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Il 25/07/2022 16:12, Tudorache, Marian ha scritto:<br>
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<div class="WordSection1"><span
style="font-size:11.0pt;mso-fareast-language:EN-US"></span><span
style="font-size:11.0pt;mso-fareast-language:EN-US">When I
open the QGIS project created with QGIS2.18 I got a message
which notify me the project is an old version of QGIS and some
conversion was done.<o:p></o:p></span><span
style="font-size:11.0pt;mso-fareast-language:EN-US"><o:p></o:p></span>
<p class="MsoNormal"><span
style="font-size:11.0pt;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;mso-fareast-language:EN-US">So when
I open QGIS 2.18 project something happened with the data
and was transformed from LineString to MultiLineString.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;mso-fareast-language:EN-US">Is this
normal behaviour for QGIS 3 to convert the geometry type
from single part to multiple parts?<br>
</span><span
style="font-size:11.0pt;mso-fareast-language:EN-US">Is any
method to supress this transformation?</span><br>
<span style="font-size:11.0pt;mso-fareast-language:EN-US"></span></p>
</div>
</blockquote>
<br>
Hi Marian,<br>
AFAIK the QGIS project update process doesn't actually transform any
of your data, it only updates the qgs/qgz file.<br>
<br>
The different behaviour is probably due to a change in the QGIS API
3 and in the way a Shapefile layer is loaded in QGIS 3.<br>
Basic Shapefile layer shape types [1] are:<br>
- Point<br>
- MultiPoint<br>
- PolyLine<br>
- Polygon<br>
<br>
As you can see, there are Point and MultiPoint types, but only
PolyLine and Polygon types and not also MultiPolyLine and
MultiPolygon types.<br>
<br>
In fact, the Shapefile format treats the PolyLine and the Polygon
shape types as layers that can contain both (multi-part) geometries
with only 1 part and (multi-part) geometries with 2 or more parts.
They are actually multi-part layer types.<br>
<br>
With QGIS 2.18, a feature geometry with only 1 part in a PolyLine
shape type Shapefile layer was considered as a LineString WKT
geometry type, while a feature geometry with 2 or more parts in the
same layer was considered as a MultiLineString WKT geometry type.
Thus, you needed to correctly use asPolyline() or asMultiPolyline()
for features geometries in the same PolyLine shape type Shapefile
layer depending on the actual feature geometry type.<br>
<br>
With QGIS 3, both the feature geometry with only 1 part and the
feature geometry with 2 or more parts in a PolyLine shape type
Shapefile layer are considered as MultiLineString WKT geometry type.
Thus, you can always use asMultiPolyline() for all the geometries in
the same PolyLine shape type Shapefile layer.<br>
<br>
Best regards.<br>
<br>
Andrea<br>
<br>
[1]
<a class="moz-txt-link-freetext" href="https://www.esri.com/content/dam/esrisites/sitecore-archive/Files/Pdfs/library/whitepapers/pdfs/shapefile.pdf">https://www.esri.com/content/dam/esrisites/sitecore-archive/Files/Pdfs/library/whitepapers/pdfs/shapefile.pdf</a><br>
<br>
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