[GRASS-user] Question to the input seed grid of i.segment

[Rashad Kanavath]

On Wed, Jan 25, 2017 at 11:22 AM, Moritz Lennert <
mlennert at club.worldonline.be> wrote:

> On 24/01/17 20:40, Raphael Knevels wrote:
>
>> Thanks for the quick response :-)
>>
>> The extent of my region is also the extent of my imagery-group. For
>> i.segment I used as memory 10240 MB with a threshold of 0.25.
>>
>
> That's a pretty large threshold which generally leads to
> under-segmentation. You might want to start with a value closer to 0.01.
>
>
>> In SAGA I used at first Seed Generation (Band Width of 18, but I
>> also
>> varied this parameter) for producing the Seed Output. The Seed Output is
>> a raster with floating point values. Moreover, the Seed Output contains
>> single pixels distributed over the hole area. The "space" between those
>> pixels is "no data". The segmentation is then computed by Seeded Region
>> Growing with the seed grid as input.
>>
>> "Seeds in i.segment have to be polygons not points. These polygons
>> are
>> represented by identical positive integer values (= IDs) in adjacent
>> pixels, and they have to cover the entire region. When used as seeds for
>> a segmentation, these polygons are the further merged."
>>
>
> Sorry, but this was actually wrong information from my part: i.segment
> also supports seed pixels. From the man page:
>
> "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. If the seeds are the results of a previous segmentation with
> lower threshold, hierarchical segmentation can be performed. The different
> approaches are automatically detected by the program: any pixels that have
> identical seed values and are contiguous will be assigned a unique segment
> ID. "
>
>
> However, the seed map has to have integer values. To get that from you
> SAGA output (floating-point) seed map, just run r.clump.
>
> -> alright. That means, I definitely must convert the no data values in
>> the SAGA Seed Output to zero or any other integer number.
>>
>
> No, I actually don't think this would help in any way as this would create
> one big region out of all the no data pixels...
>
> Meanwhile, I also tried the segmentation result of SAGA Seeded Region
>> Growing as Seeds for GRASS - this works...
>>
>
> And how long did this take ?
>
> " You could try using the brand new i.superpixels.slic add-on to create
>> superpixels which you can then use as seeds."
>> -> I could successfully install and open it ("g.extension
>> i.superpixels.slic", GRASS 7.2.0).
>> However, when I run the tool with default settings, GRASS gives a problem
>> message and finishs the process.
>>
>
> Ok, this sounds like bug #3247 [1] for which the author hasn't applied the
> fix, yet. Rashad, will you have the opportunity to apply just the fix for
> the actual bug (not necessarily the other proposals in the patch), soon, or
> should I do it ?
>

I had pushed fix for compile error ( min and max ). Is it the same error?

>
> Moritz
>



-- 
Regards,
   Rashad
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