Convert diagonally adjacent pixels into one polygon?
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I am trying to vectorize a raster whose digital numbers indicate different classes they belong to. I want to get a single polygon for each class. It would be fine if the shape of the resulting polygons does not exactly follow the contour of the source-pixels. ArcGIS and QGIS yield similar, unwated results: separate shapes out of pixels sharing the class that are adjacent only diagonally. This question has been also posted here in GIS.StackExchange.com, and it is related with this question and this one, also posted in GIS.StackExchange.
I tried the suggestions posted in those questions, but none of them worked for me. I can not use the buffering-approach because my polygons refer to networks of areas; the connectivity/topology of those networks must remain intact, and I have nodes very close to each other. Dissolve is not useful either; it apparently does not work on polygons sharing a single vertex.
ILWIS could solve the issue:
I found that the vectorization tool of ILWIS (see explanation here) has an option for scanning for the 8 neighboring pixels during the targeting of each raster pixel to a polygon. ILWIS calls it "Output map 8-connected with smoothing". This might solve the issue by avoiding the polygon breakage during the vectorization when input pixels are placed diagonally.
I downloaded and installed the ILWIS version available here. However, after importing the raster I want to vectorize (I used the built-in GDAL option), the drop-down menu to select the input layer in the 'Raster to Polygon' tool does not allow me to select anything and thus I can not use the tool.
Does somebody know how to use this ILWIS' tool, or how to solve this problem?