NAME

       v.fill.holes  - Fill holes in areas by keeping only outer boundaries

KEYWORDS

       vector, geometry, fill, exterior, ring, perimeter

SYNOPSIS

       v.fill.holes
       v.fill.holes --help
       v.fill.holes  input=name   [layer=string]    [cats=range]   [where=sql_query]  output=name
       [--overwrite]  [--help]  [--verbose]  [--quiet]  [--ui]

   Flags:
       --overwrite
           Allow output files to overwrite existing files

       --help
           Print usage summary

       --verbose
           Verbose module output

       --quiet
           Quiet module output

       --ui
           Force launching GUI dialog

   Parameters:
       input=name [required]
           Name of input vector map
           Or data source for direct OGR access

       layer=string
           Layer number or name
           Vector features can have category values in different layers. This  number  determines
           which layer to use. When used with direct OGR access this is the layer name.
           Default: 1

       cats=range
           Category values
           Example: 1,3,7-9,13

       where=sql_query
           WHERE conditions of SQL statement without ’where’ keyword
           Example: income < 1000 and population >= 10000

       output=name [required]
           Name for output vector map

DESCRIPTION

       v.fill.holes  fills  empty  spaces  inside  areas,  specifically  it  preserves areas with
       centroids while areas without centroids, which typically  represent  holes,  are  removed.
       v.fill.holes goes over all areas in a vector map and it preserves only outer boundaries of
       each area while removing inner boundaries which are considered holes.   The  holes  become
       part of the area which contained them.  No boundaries of these holes are preserved.
         Figure:  Holes  inside areas are removed. (a) Original areas with holes and (b) the same
       areas but with holes filled.  In case areas have empty space in between them, i.e.,  there
       are  holes  in  the  overall coverage, but not in the areas themselves, v.fill.holes can’t
       assign this empty space to either of these areas because it does not know which area  this
       empty  space  should  belong to.  If the space needs to be filled, this can be resolved by
       merging the areas around the empty space into one by dissolving their  common  boundaries.
       This  turns  the  empty space into a hole inside one single area which turns the situation
       into a case of one area with a hole.
        Figure: Empty space in between two areas does not belong to either area, so it is  filled
       only  after  the boundaries between areas are dissolved, i.e., areas merged into one.  (a)
       Original areas with space in between, (b) one area with a hole after dissolving the common
       boundary, and (c) hole filled.

   Topology
       Strictly  speaking,  in  the  GRASS  topological model, an area is a closed boundary (or a
       series of connected closed boundaries) which may have a centroid.  If it has  a  centroid,
       it is rendered as a filled area in displays and this is what is usually considered an area
       from the  user  perspective.   These  are  the  areas  where  v.fill.holes  preserves  the
       associated outer boundary (or boundaries).  Other closed boundaries, i.e., those without a
       centroid, are not carried over to the output.  All other features  are  removed  including
       points and lines.

   Attributes
       If  a  specific  layer  is selected, attributes for that layer are preserved for the areas
       based on the category or categories associated with each area.  By default, layer number 1
       is  selected.   In  case  there  are  attribute  tables  associated  with  other layers or
       attributes associated with categories of other features than areas  with  centroids,  this
       attribute data is not carried over to the output just like the corresponding geometries.

EXAMPLE

       The  lakes vector map in the North Carolina sample dataset represents islands inside lakes
       as areas distinguished by attributes.  To demonstrate v.fill.holes, we will first  extract
       only the lakes which will create holes where the islands were located.  Then, we will fill
       the holes created in the lakes to get the whole perimeter of the lakes including  islands.
       Remove the islands by extracting everything else (results in holes):
       v.extract input=lakes where="FTYPE != ’ROCK/ISLAND’" output=lakes_only
       Remove the holes:
       v.fill.holes input=lakes_only output=lakes_filled
         Figure:  The  filled  lake (blue) and borders of the original lakes with islands removed
       (light blue).  Figure shows a smaller area in the north of the data extent.

SEE ALSO

           •   v.dissolve for removing common boundaries based on attributes,

           •   v.clean for removing topological issues,

           •   r.fillnulls for filling empty spaces in raster maps using interpolation,

           •   r.fill.stats for filling empty spaces in raster maps using statistics.

AUTHOR

       Vaclav Petras, NCSU Center for Geospatial Analytics, GeoForAll Lab

SOURCE CODE

       Available at: v.fill.holes source code (history)

       Accessed: Thursday Aug 01 11:31:00 2024

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