xenial (1) v.overlay.1grass.gz

Provided by: grass-doc_7.0.3-1build1_all bug

NAME

       v.overlay  - Overlays two vector maps.

KEYWORDS

       vector, geometry, spatial query, intersection, union, clip

SYNOPSIS

       v.overlay
       v.overlay --help
       v.overlay  [-t]  ainput=name  [alayer=string]   [atype=string[,string,...]]  binput=name  [blayer=string]
       [btype=string[,string,...]]   operator=string  output=name   [olayer=string[,string,...]]    [snap=float]
       [--overwrite]  [--help]  [--verbose]  [--quiet]  [--ui]

   Flags:
       -t
           Do not create attribute table

       --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:
       ainput=name [required]
           Name of input vector map (A)
           Or data source for direct OGR access

       alayer=string
           Layer number or name (vector map A)
           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

       atype=string[,string,...]
           Feature type (vector map A)
           Input feature type
           Options: line, area, auto
           Default: auto

       binput=name [required]
           Name of input vector map (B)
           Or data source for direct OGR access

       blayer=string
           Layer number or name (vector map B)
           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

       btype=string[,string,...]
           Feature type (vector map B)
           Input feature type
           Options: area
           Default: area

       operator=string [required]
           Operator defines features written to output vector map
           Feature  is  written  to  output  if  the result of operation ’ainput operator binput’ is true. Input
           feature is considered to be true, if category of given layer is defined.
           Options: and, or, not, xor
           and: also known as ’intersection’ in GIS
           or: also known as ’union’ in GIS (only for atype=area)
           not: features from ainput not overlayed by features from binput
           xor: features from either ainput or binput but not those from ainput overlayed by  binput  (only  for
           atype=area)

       output=name [required]
           Name for output vector map

       olayer=string[,string,...]
           Output layer for new category, ainput and binput
           If 0 or not given, the category is not written
           Default: 1,0,0

       snap=float
           Snapping threshold for boundaries
           Disable snapping with snap <= 0
           Default: 1e-8

DESCRIPTION

       v.overlay  allows  the  user to overlay two vector maps. Features in ainput can be lines or areas and are
       cut with areas in binput. Simple clipping can be performed with the and operator.

       If areas in ainput are overlaid with areas in binput, it is sometimes necessary to snap areas  of  binput
       to  those  of  ainput,  otherwise  areas  can go missing or many sliver areas can be created. Snapping is
       enabled by default and can be disabled by setting the snap option to a negative value. Recommended values
       are  between 0.00000001 and 0.0001. Using larger values for snapping can have undesired side-effects, but
       may sometimes be necessary to get a clean output (see example below). In general, it  is  recommended  to
       start  with a small snapping threshold, gradually increasing the threshold until the result is reasonably
       clean. Snapping modifies only boundaries in binput, which are snapped to boundaries in ainput. Boundaries
       in ainput are not modified.

       If  the  first  number of the olayer option is greater than 0, then the resulting output map has a merged
       attribute table in the given layer  number.  The  original  column  names  have  a  prefix  (a_  and  b_)
       corresponding to ainput and binput map.

       If  the  second  number  of  the  olayer option is greater than 0, then the categories of ainput in layer
       alayer are transferred to the output layer with the second number.

       If the third number of the olayer option is greater than 0, then the categories of binput in layer blayer
       are transferred to the output layer with the third number.

NOTES

       Currently  only  areas  in  ainput  are  supported  for the operators or and xor! See also v.select.  The
       operator defines what kind of operation will be done. Features are written to output, if the result of an
       operation ainput operator binput is true.

       If the first number of the olayer option is greater than 0, then attributes of the tables from ainput and
       binput are joined into a new table linked to the output map with a new cat column.

       If the second number of the olayer option is greater than 0, then the attribute table of ainput is copied
       to the output map.

       If  the third number of the olayer option is greater than 0, then the attribute table of binput is copied
       to the output map.

       If atype=auto is given than v.overlay determines feature type for ainput from the first found feature.

