Provided by: grass-doc_7.8.2-1build3_all 
NAME
v.category - Attaches, deletes or reports vector categories to map geometry.
KEYWORDS
vector, category, layer
SYNOPSIS
v.category
v.category --help
v.category [-gt] input=name [layer=string[,string,...]] [type=string[,string,...]] [ids=range]
[output=name] option=string [cat=integer] [step=integer] [--overwrite] [--help] [--verbose]
[--quiet] [--ui]
Flags:
-g
Shell script style, currently only for report
Format: layer type count min max
-t
Do not copy attribute table(s)
--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[,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
type=string[,string,...]
Input feature type
Options: point, line, boundary, centroid, area, face, kernel
Default: point,line,centroid,face
ids=range
Feature ids (by default all features are processed)
Example: 1,3,7-9,13
output=name
Name for output vector map
option=string [required]
Action to be done
Options: add, del, chlayer, sum, report, print, layers, transfer
add: add a category to features without category in the given layer
del: delete category (cat=-1 to delete all categories of given layer)
chlayer: change layer number (e.g. layer=3,1 changes layer 3 to layer 1)
sum: add the value specified by cat option to the current category value
report: print report (statistics), in shell style: layer type count min max
print: print category values, layers are separated by ’|’, more cats in the same layer are separated
by ’/’
layers: print only layer numbers
transfer: copy values from one layer to another (e.g. layer=1,2,3 copies values from layer 1 to layer
2 and 3)
cat=integer
Category value
Default: 1
step=integer
Category increment
Default: 1
DESCRIPTION
v.category attaches, copies, deletes or reports categories of vector geometry objects. Further on,
v.category adds a number given by the cat option to categories of the selected layer. These categories
(IDs) are used to assign IDs or to group geometry objects into categories (several different geometry
objects share the same category). These categories are also used to link geometry object(s) to attribute
records (from an attribute table linked to vector map).
NOTES
Use v.to.db to upload related categories to a linked attribute table.
The type parameter specifies the type of geometry objects to which the category is added; it is similar
to an input filter - only the geometry specified in ’type’ is processed.
If the type parameter is set to centroid and the option parameter set to add, new categories will be
added to existing centroids. Note however, that new centroids cannot be created this way. To do so, they
must be added manually using wxGUI vector digitizer or by running v.category with the type parameter set
to area.
If categories are copied with option=transfer, a warning is issued if categories already exit in the
layer they are copied to. In this case the user must make sure beforehand that copying categories from
one layer to another layer does not cause undesired grouping of different geometry objects into the same
categories. This can be avoided by specifying only one layer. The module will then find the next free
layer number and copy categories to there. The new layer number is reported at the end.
Areas are a special case because it is impossible to attach a cat to an area without a centroid; in this
case, the module places new centroids in areas automatically for type=area.
The cat parameter is only used with option=add, option=sum and option=del.
Categories can be deleted for the given layer with option=del. If cat is set to -1, all categories for
the given layer are deleted. If cat is zero or positive, only this category value will be deleted. By
default, cat is set to 1 which means that only categories of value 1 will be deleted.
With option=report, the module reports for each layer and type the total number of categories, the
minimum and the maximum category number. If there are e.g. two lines with line 1 having category 1 and
line 1 having categories 1 and 2, then there are a total of three category values with minimum 1 and
maximum 2.
The ids parameter specifies the list of feature IDs to which the operation is performed; by default, all
vector feature ids are processed. The feature ID is an internal (unique) geometry ID that all vector
primitives possess, and is separate from any category the feature may also possess. Use
v.edit map=inputname tool=select
to find out the geometry ids of certain features.
EXAMPLES
Report vector categories
v.category input=testmap option=report
LAYER/TABLE 1/testmap:
type count min max
point 0 0 0
line 1379 1 1379
boundary 0 0 0
centroid 0 0 0
area 0 0 0
all 1379 1 1379
Delete all vector categories in layer 1
v.category input=testmap output=outmap option=del cat=-1
Add vector categories in layer 1 with step=2
v.category input=outmap output=stepmap option=add step=2
# report
v.category input=stepmap option=report
LAYER/TABLE 1/outmap:
type count min max
point 0 0 0
line 1379 1 2757
boundary 0 0 0
centroid 0 0 0
area 0 0 0
all 1379 1 2757
Add categories/centroids to a vector map without categories
v.category input=wkt output=wktnew option=add
Results can be tested using d.what.vect.
Copy categories from layer 1 to layer 2,3,4,5,6,7 and 8
Existing layer will be overwritten, non-existing will be created.
v.category input=observer output=observer_new option=transfer layer=1,2,3,4,5,6,7,8
Print vector categories of given layer
Print vector categories from the first layer, only for feature ids 1-50.
v.category input=roads option=print layer=1 id=1-50
SEE ALSO
v.centroids, v.db.connect, v.edit, v.to.db
AUTHOR
Radim Blazek, ITC-irst, Trento, Italy
Modified (the id parameter) by Martin Landa, FBK-irst (formerly ITC-irst), Trento, Italy, 2008/02
SOURCE CODE
Available at: v.category source code (history)
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