v.multi2singlepart: a new addon to split multipart to singlepart poly…

…gons (#1021)

Addon to split multipart polygons to singlepart polygons

Co-authored-by: Edouard Choinière <[email protected]>

src/vector/v.multi2singlepart/Makefile

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+MODULE_TOPDIR = ../..
+
+PGM = v.multi2singlepart
+
+include $(MODULE_TOPDIR)/include/Make/Script.make
+
+default: script

src/vector/v.multi2singlepart/v.multi2singlepart.html

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+<h2>DESCRIPTION</h2>
+
+<em>v.multi2singlepart</em> creates a vector layer containing 
+singlepart polygon features generated by separating the multipart 
+features of the input vector layer. The attributes of the input layer 
+will be maintained in the output vector layer. Singlepart features will 
+not be affected.
+
+<p>
+<div align="center" style="margin: 10px"> <a href="example.png"> 
+<img src="example.png" alt="From multipart to singlepart features" 
+border="0" width=400 height="auto"> </a><br> <i>From multipart to singlepart polygons.</i> </div>
+
+
+<h2>NOTES</h2>
+
+To go from singlepart to multipart features, use the 
+<em>v.dissolve</em> function (see example below).
+
+
+<h2>EXAMPLES</h2>
+
+The example uses the layer <i>boundary_municp</i> from the North 
+Carolina dataset. You can download the sample data set from the <a 
+href="https://grass.osgeo.org/download/data/">GRASS GIS website</a>
+
+<div class="code">
+<pre>
+v.dissolve input=boundary_municp column=MB_NAME output=bnd_municp_dis
+v.multi2singlepart input=bnd_municp_dis output=bnd_municp_split
+</pre>
+</div>
+
+<h2>SEE ALSO</h2>
+
+<em> <a 
+href="https://grass.osgeo.org/grass-stable/manuals/v.dissolve.html">v.dissolve</a> 
+</em>
+
+
+
+<h2>AUTHOR</h2>
+
+Paulo van Breugel, paulo at ecodiv.earth

src/vector/v.multi2singlepart/v.multi2singlepart.py

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+#!/usr/bin/env python
+
+#
+############################################################################
+#
+# MODULE:       v.multi2singlepart
+# AUTHOR(S):    Paulo van Breugel
+# PURPOSE:      Split multipart polygon features into singlepart features
+#
+# COPYRIGHT:   (C) 2024 Paulo van Breugel and the GRASS Development Team
+#              http://ecodiv.earth
+#
+#              This program is free software under the GNU General Public
+#              License (>=v2). Read the file COPYING that comes with GRASS
+#              for details.
+#
+#############################################################################
+#
+# REQUIREMENTS:
+# -
+# %module
+# % description: Split multi-part polygons into single-part polygons.
+# % keyword: vector
+# % keyword: geometry
+# %end
+
+# %option G_OPT_V_INPUT
+# % description: Input vector layer
+# % required: yes
+# %end
+
+# %option G_OPT_V_OUTPUT
+# % description: Output vector layer
+# % required: yes
+# %end
+
+# ----------------------------------------------------------------------------
+# Standard
+# ----------------------------------------------------------------------------
+
+# import libraries
+import sys
+import atexit
+import sys
+import uuid
+import grass.script as gs
+
+
+CLEAN_LAY = []
+
+
+def create_temporary_name(prefix):
+    tmpf = f"{prefix}{str(uuid.uuid4().hex)}"
+    CLEAN_LAY.append(tmpf)
+    return tmpf
+
+
+def cleanup():
+    """Remove temporary maps specified in the global list"""
+    maps = reversed(CLEAN_LAY)
+    mapset = gs.gisenv()["MAPSET"]
+    for map_name in maps:
+        for element in ("raster", "vector"):
+            found = gs.find_file(
+                name=map_name,
+                element=element,
+                mapset=mapset,
+            )
+            if found["file"]:
+                gs.run_command(
+                    "g.remove",
+                    flags="f",
+                    type=element,
+                    name=map_name,
+                    quiet=True,
+                )
+
+
+def main(options, flags):
+
+    # Copy layer and remove all but cat column in new layer
+    tmplayer = create_temporary_name("tmp")
+    gs.run_command("g.copy", vector=[options["input"], tmplayer], overwrite=True)
+    cols = gs.read_command("db.columns", table=tmplayer).split("\n")
+    cols = [x for x in cols[1:] if x != ""]
+    gs.run_command("v.db.dropcolumn", map=tmplayer, columns=cols)
+
+    # Check topology
+    top = gs.parse_command("v.info", flags="t", map=tmplayer)
+    if int(top["areas"]) == 0:
+        gs.fatal(_("The layer does not contain areas. Exiting..."))
+
+    # Overlay the original and copied layer
+    gs.run_command(
+        "v.overlay",
+        ainput=options["input"],
+        binput=tmplayer,
+        operator="and",
+        atype="area",
+        btype="area",
+        output=options["output"],
+    )
+
+    # Drop old cat columns
+    gs.run_command("v.db.dropcolumn", map=options["output"], columns=["a_cat", "b_cat"])
+
+    # Change the column names to the original names
+    for colname in cols:
+        oldcol = f"a_{colname}"
+        gs.run_command(
+            "v.db.renamecolumn", map=options["output"], column=[oldcol, colname]
+        )
+
+
+if __name__ == "__main__":
+    atexit.register(cleanup)
+    sys.exit(main(*gs.parser()))