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

[Moritz Lennert]

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 !

Moritz