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

[Rashad Kanavath]

On Fri, Feb 3, 2017 at 3:07 PM, Moritz Lennert <mlennert at club.worldonline.be
> wrote:

> On 03/02/17 14:06, Rashad Kanavath wrote:
>
>>
>>
>> On Wed, Jan 25, 2017 at 11:22 AM, Moritz Lennert
>> <mlennert at club.worldonline.be <mailto: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?
>>
>
> No, it was the error explained in #3247. But the issue was fixed and since
> then MarkusM has significantly build upon your work on i.superpixels.slic.
> We now have a nicely functioning module. Thank you for your great work on
> this !
>

Sorry. I saw that later. l SLICO and other options needs to be added I
think.

>
> Moritz
>



-- 
Regards,
   Rashad
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