[Qgis-user] Segmentation : how to add texture criterion ? (not only colour/spectral variable)

[chris hermansen]

Laurent, list,

On Tue, Mar 4, 2025, 06:06 celati Laurent via QGIS-User <
qgis-user at lists.osgeo.org> wrote:

> Hello.
> My goal is to generate a relevant segmentation that would delimit the main
> physiopnomic units (homogenous areas). Up to now, I have done several tests
> with qgis and orfeotoolbox 9 with the OTB Generic Region merging module : GenericRegionMerging
> — Orfeo ToolBox 7.0.0 documentation
> <https://www.orfeo-toolbox.org/CookBook-7.0/Applications/app_GenericRegionMerging.html>
> with those folowing settings
>
>    - input image : spot 6/7 satelite image (band blue, green, red, near
>    infrared)
>    or Aerial french mapping agency images (50 cms bd ortho with green,
>    red and near infrared).
>    *Homogenity criterion to use : Baatz & Schape
>    - Threshold for the criterion : 500
>    - Number of iterations`: 0
>    - Weight for the spectral homogeneity : 0.1
>    - Weight for the spatial homogeneity : 0.1
>
> The result is rather interesting for certain areas, in particular crops
> areas, without too much vegetation. on the other hand, the method does not
> seems optimal, in particular for forest areas.
> I’m taking the liberty to paste some screenshots :
> the first SS showing interesting result on crop areas :
>
> [image: 4d3f841e567bd5ac5ce37035342c4e71e78d16c6.jpeg]
> A second SS showing the non relevant result on forest areas :
> [image: 9b64943de826eddd230762b3d2a5eb358cc423ec.jpeg]
> Perhaps for these forest areas, the color/spectral criterion is not
> relevant. It would be better to generate / integrate texture information?
> As far as i understood, this GRM OTB module is based only on
> spectral/colour criterion but not take into consideration texture
> information.
> Are there other orfeotoolbox segmentation module that takes into account
> not only the color criterion (spectral) but also texture information?
> If this is not the case, should i create some kind of new raster (add a
> band to my existing color infrared raster) dedicated to texture and/or ndvi
> information?
> Thanks so much for your guidances.
>

Laurent, you don't give us an idea of what forest properties you're hoping
to differentiate.

Forests tend to have a vertical vegetation structure, especially natural
forests; often with dominant species overtop of second and even third tree
species, with other vegetation layers beneath, including shrubs, grasses
and bryophytes going on down to the litter and soil.

In my experience, capturing this kind of complex structure using only
reflectance is difficult. LIDAR can get at least some of this vertical
structure, with some ability to differentiate tree species based on
previously known local height and crown shape characteristics.

But maybe that's more than you're after!

This paper might be of interest to you;

https://www.orfeo-toolbox.org/orfeo-toolbox-and-geobia-classification-of-uav-imagery-in-forest-ecosystems/

Good luck.
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