Limit a raster processing to a subset/region/mask area?

OTB Usage
1

Dear all,

I’m working in a QGIS environment (graphical interface). Specifically, I’m using a QGIS modeler. Thanks to the processing toolbar provides, i have access to QGIS, Grass, Saga, and Orfeo toolbox tools algo. My goal is to generate a segmentation for geographic area. For the segmentation, I use the OTB tool via QGIS “Generic region merging”: GenericRegionMerging — Orfeo ToolBox 7.0.0 documentation

The complexity comes from the fact that I want to contextualize/differentiate the parameters and input data required for the segmentation step,within my study area based on a land use layer/mask layer. So i want to define specific parameters/input data for the segmentation generated on forest areas. And other input data/segmentation parameters generated for non-forest areas (urban, agricultural). I therefore have a vector data set, “Forest DB mask,” which allows me to locate/mask forest areas.

I therefore want to :

  1. Generate an initial “raster segmentation” from an aerial/satellite image with specific parameters for forest areas (segmentation calculation only for raster pixels that overlap my forest DB mask). Therefore, the calculation must NOT be performed/ be ignored for pixels not covered by this mask layer (agricultural, urban, etc.).
  2. Then generate a second “raster segmentation” for the rest of the study area that was ignored/skiped during the first segmentation (segmentation calculation only for raster pixels that do not overlap my forest DB mask: agricultural, urban, etc.).
  3. Then, once these two raster segmentations are complete, the idea is to merge them into a single raster. Then, generate a polygonization (raster to vector).

This little workflow isn’t really complicated. But I’m wondering if it’s possible to do it in a QGIS modeling/graphical interface environment. I’d be interested in advice/ideas. Do I must to clip input rasters with the forest DB masking layer? With a management/assignment of “no data values” to ignore the segmentation processing on areas not covered by the mask layer?

I’ve attached below a screenshot that allows you to display an input raster image (here a multispectral Spot6/7 satellite image) and the mask layer (vector forest DB mask) to better visualize the context

SS_MS_masque_bd_foret
SS_MS_masque_bd_foret549×779 172 KB

Thanks so much

2

Hello again,
Following to my previous own post I’m taking the liberty to do a first reaction/addition. I tried clipping my multispectral SPOT6 image with my BD FORET mask (clip a raster with a masking extent coverage) by setting the value -999 (16-bit signed output) for the no data values during clipping. This worked. But when I try segmentation with the OTB GRM tool on this image, the process isn’t ignored in the areas for which I had assigned no data values. The tool segmented the entire image. I sharean additional screenshot showing the pixel values in an area of no data values. The values are indeed set on no data values for the multispectral SPOT6 input image. And you can clearly see that it assigned a value to my segmentation result. The process has been done for no data values also :

image
image459×261 40.2 KB

Thanks again