[GRASS-user] Question to the input seed grid of i.segment
Rashad Kanavath
mohammedrashadkm at gmail.com
Sun Feb 5 03:05:16 PST 2017
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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