
datasets and didn't get the same results. As there is no randomness, I 
suppose my colleague did not define the region the same way I did. 
Unfortunately, he only kept the numerical values, not the segmentation 
results.

>  >
>  > In the manual it says in section Seeds in the chapter on region growing:
>  >
>  > "The seeds map can be used to provide either seed pixels (random or 
> selected points from which to start the segmentation process) or seed 
> segments."
>  >
>  > which sounds as if the module creates random seeds if none are given. 
> Looking through the code, I do not find such creation of random seeds, 
> though. Is this just me not looking correctly, or aren't there any ?
> 
> A seed map can be created by randomly selecting pixels, e.g. with 
> r.random. If a seed map is not given, all non-NULL cells are seeds.
> 

Thanks for the info.

Moritz