EXAMPLES

       Preparation of example data (North Carolina sample dataset):
       # Create an empty box for overlaying to ZIP code vector map
       v.mkgrid map=box grid=1,1 position=coor \
                coordinates=584037.093198,201970.387191 box=50000,50000
       # set region to ZIP codes and box vector maps
       g.region vector=zipcodes_wake,box -p res=100 -a
       # enlarge region a bit for "white border" around map in monitor
       g.region n=n+1000 s=s-1000 w=w-1000 e=e+1000 -p
       d.mon wx0

   AND operator
       d.vect map=zipcodes_wake fill_color=0:128:0
       d.vect map=box fill_color=85:130:176
       v.overlay -t ainput=box binput=zipcodes_wake operator=and output=v_overlay_AND
       d.vect map=v_overlay_AND
       v.overlay with AND operator (selected polygons in grey color)

   OR operator
       d.vect map=zipcodes_wake fill_color=0:128:0
       d.vect map=box fill_color=85:130:176
       v.overlay -t ainput=box binput=zipcodes_wake operator=or output=v_overlay_OR
       d.vect map=v_overlay_OR
       v.overlay with OR operator (selected polygons in grey color)

   XOR operator
       d.vect map=zipcodes_wake fill_color=0:128:0
       d.vect map=box fill_color=85:130:176
       v.overlay -t ainput=box binput=zipcodes_wake operator=xor output=v_overlay_XOR
       d.vect map=v_overlay_XOR
       v.overlay with XOR operator (selected polygons in grey color)

   NOT operator
       d.vect map=zipcodes_wake fill_color=0:128:0
       d.vect map=box fill_color=85:130:176
       v.overlay -t ainput=box binput=zipcodes_wake operator=not output=v_overlay_NOT
       d.vect map=v_overlay_NOT
       v.overlay with NOT operator (selected polygon in grey color)

   Overlay operations: AND, OR, NOT, XOR
       Examples based on North Carolina sample dataset:
       # creation of simple dataset
       v.extract input=zipcodes_wake output=poly1 where="cat = 42"
       v.extract input=urbanarea output=poly2 where="cat = 55"
       v.overlay ainput=poly1 binput=poly2 operator=and output=poly_1_2_and
       v.overlay ainput=poly1 binput=poly2 operator=or  output=poly_1_2_or
       v.overlay ainput=poly1 binput=poly2 operator=not output=poly_1_2_not
       v.overlay ainput=poly1 binput=poly2 operator=xor output=poly_1_2_xor
       v.overlay operations: original input polygons

       v.overlay results of AND, OR, NOT, XOR operations

   Polygons overlaid with polygons
       v.overlay ainput=lake binput=province output=lakeXprovince operator=or
       Polygon union of urban area and Census 2000 areas (North Carolina dataset):
       # input maps
       d.vect urbanarea
       d.vect census_wake2000
       # union
       v.overlay ain=census_wake2000 bin=urbanarea out=urban_census2000 operator=or
       # show result, graphically zooming a subset
       g.region n=230400 s=223800 w=655800 e=662400
       d.erase
       d.vect urban_census2000
       # show merged attribute table
       v.db.select urban_census2000 where="cat=108" -v
       cat|108
       a_cat|98
       a_AREA|231001264
       a_PERIMETE|67804.305
       a_TRACT_|98
       a_TRACT_ID|98
       a_RINGS_OK|1
       a_RINGS_NO|0
       a_ID|98
       a_FIPSSTCO|37183
       a_TRT2000|054108
       a_STFID|37183054108
       a_TRACTID|541.08
       a_TRACT|541.08
       b_cat|55
       b_OBJECTID|55
       b_UA|73261
       b_NAME|Raleigh
       b_UA_TYPE|UA
       v.overlay: Polygon union (right) of urban area (left) and Census  2000  (middle)  areas  (North  Carolina
       dataset)

       As  can  be  seen  by the resulting large number of centroids on boundaries, the urban areas do not match
       exactly the Census 2000 areas. In this case a clean result can be obtained by snapping with  a  threshold
       of 0.1 m.

   Lines overlaid with polygons
       Using the North Carolina sample dataset, we clip the roads map to the area of city of Raleigh, preserving
       road attributes in layer 1:
       g.region vector=zipcodes_wake
       # extract Raleigh city:
       v.extract in=zipcodes_wake out=raleigh \
                   where="ZIPNAME = ’RALEIGH’"
       # clip road network to city polygon:
       v.overlay ainput=roadsmajor atype=line binput=raleigh \
                   out=roadsmajor_raleigh operator=and \
                olayer=0,1,0

       v.overlay: Line to polygon clipping

SEE ALSO

        v.db.connect, v.select, g.copy

AUTHORS

       Radim Blazek, ITC-Irst, Trento, Italy
       Markus Metz

       Last changed: $Date: 2015-08-12 02:04:48 +0200 (Wed, 12 Aug 2015) $

       Main index | Vector index | Topics index | Keywords index | Full index

       © 2003-2016 GRASS Development Team, GRASS GIS 7.0.3 Reference Manual