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<p>Good Day:</p>
<p>I would have a look at the masked raster and confirm the no data
value (-999) is written to the header so that it is recognized by
the segmentation routine. Another option would be to delete the
segmented polygons from your result layer (if your result is a
vector) or using the raster calculator to reset these pixels to
-999. <br>
</p>
<p>Kirk Schmidt<br>
</p>
<div class="moz-cite-prefix">On 6/13/2025 8:12 AM, celati Laurent
via QGIS-User wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAHByMH1=0_=ma32nsaXcG73gPmv32vEKhQ+WJwmcDc-G4_WZxw@mail.gmail.com">
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<div dir="ltr">
<div><span class="gmail-HwtZe" lang="en"><span
class="gmail-jCAhz gmail-ChMk0b"><span
class="gmail-ryNqvb">Hello again,</span></span></span></div>
<div><span class="gmail-HwtZe" lang="en"><span
class="gmail-jCAhz gmail-ChMk0b"><span
class="gmail-ryNqvb">Following to my previous own post
I'm taking the liberty to do a first reaction/addition.</span></span>
<span class="gmail-jCAhz gmail-ChMk0b"><span
class="gmail-ryNqvb">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.</span></span><span
class="gmail-jCAhz gmail-ChMk0b"><span
class="gmail-ryNqvb">
This worked.</span></span> <span
class="gmail-jCAhz gmail-ChMk0b"><span
class="gmail-ryNqvb">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.</span></span> <span
class="gmail-jCAhz gmail-ChMk0b"><span
class="gmail-ryNqvb">The tool segmented the entire
image.</span></span> <span
class="gmail-jCAhz gmail-ChMk0b"><span
class="gmail-ryNqvb">I sharean additional screenshot
showing the pixel values in an area of no data values.</span></span>
<span class="gmail-jCAhz"><span class="gmail-ryNqvb">The
values are indeed set on no data values for the
multispectral SPOT6 input image.</span></span> <span
class="gmail-jCAhz"><span class="gmail-ryNqvb">And you can
clearly see that it assigned a value to my segmentation
result. The process has been done for no data values
also : <br>
</span></span></span><img
src="cid:part1.dYd2Y782.fS9wHGS8@nortekresources.com"
alt="SS_raster_segmentation_spot6_nodatavalues.jpg" class=""
width="306" height="171"><br>
</div>
<div>Thanks.</div>
</div>
<br>
<div class="gmail_quote gmail_quote_container">
<div dir="ltr" class="gmail_attr">Le ven. 13 juin 2025 à 11:58,
celati Laurent <<a href="mailto:laurent.celati@gmail.com"
moz-do-not-send="true" class="moz-txt-link-freetext">laurent.celati@gmail.com</a>>
a écrit :<br>
</div>
<blockquote class="gmail_quote"
style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div dir="ltr">
<div>Dear all,</div>
<div>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": <a
href="https://www.orfeo-toolbox.org/CookBook-7.0/Applications/app_GenericRegionMerging.html"
target="_blank" moz-do-not-send="true"
class="moz-txt-link-freetext">https://www.orfeo-toolbox.org/CookBook-7.0/Applications/app_GenericRegionMerging.html</a></div>
<br>
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.<br>
<br>
<div>I therefore want to :</div>
<div>
<ol>
<li>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.).</li>
<li>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.).</li>
<li>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).</li>
</ol>
</div>
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?<br>
<br>
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.<br>
<div><br>
</div>
<div><img
src="cid:part2.3T90hMsn.59W2YcVp@nortekresources.com"
alt="SS_MS_masque_bd_foret.jpg"
style="margin-right: 0px;" class="" width="346"
height="491"><br>
<br>
</div>
<div>Thanks so much.</div>
<div><br>
</div>
<br>
</div>
</blockquote>
</div>
<br>
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</blockquote>
<pre class="moz-signature" cols="72">--
Kirk Schmidt, MScF, BScF, RPF
General Manager
Nortek Resource Solutions Inc.
26 Church Road
Sutherlands River, NS
B0K 1W0
Tel (902) 922.3607
Email: <a class="moz-txt-link-abbreviated" href="mailto:kirk@nortekresources.com">kirk@nortekresources.com</a>
Web: <a class="moz-txt-link-abbreviated" href="http://www.nortekresources.com">www.nortekresources.com</a></pre>
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